Introduction to Java EE Development Technology Foundation

First, the concept of Java EE

Currently, there are 3 versions of the Java 2 platform, which are Java 2 platform Micro (Java 2 Platform Micro edition,j2me) for small devices and smart cards, Java 2 Platform Standard Edition for desktop systems (Java 2 Platform Standard edition,j2se), JAVA2 Platform Enterprise Edition for creating server applications and Services (Java 2 Platform EntERPrise edition,j2ee).

Java EE is an architecture that leverages the java-based 2 platform to simplify the development, deployment, and management of enterprise solutions. Java-EE technology is based on the core of the Java platform or the standard version of 2 platform, EE not only consolidate the standard version of many of the advantages, such as "write once, run Anywhere" feature, easy access to the database JDBC API, CORBA technology and Safe mode to protect data in Internet applications, and so on, while providing EJB (Enterprise JavaBeans), Java servlets APIs, JSP (Java Server Pages) And the full support of XML technology. The ultimate goal is to become an architecture that enables enterprise developers to dramatically shorten time-to-market.

The Java EE architecture provides a middle-tier integration framework to meet the needs of applications that require high availability, reliability, and scalability without much cost. By providing a unified development platform, Java EE lowers the cost and complexity of developing multi-tier applications, provides strong support for existing application integration, fully supports Enterprise JavaBeans, has good wizards to support packaging and deployment applications, adds directory support, and enhances security. Improved performance.

Second, the advantages of the Java EE

Java EE provides a good mechanism for building a business system with scalability, flexibility and maintainability:

Retain existing IT assets: it becomes important to use investment in existing enterprise information systems, rather than to redesign the overall solution, as companies must adapt to new business needs. In this way, a server-side platform mechanism built on existing systems in a progressive (rather than radical, total negation) manner is what the company needs. The Java EE architecture can take advantage of the user's original investments, such as Bea Tuxedo, IBM CICS, IBM Encina, Inprise Visibroker, and Netscape application Server used by some companies. This may be due to the extensive industry support of Java EE and the involvement of some important ´ enterprise computing ´ domain suppliers. Each supplier offers existing customers a way to upgrade to a portable Java EE area without having to invest in obsolete investments. The existing operating system and hardware can be kept in place because the Java-EE platform's products are almost capable of running on any operating system and hardware configuration.

Efficient development: Java EE allows the company to give some common, cumbersome service-side tasks to the middleware vendor to complete. This allows developers to focus on how to create business logic and shorten development time accordingly. The advanced middleware vendors provide the following complex middleware services:

State Management Services

Allow developers to write less code, not care about how to manage state, so that program development can be completed faster.

Continuous service

Enabling developers to write applications without encoding data access logic can generate more lightweight, database-agnostic applications that are easier to develop and maintain. Distributed shared data Object Cache service-enables developers to build high-performance systems that greatly increase the scalability of the overall deployment.

Support for heterogeneous environments: Java EE can develop portable programs that are deployed in heterogeneous environments. Java-based applications do not rely on any particular operating system, middleware, hardware. Therefore, a reasonable design based on Java program can be deployed to various platforms only once. This is critical in a typical heterogeneous enterprise computing environment. The Java EE Standard also allows customers to order off-the-shelf components from Java EE-compliant third parties, deploying them into heterogeneous environments, saving the cost of developing the entire solution for themselves.

Scalability: The enterprise must choose a server-side platform that provides excellent scalability to meet the large number of new customers who operate on their systems. Java EE platform based applications can be deployed on a variety of operating systems. For example, it can be deployed to high-end UNIX and mainframe systems, which can support 64 to 256 processors at a single computer. (This is not what the NT Server can do) The suppliers in the Java EE field provide a broader load balancing strategy. Can eliminate the bottleneck in the system, allow multiple servers integrated deployment. This deployment is up to thousands of processors and enables a highly scalable system to meet the needs of future business applications.

Stable availability: A server-side platform must function 24x7 to meet the needs of corporate customers and partners. Because the Internet is global and ubiquitous, it can cause serious damage even at night as planned. If you stop unexpectedly, it will have disastrous consequences. Java EE is deployed in a reliable operating environment, and they support long-term availability. Some Java EE deployments in a Windows environment, customers can also choose a more robust operating system such as Sun Solaris, IBM os/390. The most robust operating system can achieve 99.999% availability or only 5 minutes of downtime per year. This is the ideal choice for real time business systems.

Three, four-layer model of Java EE

Java EE uses a multi-tier distributed application model, the application logic is divided into components by function, each application component is distributed on different machines according to their layer. In fact, Sun design Java-EE is designed to solve the drawbacks of the two-tier model (Client/server), in the traditional mode, the client has too much role to appear bloated, in this mode, the first deployment is easier, but difficult to upgrade or improve, scalability is not ideal, And often based on some kind of proprietary protocol? D? D is usually some kind of database protocol. It makes it very difficult to reuse business logic and interface logic. Now Java EE's multi-layer enterprise application model divides the different layers in the two-layered model into many tiers. A multi-tier application can provide a separate layer for each service, the following is a typical four-layer structure of Java EE:

Client layer components running on the client machine

Web-tier components running on the Java EE server

The business logic layer component running on the Java EE server

Enterprise Information System (EntERPrise information System) layer software running on an EIS server

Java EE application components

Java EE applications are made up of components. The Java EE component is a self-contained software unit that is assembled into a Java EE application through related classes and files and interacts with other components. The following Java EE components are defined in the Java EE specification:

Application client programs and applets are customer layer components.

The Java servlet and JavaServer Pages (JSP) are web-tier components.

Enterprise JavaBeans (EJB) is a business layer component.

Customer Layer Components

Java EE applications can be either web-based or traditional.

Web Layer component Java EE Web layer components can be JSP pages or servlets. According to the Java EE specification, static HTML pages and applets are not web-tier components. As with the customer layer, the Web layer may contain some JavaBean objects to handle user input and send the input to the enterprise bean running on the business layer for processing.

Business Layer Components

The logic of the business layer code is used to meet the needs of special business areas such as banking, retailing, finance, and processing by enterprise beans running on the business tier. The following figure shows how a enterprise bean receives data from the client, processes it (if necessary), and sends it to the EIS layer to store it in reverse.

There are three enterprise-class beans: Session beans, Entity (entity) beans, and message driven (Message-driven) beans. The session bean represents a temporary interaction with the client program. When the client program finishes executing, the session bean and related data disappear. Instead, the entity bean represents a row of persistent records in the database's table. When a client program aborts or the server shuts down, a potential service guarantees that the entity bean's data is saved. Message-driven beans combine the characteristics of session bean and JMS message listeners. Allows a business layer component to receive JMS messages asynchronously.

Enterprise Information System Layer

Enterprise Information System layer processing enterprise Information System software includes enterprise infrastructure systems such as enterprise resource Planning (ERP), mainframe transaction processing, database system, and other legacy information systems. For example, the Java EE application component may need to access the enterprise Information system for a database connection.