J2EE与中间件学习概要一(overview)

企业级的应用

越来越多的开发者意识到 distributed, transactional, and portable applications 的重要性，Enterprise applications provide the business logic for an enterprise. 他们通常与其他企业级应用进行交互，我们的目的是用更少的钱、更快的速度、更少的资源来构建企业级的应用

The aim of the Java Platform, Enterprise Edition (Java EE) platform is to provide developers a powerful set of APIs while reducing development time, reducing application complexity, and improving application performance.

帮助开发者减少开发的时间，以及项目的复杂度并提高应用的性能。（提供了一系列强大的API 供开发者使用）

The Java EE platform uses a simplified programming model more annotations and less XML configuration more Plain Old Java Objects (POJOs), and simplified packaging

简化的编程模型，更多的注释，更少的XML配置，更多的POJO，简化的打包

The Java EE application model 基于Java编程语言以及JVM，它的可移植性、安全性、生产效率都比较不错
The Java EE application model defines an architecture for implementing services as multitier applications that deliver the scalability, accessibility, and manageability needed by enterprise-level applications.

当实现一项multitier service时，工作被分成了以下：
The business and presentation logic to be implemented by the developer （开发者关注业务和视图逻辑）
The standard system services provided by the Java EE platform（系统服务由Java EE platform提供）

In software engineering, multi-tier architecture (often referred to asn-tier architecture) is aclient–server architecture in which presentation, application processing, and data management functions are logically separated.

the Java EE security environment enables security constraints to be defined at deployment time

Java EE Components

The difference between Java EE components and “standard” Java classes is that Java EE components are assembled into a Java EE application, are verified to be well formed and in compliance with the Java EE specification, and are deployed to production, where they are run and managed by the Java EE server.

Java EE Clients

分为两种：

1、网页用户（轻量级用户）

2、应用程序用户（Application clients directly access enterprise beans running in the business tier）

Java EE 的WEB组件

Java EE web components are either servlets or web pages created using JavaServer Faces technology and/or JSP technology (JSP pages).
might include a JavaBeans component to manage the user input and send that input to enterprise beans running in the business tier for processing

Java EE 的Business组件

Enterprise JavaBeans (EJB) components (enterprise beans) are business components that run on the server.
Business code, which is logic that solves or meets the needs of a particular business domain such as banking, retail, or finance, is handled by enterprise beans running in either the business tier or the web tier.

Java EE 的Enterprise Information System Tier

The enterprise information system tier handles EIS software and includes enterprise infrastructure systems such as enterprise resource planning (ERP), mainframe transaction processing, database systems, and other legacy information systems.

事务的处理，数据库系统等