With the rapid development of the Internet network, Internet-based enterprise applications require software platforms with openness, distribution and platform-independence. Then there is a technique such as RPC / COM / CORBA, but there are many shortcomings and limitations in practical applications. Their specific protocols are difficult to pass through the firewall, so it is not suitable for application development on the Web. In order to further develop web-based applications, Sun ONE (Open Net Environment Development Network Environment) and Web Services Technologies of Microsoft's .NETs. Sun One architecture is based on Java language, including J2SE / J2EE / J2ME and a series of standards, technologies and protocols. It includes Sun's unique IPlanet software series, including Welcome LDAP directory server software on the market, and Forte for Java, which is easy to write software tools for Java languages in any environment. We can easily get free from the Internet and using products such as Java integrated development environment, Java database, and middleware (Application Server) servers, and their source code. Sun One is closer to or can meet the Internet requirements of distribution, development and platform in intelligent web services. With the continuous development of Java technology, it is further subdivided according to the market: J2EE (Java 2 Enterprise Edition) for enterprise network, J2SE (Java 2 Standard Edition) for common PC applications and an embedded device and consumer electrical appliance Three versions of J2ME (Java 2 Micro Edition). This article makes some introductions on Sun One Java core applications - J2SE / J2EE / J2ME. J2EE Technology Application J2EE is a new concept of Sun Company, which is more advantageous than traditional Internet application models. J2EE Model J2EE's Application Programming Model (J2EE BluePrints) provides an architecture model for implementing a document and instance suite based on J2EE multi-layer applications, simplifying this complex work. It is used by developers as designing and optimizing components so that developers are divided into development work from strategies. J2EE Application Programming Model requires developers to divide their work into two categories: commercial logic and representation logic, and the rest is automatically handled by system resources without having to encode intermediate tubes. This way, developers can spend more time in business logic and representation logic. This transformation is popular with companies that pay attention to shortening project cycles. The J2EE platform J2EE platform is a standard environment that runs J2EE applications, which is composed of J2EE deployment specification (a standard that all J2EE platform products must be supported), IETF standard sets, and CORBA standards. The latest J2EE platform also adds a JavaBean component model. Developers can use the JavaBean component model from defining Java class instances and access Java classes through the defined events. J2EE supports EJB, so developers can perform multi-user transaction functions. Enterprise JavaBeans divide the application logic into reuse and scalable code segments when running on the J2EE server. Enterprise Javabeans is not new features, but by defining standard clients and service APIs, J2EE enhances its ability and portability. EJB runs within one container of the server, providing all typical interlayers, such as transaction management, security, remote customer connection, survival cycle management, and database connection buffers. In order to allow the transaction system to operate in the presence of an EJB container, developers only need to define the transaction attribute of Beans in the deployment description file.
J2EE is a standard design model for developing multi-level, slim customer user programs; 2. J2EE Platform, is a standard design model for developing multi-level, thin client user programs; 2. J2EE Platform is a standard The platform used to integrate the J2EE application and specify a series of interfaces and methods; 3. J2EE Compatibility Test Suite is a set of compatible test components to detect whether the product is compatible with the J2EE platform; 4.J2ee Reference Implementation, The ability to demonstrate J2EE. J2EE Server Sun's J2EE Server provides naming and directory services through Java Naming and Directory Interface (JNDI), authentication, HTTP, and Enterprise JavaBeans compatible. JNDI is a standard extension of the Java platform, providing Java features to the company's naming and directory services, with a unified interface, including LDAP. The J2EE server also uses Java servlet technology. Java servlets can be seen as a small program running on the server, providing developers to create web applications based on components-based, independent ways. It is unlikely to have performance limitations as using CGI. Java Servlet is a simple skill for extending web server features. Since it is written in Java, it is possible to access the entire Java API library, including JDBC APIs for accessing the enterprise database. JSP is an extension of Java Servlet. Java servlet provides development and display of interactive web pages from the server. Today, JSP has further improved, which makes it easier to create and support the HTML and XML pages combined with static templates and dynamic content. The security J2EE platform defines a standard public access control rule that has been defined and explained by the apprier when the program is developed on the corporate platform. J2EE also needs to provide a standard registration mechanism so that the application does not mix these registration mechanisms and logic, so that the same operation is performed in a large number of different environments and does not need to change the source code. For example: J2EE application developers can specify several security levels, when users access data, they can write up code to check the level of current user privileges. In the development phase, developers give multiple sets of user appropriate security levels, enabling applications to easily determine the limit level before performing restrictions. The J2EE platform is the best platform for Java technology enterprise applications, which allow programmers to develop and distribute enterprise-class applications quickly, quickly and quickly. The following is its related technique: 1.enterprise JavaBeans Architecture, enterprise JavaBeans defines an application interface. It allows programmers to develop, publish and manage cross-platform, component-based enterprise applications. 2. JavaServer Pages, JSP technology provides a simple and quick way to create dynamic web pages. Through it, it can quickly develop web-based applications, and these applications are independent of the platform. Because JSP is very similar to the ASP, it is easy to familiarize with ASP. 3.java servlet provides an application interface. It can be developed and extended quickly and quickly. In terms of development trends, it may replace CGI in the future. 4.J2ee Connector provides a standard structure to connect different enterprise information platforms. 5. Java Naming and Directory Interface (JNDI), between Java platforms and commercial information, JNDI provides a unified, seamless standardized connection. By using JNDI, programmers can transfer Java applications between enterprises with more names and directory services.
6. Java Interface Definition Language (JIDL), by using CORBA, the ability to work together can be provided. JIDL includes an IDL-To-Java compiler and an ORB supporting IIOP (Internet Inter-ORB Protocol). 7.JDBC, almost all of the database provides a unified interface, and you can create advanced tools and interfaces. 8. Java Message Service (JMS), which depends on all enterprise-class messaging services, such as reliable queries, publishing messages, subscribes to magazines, and other applications, and provides a standard interface for them. 9.Java Transaction API (JTA), which specifies a senior management specification for the application of applications in distributed systems. 10.javamail, JavaMail application interface provides an abstract class of a complete set of email systems. With JavaMail, you can create a message or message application. 11.RMI-IIOP, use it to develop remote interfaces with the server with the server with Java technology and Java RMI interface. J2EE bundles a module using a fixed file format: bundle the J2EE application with .ser file; bundle Enterprise Bean with .jar. For example, one .ear file contains a .xml file as its distribution description, also contains one or more .jar and .war files; one .jar file except for its distribution description, it also contains .class as Enterprise Bean. file. The development phase of the J2EE application is divided into four steps: 1.Enterprise bean creation; 2.Web Component creation; 3.j2ee application assembly; 4.j2ee application distribution. The following is a J2EE compatible products partial list: BEA WebLogic Server 6.0, Borland App Server, HP Bluestone Total-e-Server, IBM WebSphere Application Server, IONA iPortal Application Server, iPlanet Application Server, Macromedia JRun Server, Oracle 9i Application Server, SilverStrean Application Server, Sybase Easerver, TOGETHERSOFT ControlCenter, Java 2 SDK Enterprise Edition. J2ME technology J2ME (Java 2 Platform Micro Edition) is designed for the wireless electronic market, including JVM specifications and API specifications. Its API specification is based on J2SE (Java 2 Standard Editon). J2ME defines a set of suitable class libraries and virtual machine technology. These technologies can make users, service providers, and equipment manufacturers through physical (wired) connection or wireless connection, and use rich applications at any time. J2ME is also known as Java 2 micro version, is used on a wide variety of consumer electronics, such as smart cards, mobile phones, PDAs, TV set-top boxes. Of course, J2ME also provides a Java language consistent characteristic, which is transfers cross-platform and secure network transmission. It uses a series of smaller packages, and javax.microedition.IO is a subset of J2SE packages. J2ME can be upgraded to J2SE and J2EE. Before the J2ME appears, we have more contact with Java Card, embedded Java (Embedded Java), and real-time Java (Real Time Java).
Among them, the Java card is a minimum Java subset of SIM cards, smart cards, etc., which is small than J2ME, and is not portable. Embedded Java configures Java class libraries and VM (Virtual Machine, virtual machines) for special users. It is very small for resource demand, and can be operated on devices that have a graphical user interface and network, but it can not be transplanted. Real-time Java is implemented by the real-time custom Java expert group led by IBM, and is still in constant improvement. However, in strict sense, they are not true J2mes. Like other versions, J2ME has many Java technical features, mainly: 1. You can run on various devices that support Java; 2. Small code; 3. Take advantage of Java language; 4. Good security; 5. Apply for J2ME can be easily upgraded to J2SE, J2EE. J2ME configuration and framework in order to support the flexibility and availability requirements proposed by users and embedded markets, J2ME is designed to be more modular and removable. J2ME builds 3-layer software on the original operating system to achieve this requirement: 1.JVM layer, this layer is based on the host operating system, according to a certain J2ME configuration, implements JVM. 2. Configure the layer, this layer is low for the user visibility, but is very important to the framework layer. It defines the minimum set of functions of Java virtual machines and the minimum collection of Java class libraries in the "Level" market. In a sense, the configuration layer defines the "minimum blend mother" of the developer to use Java features and libraries on all devices. 3. Frame layer, this layer is the most common for users and application providers. It defines the smallest set of Java virtual machines and the minimum collection of Java class libraries in the "vertical" market. The framework is achieved based on a specific configuration layer. As long as the device supports the same framework, the application developed for a particular frame layer can be ported to other devices. A device can support multiple frame layers. In J2ME devices, JVM is closely linked to the configuration layer, which reflects the basic functions of each type of device. The frame layer specifies additional APIs on the configuration layer for different devices. In order to meet the continuous updated application, the framework can expand the new Java library class. In the near future, as the new device continues to appear, J2ME technology will provide a wide range of frame layers, configuration layers, and VMs. JAVA Community Process provides specifications for customers and developers. According to JCP definition, J2ME is currently a "Connected Device Configuration", which uses typical Java virtual machine technology. This full-featured VM contains all functions of a virtual machine on a desktop system that apply to devices with at least a few megabyte memory. For wireless devices and other devices that have insufficient memory, J2ME uses "Configuration Configuration" (CLDC) technology for connection. KVM is the core feature of J2ME. It is a very portable JVM, dedicated to small memory, limited resources, equipment that can be internetrated, such as cellular phones, pagers, and personal organizers. These devices typically contain 16 or 32-bit processors, minimum 128KB memory. KVM can be flexibly applied to various industries, on various types of devices, and can adapt to problems caused by the diversification of these devices, such as the power consumption of the processor, the size of the memory, the specific function of the device, and application. And other issues. The CLDC technology CLDC defines the target Java platform, which is based on small, less resources, and only 160 to 512K devices. CLDC is composed of KVM and is composed of core library classes and interfaces such as cellular phones, digital products, two-way pager, personal organisms and household appliances.
There are many advantages to using CLDC technology: 1. Cross-platform, this has retained Java consistent features, and the application does not change as platform differences. 2. Dynamics, this is also very attractive, you can download your favorite application and service as needed, and can communicate with other CLDC devices. 3. Security, the characteristics of Java itself have created this feature. Compared to J2SE, CLDC lacks the following characteristics: 1.AWT (Abstract Window Development Kit), Swing or other graphics library; 2. User defined type loader; 3. Finalization of class instance; 4. Weak reference ; 5.RMI; 6.Reflection. CLDC has four packages: java.lang, java.util, java.io and javax.microedition. In addition to the javax.microedition package, several other packages are the core subset of J2SE packages. CLDC uses these J2SE libraries, but some of them are not used in miniature devices, attributes and methods. J2ME Defines two configurations: Connected Device Configuration (Connection Device Configuration, CDC), and Restrictive Connected Limited Device Configuration (limited connection device configuration, CLDC). J2SE Technology Application Java 2 Standard Edition is a development and deployment platform that provides a written desktop and workstation application all necessary features. J2SE software is a preferred solution for rapid development, deployment of key tasks and corporate applications. J2SE 1.4 is developed based on Java cross-platform technology and powerful security modules, which greatly improves the scaff, flexibility, applicability, and reliability of Java language. J2SE 1.4 Features: 1. Good computational performance and zoom capabilities. J2SE 1.4 is a comprehensive platform for rapid development and configuration cross-platform enterprise-class applications and services. It enhances the performance and scaling capabilities of Java calculations, representing the big step progress in Java technology. With the J2SE version 1.4, companies can take less time through more easily steps, and use Java technology development and configuration requirements higher applications. J2SE 1.4 version has been significantly improved in Java client applications. Swing-based Java applets and applications have also improved in the response speed of the graphical user interface (GUI). 2. Cross the platform. The J2SE version 1.4 is a comprehensive platform that enables a complete, scalable high-performance application on any type of platform. 3. Support Web services. J2SE 1.4 version is compatible with previous J2SE editions. J2SE 1.4 Edition has also supported industry standard technology such as SSL, LDAP and CORBA, thus ensuring interoperability between different platforms, systems, and environments. J2SE 1.4 supports XML technology and a set of security services, so it has laid an important foundation for the creation of interoperable applications and services based on various standards. With the J2SE version 1.4 and Java Web Services Developer Pack, developers can create, test, and configure web services. 4. Integrity. J2SE 1.4 is still a complete development environment. Developers can create rich interactive applications based on this environment. These applications can be configured on any platform. J2SE 1.4 has a new GUI control function, fast Java 2DT graphics feature, supports internationalization and localization extensions and new configuration options, and provides extended support for Windows XP. In short, J2SE 1.4 version is a development basis for a variety of different style software, including client Java applets and applications, as well as separate server applications. J2SE 1.4 is also the foundation of J2ME, which is the driving force of J2EE execution. Java can develop very quickly because the Internet has developed very fast.
