high level display screens in j2me for sale

CIOs and IT managers are always struggling to improve the availability of corporate data to those who need it to run the business. In the case of salespeople and mobile executives, that"s a tall order. Ideally, you would use the very gear that these people already carry — such as PDAs or cell phones — to act as messaging systems and data terminals that can fetch customer information or place an order.

Unfortunately, the vast differences among these devices — Pocket PCs running Windows CE, PDAs running Palm OS or Linux, cell phones running the Symbian OS — pose significant problems for developers. Even the cell phones from a single vendor such as Motorola (the company I work for) can vary widely in processor type, memory amount, and LCD screen dimensions. Worse, new handsets sporting new features, such as built-in cameras and Bluetooth networking, are released every six months to nine months.

For IT managers whose chief concern is that applications running on device A today also run on device B tomorrow, the best choice among development platforms is J2ME, a slimmed-down version of Java tailored for use on embedded and mobile devices. Most handset vendors implement their own Java VM, and third-party VMs provide Java support in Palm and Pocket PC devices. For a broad range of devices, past, present, and future, J2ME provides a high degree of security and application portability — but not without drawbacks.

As were all editions of Java technology, J2ME was built to provide controlled access to program resources. The run-time architecture uses a “sandbox” mechanism that contains the executing program in a separate, protected memory space. This prevents code malfunctions from damaging other critical components of the run-time environment. Also, the program doesn’t have unfettered access to any low-level hardware or resources outside of the sandbox. Instead, all device operations are conducted via J2ME API calls.

There are good reasons to isolate a program from many of the phone’s functions. Unlike a desktop PC in which a program crash might clobber a word processing session, a cell phone is essentially a two-way radio. The Federal Communications Commission frowns on the improper use of radio transmitters regardless of the culprit — a cell phone’s owner or a malfunctioning program. And you wouldn’t want a Trojan program “phoning home” and transmitting personal information to a cracker. Because over-the-air provisioning allows users to download new applications, this makes the Java security sandbox more important than ever.

However, this protection scheme has its downside. Stated simply, if an API isn’t defined for a specific hardware feature, a developer can’t use that feature. For example, the Sony Ericsson T610 handset comes with an army of features: Bluetooth networking, infrared and serial connectivity, and a built-in digital camera. However, the current APIs in the T610’s J2ME implementation don’t utilize these features. Instead, you must use C++ and the Symbian OS (which lies under the J2ME abstraction layers) to access them.

Most vendors sidestep this issue by providing special Java APIs designed to access proprietary features. Unfortunately, each vendor devises its own unique set of APIs to use similar services. These incompatible APIs defeat J2ME’s prime directive to provide an abstract platform with a consistent interface that accesses all available features across all devices. Using such vendor-specific APIs also ties the application to a particular mobile device, which reduces an IT manager’s options to deploy the application as far as possible across the enterprise.

J2ME limits support for vendor-specific hardware features to accommodate variations among devices. J2ME tackles hardware variations in two ways. First, J2ME defines an abstraction layer known as a configuration, which describes the minimum hardware required to implement Java on an embedded device. The J2ME configuration that addresses resource-constrained devices such as mobile phones and low-end PDAs is the CLDC (Connected Limited Device Configuration).

Second, J2ME defines a second abstraction layer, termed a profile, that describes the device’s hardware features and defines the APIs that access them. Put another way, profiles extend a configuration to address a device’s specific hardware characteristics.

J2ME currently defines one profile for CLDC devices: the MIDP (Mobile Information Device Profile). In addition to stipulating the basic hardware requirements, the MIDP implements the APIs used to access the hardware.

It’s important to understand that a J2ME device can have only one configuration that describes the core hardware. However, multiple profiles are allowed, including the MIDP and vendor profiles that support device-specific features. A vendor can therefore quickly adapt J2ME for a new device by writing profiles for it.

Besides interfaces, the MIDP describes the characteristics of a J2ME application, known as a midlet. Midlets are taxonomically similar to Java applets, the major difference being that a midlet can download data but not additional code through the connection. The end result is that a midlet has the potential to run unaltered on any J2ME-enabled device. Furthermore, because J2ME profiles define the interface, the appearance and behavior of the midlet on different devices is nearly identical. J2ME thus holds out the promise of becoming a universal front-end for client applications that can run on any mobile device.

The astute reader will have no doubt noticed the words “potential” and “nearly” in that last paragraph. Let’s face it: A few limitations in J2ME can hamper application portability. To begin with, subtle variations in each vendor’s J2ME implementation can cause incompatibilities.

Another issue is that if an API doesn’t exist for a specific device feature, you can’t use that feature at all. J2ME does specify optional standards, such as the MMAPI Mobile Media API, which provides support for audio playback and streamed video. Unfortunately, a developer can’t rely on an optional standard being available on every device.

However, J2ME is constantly evolving to address these concerns. In November 2002, the Java Community Process (JCP) released a significant revision to the MIDP specification. Called MIDP 2.0, it adds mission-critical APIs that support secure network connections (via HTTPS) and implements permissions with digital signatures to support trusted code. The specification also provides improved UI elements that offer enhanced form layout for business applications.

Unlike optional standards, a device that uses MIDP 2.0 must implement all the APIs that it describes, thus ensuring their availability to a program. Handsets that support the MIDP 2.0 specification should appear on the market later this year.

Down the road, the JCP proposes a new JTWI (Java Technology for the Wireless Industry) specification. In JTWI, a number of optional J2ME APIs — such as MMAPI and WMA (Wireless Messaging APIs) — become required services.

Even in its current state, J2ME offers developers the ability to write once and deploy a business application across the wide range of wireless gear currently available. J2ME’s abstraction layers also provide a hedge against vendor lock-in, and they help cope with the rapid changes in today’s wireless devices. Developers may have to craft the midlet’s interface to address the lowest-common-denominator display, but that’s a small price to pay compared with writing a custom client application for each device the corporation owns.

This series targets mobile developers more accustomed to J2ME than BREW or even BREW developers interested in lighter and more efficient code production. Largely inspired by the Java GUI model, the present BREW_J2ME framework deals with what’s known in J2ME as a “high-level interface.” It is far from being an exact J2ME match—reasons will be discussed in the article—but exhibits a similar domain abstraction.

We will begin by quickly discussing the gap between BREW and J2ME and how we can narrow the distance, by providing insight into the design process. A thorough presentation of the framework follows.

Since the beginning, Qualcomm tried to position BREW as language neutral, with C/C++ as the best choice—other options being always available for application development [1]. From a technical standpoint, the theory is perfectly plausible—a new language can be always implemented as a static extension, wrapping native BREW functionality. As an added bonus, being an extension, it can immediately reap all the benefits of BREW Distribution System (BDS). This is on the bright side. But what’s left in the shadows?

Such an implementation will be inherently slower (all the OS calls are mediated by BREW) and bulkier than the same implementation directly on top of the OS. Now, speaking of J2ME: BREW offers much more functionality than standard MIDP (even 2.0)—meaning that probably a non-standard API will be offered to fill the gap.

But, of course, choosing one language over another is mostly a business decision and there is no point in comparing their merits. What’s more attractive is to offer Java developers a more familiar way of writing BREW applications using C++. Obviously, this endeavor implies knowing the limits and differences between J2ME and BREW from the point of view of development.

Some differences stem from the Java vs. C++ architectural debate—for example, memory manipulation, multiple inheritance, type safeness, generics, and so forth. There is another category derived mostly from BREW limitations—prominent examples are lack of support for static variables, level of support for C++, cooperative multitasking, developer not insulated from watchdog activity, and the like. Of course, Java on top of BREW means that somehow Java has to absorb all these differences. A third group of dissimilarities is due to a basic design decision such as event model, components, and so forth. And of course, as mentioned before, J2ME is a platform-independent set of specifications with no counterpart for some BREW functionality.

Our declared goal is to ease the creation of “high-level interface” code and associated logic, making life easier for Java developers. This means that, theoretically at least, we could be able to write code like this:

As we could see in the overview, there are various forces influencing the design. Here are some examples in no particular order: no built-in garbage collector; no static variables = no singletons in the sense of [2]; no root Object but safe type generics, and so forth. Considering all these factors, it becomes clear that code as above cannot be written freely in BREW. Reasons might be:

One of the most important decisions is related to memory management and objects lifetime. If there is no delete, who’s responsible for the destruction of our widgets? There are obvious answers, such as stack-based objects and smart pointers for a scope-defined life span or reference counting (that happens to coincide with BREW solution). One solution, used in previous articles, is to register objects and bind their lifetime to the life of the registrar. This implies an additional layer (the registry) and has the advantage of keeping track of all the resources in one place. There is another subtler advantage. too. A C++ application created directly on top of BREW is not a first-rank C++ object but merely a POD structure. That’s why real C++ manipulation explicitly requires such an insulation layer. We will call our registry DisplayableRegistry.

For convenience, every application inherits from an IMidlet abstract class, responsible for declaring and implementing dummy application-level event callbacks (this subject will be discussed later), as well as providing access to the unique instance of DisplayableRegistry. This solves another issue—Singleton implementation. Please note that the mechanism supplied by IMidlet and dynamic polymorphism is not necessary, per se—static polymorphism can do the trick, too. Making every component aware of the application is somehow equivalent with giving them a context.

And, finally, making the registration process as well as the GUID-based BREW initialization process transparent requires an additional construct—a factory. Our first line of code is now:

The next concern is event handling. Apparently, there are important differences between BREW and Java: a unique ID, event loop mechanism versus an implicit, observer-based one. I say “apparently” because one can move freely from one mechanism to the other. Even more: J2ME, for example, shares one of the weaknesses of BREW—the command listener implementation is a close relative of the BREW event loop—usually a hard-to-maintain, huge “switch.” On top of this, listeners are weak-typed constructs, exposing a Displayable interface that has to be cast by the user. Our framework offers a safer approach with type safe, J2SE style listeners. For example, the ListImpl class defines a listener:

Java has a more elegant getSelected() mechanism instead of unique labels to be passed to IMENUCTL_AddItem. This can be easily implemented by using the ubiquitous DisplayableRegistry, this time generating unique numbers to be used internally as IDs. Please note the use of a policy to faster retrieve the IDs in some particular cases.

A striking difference between BREW and Java is error handling, when RTTI based exception handling is not available or might be considered too expensive to be used in BREW. Emulating a try/catch mechanism using setjmp/longjmp is not directly applicable due to problems in destructing auto objects, but other techniques are available (see [4], [5]). As a convenience, we provided an ErrorHandler as a policy—a way to gracefully provide error tracking information.

Our simple application will deal with two lists, each one having four items—{“1″,”2″,”3″,”4”} and {“A”,”B”,”C”,”D”}. Pressing “1,” for example, takes us to the correspondent “A,” pressing “C” switches to “3,” and so on. This logic is embedded in the event handlers: my14ListUsage and myADListUsage.

This first attempt didn’t cover important subjects such as multi-control screens, handling events other than EVT_COMMAND, and controlling the registered resources. The next installment will discuss all these topics as well as mechanisms to extend the framework.

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users" wishes when a user submits their information through our Contact Us form.

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

If a user"s personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user"s personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user"s account.

Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson"s commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice

To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

This chapter explains the Java 2 platform architecture and its security features as they apply to building Java applications. In particular, it describes the various Java platforms and the core security features that contribute to the end-to-end security of Java-based applications running on various systems—from servers to stand-alone computers, computers to devices, and devices to smart cards.

Sun"s Java philosophy of "Write Once, Run Anywhere" has been an evolving success story since its inception, and it has revolutionized the computing industry by delivering to us the most capable platform for building and running a wide range of applications and services. In general, the Java platform provides a general-purpose object-oriented programming language and a standard runtime environment for developing and delivering secure, cross-platform application solutions that can be accessed and dynamically loaded over the network or run locally.

With the release of the Java 2 Platform, Sun categorized the Java technologies under three key major editions in order to simplify software development and deployment. The Java 2 Standard Edition (J2SE) provides the runtime environment and API technologies for developing and executing basic Java applications, and it also serves as the secure foundation for running Java enterprise applications. The Java 2 Enterprise Edition (J2EE), or the J2EE Platform, is a set of standards and API technologies for developing and deploying multi-tier business applications. To support Java on microdevices and embedded systems, Java 2 Micro Edition (J2ME) provides the runtime environment and API technologies for addressing the needs of consumer electronics and devices. With its widespread adoption, today Java technology is enabled and executed from smart cards to microdevices, handhelds to desktops, workstations to enterprise servers, mainframes to supercomputers, and so on.

To facilitate end-to-end security of the Java platform-based application solutions, the Java runtime environment (JRE) and the Java language provide a solid security foundation from the ground up by imposing strong format and structural constraints on the code and its execution environment. This distinguishes the Java platform from other application programming languages—it has a well-defined security architectural model for programming Java-based solutions and their secure execution.

In this chapter, we will explore the various Java platforms and the intricate details of their security architecture that contribute to the end-to-end security of Java-based application solutions. In particular, we will study Java security and the inherent features of the following technologies:

Security has been an integral part of Java technology from day one. Security is also an evolving design goal of the Java community—building and running secure and robust Java-based network applications. The primary reason for Java"s success today as a secure execution environment is the intrinsic security of its architectural foundation—the Java Virtual Machine (JVM) and the Java language. This foundation achieves the basic Java security goal and its definitive ways for extending security capabilities to ensure features such as confidentiality, integrity, trust, and so forth. A second reason for its success is its ability to deliver an interoperable and platform-neutral security infrastructure that can be integrated with the security of the underlying operating system and services.

The JVM is an abstract computing engine that resides on a host computer. It is the execution environment for the Java programming language and has the primary responsibility for executing the compiled code by interpreting it in a machine-independent and cross-platform fashion. The JVM is often referred to as the Java runtime environment. While executing a Java program running on top of the JVM, the JVM insulates the application from the underlying differences of the operating systems, networks, and system hardware, thus ensuring cross-platform compatibility among all of the implementations of the Java platform.

The Java language allows creation of general-purpose programs called Java classes that represent a Java program or an application. The Java classes compile into a format called Java"s executable bytecodes, which are quite similar to the machine language that can run on top of a JVM. The JVM also allows users to download and execute untrusted programs and applications from remote resources or over a network. To support delivery of Java components over the network, the JVM controls the primary security layer by protecting users and the environment from malicious programs. To enable security, the JVM enforces stringent measures ensuring systems security on the host client machine and its target server environments.

Distributing the executable Java bytecode over a network or running automatically inside a Web browser or a client"s machine leads to different security risks and attacks, such as disclosure of the target environment to the untrusted applications and damage or modification of the client"s private information and data. For example, Java applets downloaded from a network are not allowed to have access to, read from, or write to a local file system. They are also not allowed to create network connections to any host system except the one where they are deployed. On the other hand, stand-alone Java applications that reside and run locally as trusted applications are not subjected to these security features. The key issue is that allowing untrusted applications such as Java applets to be downloaded from a network via a Web browser and letting them access certain resources on the host computer paves the way for security breaches and becomes a potential avenue for the spread of viruses. To prevent known security breaches and threats, the JVM provides a built-in Java security architecture model, configurable security policies, access control mechanisms, and security extensions. Because of the built-in JVM safety features, Java programs can run safely and are more securely protected from known vulnerabilities.

Java is a general-purpose object-oriented programming language similar to C++. It delivers platform-neutral compiled code that can be executed using a JVM and is intended for use in distributed application environments, heterogeneous systems, and diverse network environments. The Java language is also designed to provide for the security and integrity of the application and its underlying systems at all levels—from the Java language constructs to the JVM runtime and from the class library to the complete application.

The language defines all primitives with a specific size and all operations are defined to be in a specific order of execution. Thus, the code executed in different JVMs will not differ from the specified order of execution.

The language provides access-control functionality on variables and methods in the object by defining name space management for type and procedure names. This secures the program by restricting access to its critical objects from untrusted code. For example, access is restricted by qualifying the type members as public, protected, private, package, etc.

The Java language does not allow defining or dereferencing pointers, which means that programmers cannot forge a pointer to the memory or create code defining offset points to memory. All references to methods and instance variables in the class file are done via symbolic names. The elimination of pointers helps to prevent malicious programs like computer viruses and misuse of pointers such as accessing private methods directly by using a pointer starting from the object"s pointer, or running off the end of an array.

The Java language is a strongly typed language. During compile time, the Java compiler does extensive type checking for type mismatches. This mechanism guarantees that the runtime data type variables are compatible and consistent with the compile time information.

The language allows declaring classes or methods as final. Any classes or methods that are declared as final cannot be overridden. This helps to protect the code from malicious attacks such as creating a subclass and substituting it for the original class and override methods.

The Java Garbage Collection mechanism contributes to secure Java programs by providing a transparent storage allocation and recovering unused memory instead of deallocating the memory using manual intervention. This ensures program integrity during execution and prevents programmatic access to accidental and incorrect freeing of memory resulting in a JVM crash.

With these features, Java fulfills the promise of providing a secure programming language that gives the programmer the freedom to write and execute code locally or distribute it over a network.

In the previous two sections, we briefly looked at the basic security features provided by the JVM and the Java language. As part of its security architecture, Java has a built-in policy-driven, domain-based security model. This allows implementing security policies, protecting/controlling access to resources, rule-based class loading, signing code and assigning levels of capability, and maintaining content privacy.

In the first release of the Sun Java Platform, the Java Development Kit 1.0.x (JDK) introduced the notion of a sandbox-based security model. This primarily supports downloading and running Java applets securely and avoids any potential risks to the user"s resources. With the JDK 1.0 sandbox security model, all Java applications (excluding Java applets) executed locally can have full access to the resources available to the JVM. Application code downloaded from remote resources, such as Java applets, will have access only to the restricted resources provided within its sandbox. This sandbox security protects the Java applet user from potential risks because the downloaded applet cannot access or alter the user"s resources beyond the sandbox.

The release of JDK 1.1.x introduced the notion of signed applets, which allowed downloading and executing applets as trusted code after verifying the applet signer"s information. To facilitate signed applets, JDK 1.1.x added support for cryptographic algorithms that provide digital signature capabilities. With this support, a Java applet class could be signed with digital signatures in the Java archive format (JAR file). The JDK runtime will use the trusted public keys to verify the signers of the downloaded applet and then treat it as a trusted local application, granting access to its resources. Figure 3-1 shows the representation of a sandbox in the JDK 1.1 security model.

The release of J2SE [J2SE] introduced a number of significant enhancements to JDK 1.1 and added such features as security extensions providing cryptographic services, digital certificate management, PKI management, and related tools. Some of the major changes in the Java 2 security architecture are as follows:

In the Java 2 security architecture, all code—regardless of whether it is run locally or downloaded remotely—can be subjected to a security policy configured by a JVM user or administrator. All code is configured to use a particular domain (equivalent to a sandbox) and a security policy that dictates whether the code can be run on a particular domain or not. Figure 3-2 illustrates the J2SE security architecture and its basic elements.

): In J2SE, all local Java applications run unrestricted as trusted applications by default, but they can also be configured with access-control policies similar to what is defined in applets and remote applications. This is done by configuring a ProtectionDomain, which allows grouping of classes and instances and then associating them with a set of permissions between the resources. Protection domains are generally categorized as two domains: "system domain" and "application domain." All protected external resources, such as the file systems, networks, and so forth, are accessible only via system domains. The resources that are part of the single execution thread are considered an application domain. So in reality, an application that requires access to an external resource may have an application domain as well as a system domain. While executing code, the Java runtime maintains a mapping from code to protection domain and then to its permissions.

Protection domains are determined by the current security policy defined for a Java runtime environment. The domains are characterized using a set of permissions associated with a code source and location. The java.security.ProtectionDomain class encapsulates the characteristics of a protected domain, which encloses a set of classes and its granted set of permissions when being executed on behalf of a user.

): In essence, permissions determine whether access to a resource of the JVM is granted or denied. To be more precise, they give specified resources or classes running in that instance of the JVM the ability to permit or deny certain runtime operations. An applet or an application using a security manager can obtain access to a system resource only if it has permission. The Java Security API defines a hierarchy for Permission classes that can be used to configure a security policy. At the root, java.security.Permission is the abstract class, which represents access to a target resource; it can also include a set of operations to construct access on a particular resource. The Permission class contains several subclasses that represent access to different types of resources. The subclasses belong to their own packages that represent the APIs for the particular resource. Some of the commonly used Permission classes are as follows:

Example 3-1 shows how to protect access to an object using permissions. The code shows the caller application with the required permission to access an object.

Permissions can also be defined using security policy configuration files (java.policy). For example, to grant access to read a file in "c:\temp\" (on Windows), the FilePermission can be defined in a security policy file (see Example 3-2).

Policy: The Java 2 security policy defines the protection domains for all running Java code with access privileges and a set of permissions such as read and write access or making a connection to a host. The policy for a Java application is represented by a Policy object, which provides a way to declare permissions for granting access to its required resources. In general, all JVMs have security mechanisms built in that allow you to define permissions through a Java security policy file. A JVM makes use of a policy-driven access-control mechanism by dynamically mapping a static set of permissions defined in one or more policy configuration files. These entries are often referred to as grant entries. A user or an administrator externally configures the policy file for a J2SE runtime environment using an ASCII text file or a serialized binary file representing a Policy class. In a J2SE environment, the default system-wide security policy file java.policy is located at /lib/security/ directory. The policy file location is defined in the security properties file with a java.security setting, which is located at /lib/security/java.security.

Example 3-3 is a policy configuration file that specifies the permission for a signed JAR file loaded from "http://coresecuritypatterns.com/*" and signed by "javaguy," and then grants read/write access to all files in /export/home/test.

The J2SE environment also provides a GUI-based tool called "policytool" for editing a security policy file, which is located at "/bin/policytool."

The effective policy of the JVM runtime environment will be the union of all permissions in all policy files. To specify an additional policy file, you can set the java.security.policy system property at the command line:

): Each Java application can have its own security manager that acts as its primary security guard against malicious attacks. The security manager enforces the required security policy of an application by performing runtime checks and authorizing access, thereby protecting resources from malicious operations. Under the hood, it uses the Java security policy file to decide which set of permissions are granted to the classes. However, when untrusted classes and third-party applications use the JVM, the Java security manager applies the security policy associated with the JVM to identify malicious operations. In many cases, where the threat model does not include malicious code being run in the JVM, the Java security manager is unnecessary. In cases where the SecurityManager detects a security policy violation, the JVM will throw an AccessControlException or a SecurityException.

In a Java application, the security manager is set by the setSecurityManager method in class System. And the current security manager is obtained via the getSecurityManager method (see Example 3-4).

The class java.lang.SecurityManager consists of a number of checkXXXX methods like checkRead (String file) to determine access privileges to a file. The check methods call the SecurityManager.checkPermission method to find whether the calling application has permissions to perform the requested operation, based on the security policy file. If not, it throws a SecurityException.

If you wish to have your applications use a SecurityManager and security policy, start up the JVM with the -Djava.security.manager option and you can also specify a security policy file using the policies in the -Djava.security.policy option as JVM arguments. If you enable the Java Security Manager in your application but do not specify a security policy file, then the Java Security Manager uses the default security policies defined in the java.policy file in the $JAVA_HOME/jre/lib/security directory. Example 3-5 programmatically enables the security manager.

): The access controller mechanism performs a dynamic inspection and decides whether the access to a particular resource can be allowed or denied. From a programmer"s standpoint, the Java access controller encapsulates the location, code source, and permissions to perform the particular operation. In a typical process, when a program executes an operation, it calls through the security manager, which delegates the request to the access controller, and then finally it gets access or denial to the resources. In the java.security.AccessController class, the checkPermission method is used to determine whether the access to the required resource is granted or denied. If a requested access is granted, the checkPermission method returns true; otherwise, the method throws an AccessControlException.

Codebase: A URL location of class or JAR files are specified using codebase. The URL may refer to a location of a directory in the local file system or on the Internet. Example 3-7 retrieves all the permissions granted to a particular class that"s been loaded from a code base. The permissions are effective only if the security manager is installed. The loaded class uses those permissions by executing Class.getProtectionDomain() and Policy.getPermissions().

To ignore the default policies in the java.security file, and only use the specified policy, use "==" instead of "=". With the policy just presented, you may run the following:

Bytecode verifier: The Java bytecode verifier is an integral part of the JVM that plays the important role of verifying the code prior to execution. It ensures that the code was produced consistent with specifications by a trustworthy compiler, confirms the format of the class file, and proves that the series of Java byte codes are legal. With bytecode verification, the code is proved to be internally consistent following many of the rules and constraints defined by the Java language compiler. The bytecode verifier may also detect inconsistencies related to certain cases of array bound-checking and object-casting through runtime enforcement.

ClassLoader: The ClassLoader plays a distinct role in Java security, because it is primarily responsible for loading the Java classes into the JVM and then converting the raw data of a class into an internal data structure representing the class. From a security standpoint, class loaders can be used to establish security policies before executing untrusted code, to verify digital signatures, and so on. To enforce security, the class loader coordinates with the security manager and access controller of the JVM to determine the security policies of a Java application. The class loader further enforces security by defining the namespace separation between classes that are loaded from different locations, including networks. This ensures that classes loaded from multiple hosts will not communicate within the same JVM space, thus making it impossible for untrusted code to get information from trusted code. The class loader finds out the Java application"s access privileges using the security manager, which applies the required security policy based on the requesting context of the caller application.

With the Java 2 platform, all Java applications have the capability of loading bootstrap classes, system classes, and application classes initially using an internal class loader (also referred to as primordial class loader). The primordial class loader uses a special class loader SecureClassLoader to protect the JVM from loading malicious classes. This java.security.SecureClassLoader class has a protected constructor that associates a loaded class to a protection domain. The SecureClassLoader also makes use of permissions set for the codebase. For instance, URLClassLoader is a subclass of the SecureClassLoader. URLClassLoader allows loading a class or location specified with a URL.

Keystore and Keytool: The Java 2 platform provides a password-protected database facility for storing trusted certificate entries and key entries. The keytool allows the users to create, manage, and administer their own public/private key pairs and associated certificates that are intended for use in authentication services and in representing digital signatures.

We will take a look in greater detail at the usage of the Java keystore and keytool and how these tools help Java security in the section entitled "Java Security Management Tools," later in this chapter.

A book that does not look new and has been read but is in excellent condition. No obvious damage to the cover, with the dust jacket (if applicable) included for hard covers. No missing or damaged pages, no creases or tears, and no underlining/highlighting of text or writing in the margins. May be very minimal identifying marks on the inside cover. Very minimal wear and tear. See the seller’s listing for full details and description of any imperfections.See all condition definitionsopens in a new window or tab

A book that does not look new and has been read but is in excellent condition. No obvious damage to the cover, with the dust jacket (if applicable) included for hard covers. No missing or damaged pages, no creases or tears, and no underlining/highlighting of text or writing in the margins. May be very minimal identifying marks on the inside cover. Very minimal wear and tear. See the seller’s listing for full details and description of any imperfections.See all condition definitionsopens in a new window or tab

Designing applications for small computing devices is a challenge, to say the least,primarily because of the limited resources found in these devices. The small computing device contains minimal memory and storage room for persistent data. Many traditional systems design methods and best practices are simply not appropriate for building applications to run on small computing devices

Asmall computing device has a radically different hardware configuration than traditional computing devices such as desktop computers and servers. Traditional computing devices are under Continuous power from the power grid, while some small computing devices such as cellular telephones rely on battery power that diminishes during the course of operation. Apower grid powers other small computing devices such as set-top boxes and appliances. Another important difference between traditional computing devices and small computing devices is the network connection

1.programs and data are stored in a small computer device’s memory, commonly referred to as primary storage. These are lost when the device drops power, although many devices have a secondary battery to retain programs and data as long as possible. 2.Once lost, programs and data must be reloaded into the device. Secondary storage is not usually available on a small computing device. 3.Therefore, a J2ME application should rely on data stored offline in a desktop computer or server rather than data stored in the device’s primary storage. 4.Data stored offline can be reloaded into the device using a network connection.

5.Don’t expect a mobile small computing device to transmit and receive data at the same rate as a device on a hard-wired network. 6.Data transmission between a mobile small computing device and a traditional computing device is slow in comparison to a hard-wired network connection because radio and infrared technology offers a narrower transmission bandwidth than that found in hard-wired network connections. 7.A bandwidth is the number of communications channels available to transmit bits of data simultaneously.

Many users of your J2ME application expect the same response from your application as they experience from desktop computer applications. Therefore, you must design your J2ME application to minimize and optimize data transmission with offline data sources. One way to optimize your J2ME application is called ROMizing the application for run-time operations. ROMizing creates a machine code image of an application before the application is deployed on the small computing device

Best Practices Over time and through trial and error, J2ME developers have come up with the best way to solve complex J2ME programming problems. And these techniques are called BEST PRACTICES AND PATTERNS. Best practices are proven design and programming techniques used to build J2ME systems. Patterns are routines that solve common programming problems that occur in such systems. Professional developers use best practices and patterns to avoid making common mistakes when designing and building a J2ME application

Typically, you design an application by dividing it into objects that have associated DATA AND METHODS. Let’s use an order form as an example. An order form is an object that has an order number, customer number, product number,and related data. Likewise, an order form has functionality associated with it, such as inserting a new order, modifying an existing order, and deleting an order. And the order form has one or more menu options that enable a user to navigate the order form.

The size of your J2ME application is critical to deploying the application efficiently. The best practice is to remove unnecessary components of your application in order to reduce the size of the overall application.

Limit the Use of Memory In addition to removing unnecessary features from your application, design your application to manage memory efficiently. There are two types of memory management that should be used in the J2ME application. These are overall memory management and peak time memory management. Overall memory management is designed to reduce the total memory requirements of an application. Peak memory management focuses on minimizing the amount of memory the application uses at times of increased memory usage on the device.

A primary way to reduce total memory requirements of your application is to avoid using object types. Instead, use scalar types, which use less memory than object types. Likewise, always use the minimum data type suited for storing data. Peak time memory management requires you to manage garbage collection. J2ME does have a garbage collector, but as with J2SE, you don’t know when the garbage collector will collect your garbage. Therefore, it is critical that you clean up after the application is finished using memory.

This reduces both memory allocation and the need for processing power. Memory allocation is reduced because multiple references can use the same object at different times in the application’s life cycle. Obviously, both objects that use the same memory cannot run simultaneously. The need for processing power is reduced because a portion of the processing required to allocate new memory doesn’t need to be invoked since memory has already been allocated when the object is instantiated.

Small computing devices are designed to run applications that do not require intensive processing because processing power common to desktop computers is not available onthese devices. This means that you must design your J2ME application to perform minimal processing on the small computing device. The alternative is to build a client-service J2ME application or web services J2ME application. There are two levels of operation in a client-service application. These are the client level and the server level. The small computing device runs the client level that provides user interface and presentation functionality to the application. The server-side level processes client requests and returns the result to the small computing device for presentation to the user. Nearly all processing occurs on the server side of the application.

2.The first layer is the client tier, sometimes referred to as the presentation tier. This is where a person interacts with an application. 3.The second layer contains the business logic that is used to fulfill requests from a client by calling appropriate software on the processing tier. 4.Processing software returns results to the business logic layer, and in turn, those results are returned to the client for presentation to the user.

Besides lightening the processing load on the small computing device, you must also be concerned about the availability of a network connection. Cellular telephone networks use technology that attempts to maintain connection as the mobile device moves from one cell to another cell. In reality there are dead zones where the mobile device is outside the range of the cellular telephone transceiver. The drop in communication can occur without warning, as many cellular telephone users have experienced.

Although you cannot avoid a break in communication, you can take steps to reduce the impact on the user of your application. Begin by keeping transmissions short—transfer the minimum information necessary to accomplish a task. Consider using store-forwarding technology and a server-side agent whenever your J2ME application requests a lot of information. A server-side agent is software running on the server that receives a request from a mobile device and then retrieves requested information from a data source, which is very similar to the business logic layer of web services technology.

Most desktop applications have a standard set of graphical user interface objects such as text boxes, combo boxes, radio buttons, check boxes, and push buttons. However, small computing devices use a variety of user display and input devices. Some devices, such as a cellular telephone, have an inch-square display and a telephone keypad for data input. There is a standard display and input for desktop computers, but you cannot say the same about small computing devices. The variety of shapes and hardware configurations found in devices classified as small computing devices makes it nearly impossible to standardize on a set of user interface objects for these devices.

It is critical that you design a user interface that takes advantage of convenient features found on a small computing device and avoid user interactions that are awkward to perform. If you decide to create a user interface containing a menu, consider the available input mechanisms of the small computer device before beginning your design. Some devices have touch screens that enable you to use icons, rather than words, to represent menu options. Other devices, such as cellular telephones, have limited keypads. Let’s say three options are presented in a list on the screen. Typically, you identify each option with a shortcut key that is a sequence of letters (A, B, C), or numbers (1, 2, 3), or a letter within the name of the option.

Use Local Variables Limited resource is the theme that echoes through design considerations for applications that run on small computing devices. As a developer, you cannot assume there are sufficient resources on every small computing device to run your application. You’ll find this line of thought radically different from the mind- set used to write applications for desktop devices and server devices, where you can safely assume that sufficient resources exist to run an application. Data storage is a key area within an application for reducing excessive processing. In many applications, developers assign values to data members of a class rather than using a local variable. You can increase processing of your application if you eliminate the extra steps of accessing a data member of a class by assigning values to local variables.

Concatenating strings is another processing drain that can be avoided by designing an application to eliminate concatenations or at least reduce the number of concatenations to the minimum necessary to achieve the objective of the application.

A string is an array of characters terminated by a NULL and stored sequentially in memory. Let’s assume the application wants to compare two strings, both of which are four characters and reside in memory. The application instructs the small computing device to copy the first character of each string into the CPU for comparison. This process continues until either the null character is reached or a letter pair is different. The entire process might require ten reading instructions and five comparison instructions, depending on when a mismatch is discovered

It is very common for developers to invoke one or multiple threads within an operation. Invoking a thread is a way of sharing a routine among other operations. For example, a sort routine can be shared simultaneously by multiple operations that must sort data. Each operation invokes the sort routine independent of other operations, although the same code is being executed for all operations.

Deadlocks and other conflicts might arise when multiple operations use the same routine. These problems are avoided by synchronizing the invocations of a thread, as you probably remember when you learned Java programming. Always use a thread whenever an operation takes longer than a tenth of a second to run because a thread requires less overhead than non-thread invocation methods, and therefore you’ll see a performance increase in your application.

A common way of reducing the overhead of starting a new thread is to create a group of thread objects that are assigned threads as needed by operations within an application. Less processing is required to assign a thread to an existing thread object than to create a new thread object. Grouping thread objects is made possible by the ThreadGroup class, but J2ME does not support this class. You can work around it, however, by creating your own grouping using the Collection class. You can store groups of thread objects in a collection and then use standard collection methods to start and stop threads in the collection and assign threads to particular thread objects within the collection.

Version management is always a concern of application developers, especially when applications are invoked from within a small computing device. You can reduce and possibly eliminate problems associated with multiple versions of the same application by requiring invocation of the application from a web server. Here’s how a small computing device can invoke a web server–based J2ME application: midp -transient Rather than running a local JAD file, the -transient option specifies that the JAD file is located on a web server identified by the URL on the command line. In this way, the developer only needs to update one copy of the application, and distribution is handled by making the latest version of the application available on the web server.

There will likely be occasions when you need to have your application perform in a certain way, depending on the type of small computing device that runs the application. First, design your application with switches that activate and/or deactivate routines depending on the value of a setting. A setting is a value assigned to a variable that is either created within the application or passed to the application as a command line parameter. J2ME applications are capable of reading the value of a setting from a JAD file and manifest file.

The J2ME program in Listing 4-2 illustrates how to read this user-defined value during run time without having to recompile or repackage the application. A user-defined value is read by invoking the getAppProperty() method and passing the name of the user-defined value to the getAppProperty() method. The getAppProperty() returns the user-defined value from either the manifest file or the JAD file depending on which of these files contains the user-defined value. Model-Version user-defined value defined in the JAD file and displays the value on the screen. Of course, you can create a compound statement that invokes the getAppProperty() method and then assigns the returned value to a variable or uses the return value directly in an expression.

MIDlet-Version: 2.0 MIDlet-Vendor: MyCompany MIDlet-Jar-URL: MIDlet-1: BestMIDlet, /images/BestMIDlet.png, Best.BestMIDlet Model-Version: M253 public class BasicMIDletShell extends MIDlet { public void startApp() System.out.println(getAppProperty("Model-Version")); } public void pauseApp() public void destroyApp( boolean unconditional)

A drop-down box is a convenient way for users to choose an item from a list of possible items, such as an abbreviation for a state. Traditionally, content of a drop-down box is loaded from the data source once when the application is invoked and remains in memory until the application terminates. While caching the contents in memory is a best practice in Java programming, caching is a questionable practice when developing a J2ME application. Loading a list of data for a drop-down box when the J2ME application is invoked is efficient if this is a short list that doesn’t require substantial memory resources. Load the list dynamically from a server whenever the list is long. Release the list once the user has made a selection, and then reload the list the next time the drop-down box is invoked. In this way, memory used to store the list can be reused between calls to the drop-down box.

Nearly every J2ME application has an interface that enables user interactions with the application. The user interface can be as simple as pressing a button on the small computing device, which causes the application to react, or as complex as displaying a form containing check boxes, radio buttons, lists, and other objects common to many applications. Selections made by a user are considered events that are forwarded to your application by the device’s application manager for processing. The application’s developer must write code that recognizes an event and then reacts to the event by performing a task based on the nature of the application.

J2ME User Interfaces A user interface is a set of routines that displays information on the screen, prompts the user to perform a task, and then processes the task. For example, a J2ME application might display a list of menu options, such as Inbox, Compose, and Exit, and then prompt the user to make a selection by moving the cursor keys and pressing a key on the small computing device. The device’s application manager passes the selection to the application, where it is compared with known options. If a match occurs, the application performs the steps necessary to process the option. A developer can use one of three kinds of user interfaces for an application. These are a command, form, or canvas.

A command-based user interface consists of instances of th