Java EE learning (1)

Overview of Java EE

This is the first article of my study notes of The Java EE Tutorial

目录

用 [TOC]来生成目录：

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Overview

The aim of Java EE platform is to provide developers with a powerful set of APIs while shortening development time, reducing application complexity, and improving application performance.

• JCP: Java Community Process is responsible for all Java technologies.
• JSRs: Java Specification Requests is to define various Java EE technologies
  The work of Java Community under the JCP program helps to ensure Java technology’s standards of stability and cross-platform compatibility.

Programming model

XML deployment descriptors are optional. Instead, a developer can simply enter the information as an annotation directly into a Java source file, and the Java EE server will configure the component at deployment and runtime. These annotations are generally used to embed in a program data that would otherwise be furnished in a deployment descriptor.

Dependency injection

In the Java EE platform

• Dependency injection can be applied to all resources a component needs, effectively hiding the creation and lookup of resources from application code.
• Dependency injection can be applied to all resources a component needs, effectively hiding the creation and lookup of resources from application code.
• Dependency injection can be used in Enterprise JavaBeans(EJB) containers, web containers and application clients.
• Dependency injection allows Java EE container to automatically insert references to other required components or resources, using annotations.

Java EE Application Model

Java EE application model defines an architecture for implementing services as multitiered applications that deliver the scalability, accessibility and manageability needed by enterprise-level applications. This model partitions the work needed to implement a multitiered service into the following parts:

• The** business and presentation logic **to be implemented by the developer
• The **standard system services **provided by the Java EE platform

Distributed Multitiered Applications

The java EE application parts shown in Figure 1-1 are presented in Java EE Components

• Client-tier components run on the client machine
• Web-tier components run on the Java EE server
• Business-tier components run on the Java EE server
• Enterprise information system (EIS)-tier software runs on the EIS server

Figure 1-1 Multitiered Applications

Java EE Components

• Application clients and applets are components that run on the client
• Java Servlet, JavaServer Faces, and JavaServer Pages(JSP) technology components are web components that run on the server
• Enterprise beans (EJB) components are business components that run on the server

Java EE Clients

Usually either a web client or an application client

Web Clients

A web client consists of two parts:

• Dynamic web pages containing various types of markup language (HTML, XML, and so on), which are generated by web components running in the web server
• A web browser, which renders the pages received from the server

Application Clients

• An application client runs on a client machine and provides a way for users to handle tasks that require a richer user interface than can be provided by a markup language.
• An application client typically has a graphical usr interface(GUI) created from the Swing API or the Abstract Window Toolkit(AWT)API, but a command-line interface is certainly possible.
• Application clients directly access enterprise beans running in the business tier.
• Application clients written in languages other than Java can interact with Java EE servers, enabling the Java EE platform to interoperate with legacy systems, clients and non-java languages.

Applets

A web page received from the web tier can include an embedded applet. Written in Java programming language, an applet is a small client application that executes in the Java virtual machine installed in he web browser. However, client systems will likely need the Java Plug-in possibly a security policy file for the applet to successfully execute in the web browser.

• Web components are the preferred API for creating a web client program because no plug-ins or security policy files are needed on he client systems.
• Web components also enable cleaner and more modular application design because they provide a way to separate applications programming from web page design.

The javaBeans Component Architecture

The server and client tiers might also include components based on the javaBeans component architecture (JavaBeans components) to manage the data flow between the following:

• An application client or applet and components running on the java EE server
• Server components and a database

JavaBeans components are not considered Java EE components by the Java EE specification
JavaBeans components:

• have properties and have get and set methods for accessing those properties.
• used in this way are typically simple in design and implementation but should conform to the naming and design conventions outlined in the JavaBeans component architecture

Java EE Server Communications

Figure 1-2 Server Communication

- The client communicates with the business tier running on the Java EE server either directly or,
- as in the case of a client running in a browser, by going through web pages or servlets running in the web tier.

Web Components

Java EE web components are either servlets or web pages created using JavaServer Faces technology and/or JSP technology (JSP pages).

Figure 1-3 Web Tier and Java EE Applications

Business Components

Business code is logic that solves or meets the needs of a particular business domain, is handled by enterprise beans running in either the business tier or the web tier.

Figure 1-4 Business and EIS Tiers

Enterprise Information System Tier

It handles EIS software and includes enterprise infrastructure systems, such as enterprise resource planing (ERP), mainframe transaction processing, database systems, and other legacy information systems.

Java EE Containers

Container Services

Containter Types

Web Services Support

XML

SOAP Transport Protocol

WSDL Standard Format

Java EE Application Assembly and Deployment

Java EE 8 APIs

Java EE 8 APIs in the Java Platform, Standard Edition 8