huatij2ee简介毕业论文外文文献翻译

2020年12月30日发(作者：柏扬)
英文原文：

J2EE synopsis:


J2EE is a set is completely different in the traditional application development
technical frame, contains many modules, mainly may simplify, and the standard
application system's development and the deployment, then enhance the probability,
the security and use the value again.
The J2EE core is a group of technology standard and the guide, contains each
kind of module, the service construction and the technical level, has the common
standard and the specification, lets each kind rely on the J2EE construction between
the different platform, has the good compatibility, between information product each
other who the solution behind the enterprise used in the past is unable compatibly, the
enterprise interior or exterior exchanged with difficulty predicament.
At present, the Java 2 platforms have 3 editions, they are suitable for the
bantam and smart card Java 2 platform Micro version (Java 2 Platform Micro Edition,
J2ME), are suitable for the tabletop system's Java 2 platform standard edition (Java 2
Platform Standard Edition, J2SE), are suitable for the foundation server application
procedure and the service Java 2 platform enterprise version (Java 2 Platform
Enterprise Edition, J2EE).
J2EE is one kind simplifies the enterprise solution using the Java 2 platforms
the development, the deployment and the management related complex question
architecture. The J2EE technology's foundation was the core Java platform or the Java
2 platform standard edition, J2EE has not only consolidated in standard edition many
merits, for example compiled one time, everywhere moved the characteristic,
convenience deposit database JDBC API, the CORBA technology as well as can in
the Internet application protect data safe mode and so on, meanwhile has provided to
EJB (Enterprise JavaBeans), Java Servlets API, JSP (Java Server Pages) as well as the
XML technology comprehensive support. Its final goal is becomes one to be able to
cause the enterprise exploiters to reduce largely puts in the market hour the
architecture.
The J2EE architecture provides the intermediate level integration frame to use
for not to need too many expenses satisfiedly and to need the high usability, the
redundant reliability as well as the extendibility application demand. Through provided
the unification the development platform, J2EE reduced the development multi-layer
application expense and the complexity, simultaneously provided to the existing
application procedure integrates the powerful support, supported Enterprise JavaBeans
completely, had the good guide to support packs and deploys the application, the
increase table of contents support, strengthened the safety mechanism, enhanced the
performance.
The J2EE to building have scalability, flexibility, easy maintenance business
system provides a good mechanism:
1. Retain existing IT assets: because enterprise must adapt to the new
commercial demand, by means of the existing enterprise information system in
investment, rather than re-enacted overall scheme is very important. So, a gradual (not
radical, completely negative) way above the existing system established the server
platform mechanism is not fair that the company needs. Can make full use of the user
J2EE, as some of the original investment companies use the Tuxedo, IBM CICS BEA,
IBM VisiBroker Inprise Encina,, and Netscape apply Server. This is possible because
the J2EE extensive industry supported and some important 'enterprise computing'
field supplier to participate. Each supplier to existing customer provides no
abandoned existing investment into portable J2EE field upgrade path. Based on the
J2EE platform because the product can almost in any operating system and hardware
configurations to run on existing operating system and hardware can also be retained
use.
2. Efficient development: the J2EE allows companies to some generic, very
tedious tasks to a server to complete the middleware vendors. So that developers can
focus on how to create business logic, correspondingly shorten the development time.
Senior middleware vendors provide the following these complex middleware
services:
。State management service -- let developers to write less code, don't care about
how to manage state, so can complete application development faster.
。Persistent services - lets developers don't have to encode data access logic can
write applications that can generate a lighter, and database irrelevant applications, this
application easier to development and maintenance.
。Distributed share data object CACHE service -- let development staffing
high-performance systems, greatly enhance the loft deployment.
t heterogeneous environment: the J2EE can develop the heterogeneous
environment can be deployed in transplant programs. Based on the J2EE application
is not dependent on any specific operating system, middleware, hardware. So the
reasonable design based on J2EE program just can be deployed to develop a various
platforms. This in a typical heterogeneous enterprise computing environment is very
critical. The J2EE standard also allows customers to order and J2EE compatible
third- party ready-made components, put them to deploy on heterogeneous
environment, save by oneself make of the cost of the whole scheme.
4. Scalability: enterprise must choose a server not fair Taiwan, the platform
should be able to offer excellent scalability to satisfy those in their system on the large
number of new customers of commercial operation. Based on the J2EE platform
application can be deployed to all operating systems. For example can be deployed to
high-end UNIX and mainframe systems, this system can support single 64 to 256
processor. (this is exceed NT server supplier of the) J2EE field provides a more
extensive load balancing strategy. Can eliminate system bottlenecks, allow multiple
servers integration to deploy. The deployment of thousands of processors, realize
flexible system, highly satisfied future commercial application needs.
5. Stable usability: a server platform must be able to round-the-clock operation
not fair to meet the needs of our customers, partners. Because the INTERNET is the
globalization, everywhere, even at night as planned downtime also may cause serious
damage. If it hangs, it will have disastrous consequences. The J2EE deployed to
reliable operating environment, they support long-term usability. Some J2EE
deployed in WINDOWS environment, customers also can choose to robust
performance better operating systems such as from Solaris, IBM OS 390. The most
robust operating system can achieve 99.999% availability or just 5 minutes downtime
every year. This is real-time strong business system ideal choice.
J2EE four layers model
The J2EE multilayer distributed applications used by function, application
logic model into components, each application components according to their shape
layer distribution in different machine. In fact, from the original intention is to design
the J2EE solve two layer mode (are) server the disadvantages of traditional mode, in
client bear too many roles and appear bloated, in this mode, the first deployment, but
difficult to compare easy when upgrade or improved, scalability, and often not ideal
based on some proprietary agreement is usually some kind of database agreement. It
makes reuse business logic and interface logic is very difficult. Now the J2EE
multilayer the enterprise applications model of two layer of the model different levels
cut into many layers. A DuoCengHua application for different each service to provide
a separate layer, the following is typical of the four layers J2EE structure:

。Running on a client machine customer layer components
。Run on J2EE server Web layer components
。Run in the business logic of the J2EE server layer components
。On a server running on EIS Enterprise information system (Enterprise information
system) layer of software below is typical of the four layers J2EE structure:


The J2EE application components
The J2EE application is by components. The J2EE is a separate function of
component software units, which passed the relevant classes and file assemble J2EE
application, and with other component interaction. The J2EE specification of J2EE
defined in the following components:
。Application client program and applets is customer layer components.
。Java Servlet and JavaServer web (JSP) is web layer components.
。Enterprise JavaBeans (EJB) is a business layer components.
Customer layer components
Based on J2EE application can be a web form, also can be based on the
traditional way.
Web layer components
The J2EE web layer components can be the JSP page or Servlets. According
to the J2EE specification, static HTML pages and Applets isn't web layer components.
As the chart shows, the customer layer that web layer may contain some JavaBean
object to handle user input, and send to run in the input of bean enterprise business
layer to undertake handling.

Business layer components
Business layer code used to satisfy Banks, retail logic, finance and other special
business areas in need, by operation of enterprise business layer process. The figure
below shows the bean bean is a enterprise how receiving data from the client program,
undertake handling (if necessary), concurrent to EIS layer stored, this process can also
reverse.
There are three kinds of enterprise-level bean: session (session) beans beans,
the entity (entity), and message driver (< - driven) bean said beans. The conversation
with the client program. When the temporary interaction after client program
execution, bean and related data session will disappear. Instead, entity bean said
database table ever recorded in line. When the client program suspended or closed
servers, you will have the potential of service guarantees entity to preserve the data
bean bean. News drive combines the bean and JMS news session the characteristics of
listeners, allowing a business layer component asynchronous receiving JMS news.


The enterprise information system layer
The enterprise information system layer processing enterprise information
system software including enterprise infrastructure system such as enterprise resource
planning (ERP), mainframe transaction processing, database system, and other legacy
information system. For example, J2EE application components can in order to
database connections need access to the enterprise information system
The J2EE structure
This based on components have platform-independent characteristics of J2EE
structure makes the J2EE program is very simple, because the writing business logic
being sealed into reusable components, and the form of J2EE server to container for
all component types provide backend service. Because you don't have to develop their
own this service, so you can focus on solving business problems.
Containers and service
Containers set custom made J2EE server inner support provided, including
safety, business management, JNDI (Java Naming and Directory addressing, with)
services such as remote connection, the most important listed below several services
。The J2EE safety (Security) model can let you to configure the web components
or enterprise bean, so that only authorized users can access system resources. Each
customer belong to a special role, and every character only allow activate a particular
method. You should be in enterprise bean decorate description characters and can be
activated statement of the method. Because of this statement sex, you don't have to
write strengthening methods of safety rules.
。The J2EE affairs Management (Transaction Management) model allows you to
specify a affairs of the relationship between all methods, such a affairs as all the way
to a single unit. When the client activate a bean and the method of enterprise
Management affairs container intervention. For a container management in enterprise
bean in affairs, you don't have to encode affairs of the border. The code distributed
transactions required control will be very complicated. You need only to decorate
documents state enterprise bean described the transaction attribute, instead of writing
and debug complex code. Will be read this document and container for you deal with
this enterprise bean affairs
。JNDI addressing (JNDI Lookup) services to the business enterprise inside
multiple names and directory services provide a unified interface, such application
component can access names and directory services.
。The J2EE Remote connections (Remote login) model management are enterprise
between Client and the lower the bean bean interaction. When a enterprise after
creation, a Client can call it methods like it and Client as in the same virtual machine.
。Survival Cycle Management (act enterprise Management) model Management pa
bean created and removed, a enterprise bean in its survival Cycle will be after several
state. Container enterprise bean, and create instances pool and activities in the
available, and state of will eventually move him removed from the vessel. Even if can
call the enterprise bean remove method, and create containers will also carry out these
tasks in the background.
。Database Connection pool (Database Connection Pooling) model is a valuable
resource. Access database connection is a time-consuming work, and number of
connections is very limited. Containers through management to reduce these problems
connection pool. Bean enterprise from the pool quick access connections. In the
release of bean bean for other connected use. Bean's affairs.
Vessel types
The J2EE application components can be installed to deploy on several
containers to:
。EJB container management all the J2EE application of enterprise bean
enterprise- level bean and their implementation. The containers run on J2EE server.
。Web container management all the J2EE application JSP page and Servlet
component execution. Web components and their containers run on J2EE server.
。Application client container management all the J2EE application applications
client component of execution. Application client and their containers run on J2EE
server.
。Applet container is running on a client machine web browser plugin and Java
combination.




The core API and J2EE components
The J2EE platform by a set of service (Services for), application program
interface (APIs) and agreement constitutes for development based on Web, it provides
the functions of multi-layer application support, the 13 to J2EE specification for
simple description (somewhere here only simple description) :
1. JDBC Database (Java login) : JDBC API for visit different Database provides a
unified approach, like the same, JDBC to developers by ODBC shielding some detail
problems, in addition, JDCB the Database access also have platform-independent
characteristics.
2. JNDI (Java Name and Directory JNDI API with) : by Name and Directory
service for execution. It provides a consistent model to access and operation of
enterprise-level resources such as DNS and LDAP, local file systems, or application
server objects.
3. The EJB (Enterprise JavaBean) : J2EE technology is a body of won wide
attention isand EJB to reach the same goal.
4. RMI (Remote Invoke) : as of as its name suggests, the Remote object RMI
agreement calls Method. It USES the serialized way in client and server transfer data.
RMI is being used more at the bottom of the EJB agreement.
5. Java IDLCORBA: in Java (IDL, under the support of the developers can will
Java and CORBA integrated together. They can create Java objects and carried in
CORBA, ORB or they can create Java classes and as and other ORB of CORBA
object launched with clients. After a kind of method provides another kin one of the
reasons the EJB. They provide a framework to develop and implement business logic,
which is distributed significantly simplified have scalability and highly complex
enterprise applications development. EJB standard defines how and when EJB
components of their vessels interaction. Container is responsible for providing public
services, such as directory services, business management, safety, resources buffer
pool and fault tolerance. But here, it is worth noting, EJB is not the only way to
realize the J2EE. Because the openness, makes some J2EE with a firm can parallel
manner d of way, by which it Java can be used to put your new applications and the
old system combined.
6. The JSP (Java Server web) : the JSP page from the HTML code and the Java
code embedded them together. Server in a page is the client requested to these Java
code after processed and then will generate the HTML page back to the client
browser.
7. Java Servlet: Servlet is a small Java program, it expanded the Web server
functions. As a server-side application, when requested started, this and CGI Perl
script very similar. The function is mostly Servlet provide with JSP similar, but
different implementation. The JSP are usually most HTML code embedded in a small
amount of Java code, and servlets all written by Java and generating HTML.
8. XML (Extensible creating Language) : XML is a can be used to define other
Markup Language Language. It is used in different business process share data. XML
development and Java is independent of each other, but it has the same goal and Java
is platform independence. Through the combination will Java and XML, you can get a
perfect has platform independence solutions.
9. JMS (Java macro Service) : MS is used to and facing the Message oriented
middleware mutual communication application program interface (API). It supports
both point-to-point domain, a support publishsubscribe (publishby the domain) type,
and to provide the following types of support: approved message transfer, the
transmission, consistency non- business messages with persistent subscriber
information and support. JMS also provides another way for you to the application
and the old backend system combined.
10. JTA (Java Architecture) : Transaction JTA defines a standard API, application
system which can access various affairs monitoring.
11. JTS (Java Transaction Service) : JTS is CORBA basic offer OTS affairs
monitoring achieved. JTS stipulated affairs manager's realization. The affairs manager
is in high-level support Java Transaction JTA) standard (API, and realize the OMG
specification is bottom of Java image offer OTS. JTS affairs manager for application
server, resource manager, independent application and communication resource
manager provides services.
12. JavaMail: JavaMail is used to access E-mail server API, it provides a set of
mail server's abstract classes. Not only support SMTP server, also support IMAP
server.
13. JTA (JavaBeans Activation Framework) : JavaMail JAF to handle MIME
coding using the E-mail attachments. MIME word throttling can be converted into
Java objects, or convert from Java objects. Most applications can need not use directly
JAF.

中文译文：
J2EE简介：

J2EE是一套全然不同于传统应用的开发的技术框架，包含许多组 件，主要
可简化且规范应用系统的开发与部署，进而提高可移植性、安全与再用价值。
J2EE核心是一组技术规范与指南，其中所包含的各类组件、服务架构及技
术层次，均有共通的标准及 规格，让各种依循J2EE架构的不同平台之间，存在
良好的兼容性，解决过去企业后端使用的信息产品 彼此之间无法兼容，企业内部
或外部难以互通的窘境。
目前，Java 2平台有3个版本，它们是适用于小型设备和智能卡的Java 2平台Micro版
（Java 2 Platform Micro Edition，J2ME）、适用于桌面系统的Java 2平台标准版（Java 2
Platform Standard Edition，J2SE）、适用于创建服务器应用程序和服务的Java 2平台企业版
（Java 2 Platform Enterprise Edition，J2EE）。

J2EE是一种利用Java 2平台来简化企业解决方案的开发、部署和管理相关
的复杂问题 的体系结构。J2EE技术的基础就是核心Java平台或Java 2平台的
标准版，J2EE不仅巩 固了标准版中的许多优点，例如编写一次、随处运行的
特性、方便存取数据库的JDBC API、CORBA技术以及能够在Internet应用中保
护数据的安全模式等等，同时还提供了对 EJB（Enterprise JavaBeans）、Java
Servlets API、JSP（Java Server Pages）以及XML技术的全面支持。其最终目
的就是 成为一个能够使企业开发者大幅缩短投放市场时间的体系结构。
J2EE体系结构提供中间层集成框架 用来满足无需太多费用而又需要高可用
性、高可靠性以及可扩展性的应用的需求。通过提供统一的开发平 台，J2EE降
低了开发多层应用的费用和复杂性，同时提供对现有应用程序集成强有力支持，
完全支持Enterprise JavaBeans，有良好的向导支持打包和部署应用，添加目
录支 持，增强了安全机制，提高了性能。
J2EE为搭建具有可伸缩性、灵活性、易维护性的商务系统提供了良好的机制:
1. 保留现存的IT资产: 由于企业必须适应新的商业需求，利用已有的企业信息
系统方面的投资，而不是 重新制定全盘方案就变得很重要。这样，一个以渐
进的（而不是激进的，全盘否定的）方式建立在已有系 统之上的服务器端平
台机制是公司所需求的。J2EE架构可以充分利用用户原有的投资，如一些公司使用的BEA Tuxedo、IBM CICS, IBM Encina,、Inprise VisiBroker 以及
Netscape Application Server。这之所以成 为可能是因为J2EE拥有广泛的
业界支持和一些重要的'企业计算'领域供应商的参与。每一个供应商 都对现
有的客户提供了不用废弃已有投资，进入可移植的J2EE领域的升级途径。由
于基于J 2EE平台的产品几乎能够在任何操作系统和硬件配置上运行，现有的
操作系统和硬件也能被保留使用。
2. 高效的开发: J2EE允许公司把一些通用的、很繁琐的服务端任务交给中间件
供应商 去完成。这样开发人员可以集中精力在如何创建商业逻辑上，相应地
缩短了开发时间。高级中间件供应商 提供以下这些复杂的中间件服务:
o
状态管理服务 -- 让开发人员写更少的代码，不用关心如何管理状态，
这样能够更快地完成程序开发。
o
持续性服务 -- 让开发人员不用对数据访问逻辑进行编码就能编写应
用程序，能生成更轻巧 ，与数据库无关的应用程序，这种应用程序更
易于开发与维护。
o
分布式共享数据对象CACHE服务 -- 让开发人员编制高性能的系统，
极大提高整体部署的伸缩性。
3. 支持异构环境: J2 EE能够开发部署在异构环境中的可移植程序。基于J2EE
的应用程序不依赖任何特定操作系统、中间 件、硬件。因此设计合理的基于
J2EE的程序只需开发一次就可部署到各种平台。这在典型的异构企业 计算环
境中是十分关键的。J2EE标准也允许客户订购与J2EE兼容的第三方的现成
的组件 ，把他们部署到异构环境中，节省了由自己制订整个方案所需的费用。
4. 可伸缩性: 企业必须 要选择一种服务器端平台，这种平台应能提供极佳的可
伸缩性去满足那些在他们系统上进行商业运作的大 批新客户。基于J2EE平台
的应用程序可被部署到各种操作系统上。例如可被部署到高端UNIX与大 型机
系统，这种系统单机可支持64至256个处理器。（这是NT服务器所望尘莫
及的）J2 EE领域的供应商提供了更为广泛的负载平衡策略。能消除系统中的
瓶颈，允许多台服务器集成部署。这 种部署可达数千个处理器，实现可高度
伸缩的系统，满足未来商业应用的需要。
5.
稳定的可用性: 一个服务器端平台必须能全天候运转以满足公司客户、合作伙伴的需要。
因为 INTERNET是全球化的、无处不在的，即使在夜间按计划停机也可能造成严重损
失。若是意外停机 ，那会有灾难性后果。J2EE部署到可靠的操作环境中，他们支持长
期的可用性。一些J2EE部署在 WINDOWS环境中，客户也可选择健壮性能更好的操作
系统如Sun Solaris、IBM O S390。最健壮的操作系统可达到99.999%的可用性或每年只
需5分钟停机时间。这是实时性很 强商业系统理想的选择。

J2EE 的四层模型
J2EE使用多层的分布式应用模 型，应用逻辑按功能划分为组件，各个应用
组件根据他们所在的层分布在不同的机器上。事实上，sun 设计J2EE的初衷正
是为了解决两层模式(clientserver)的弊端，在传统模式中，客户 端担当了过
多的角色而显得臃肿，在这种模式中，第一次部署的时候比较容易，但难于升级
或改 进，可伸展性也不理想，而且经常基于某种专有的协议?D?D通常是某种
数据库协议。它使得重用业务 逻辑和界面逻辑非常困难。现在J2EE 的多层企业
级应用模型将两层化模型中的不同层面切分成许多 层。一个多层化应用能够为不
同的每种服务提供一个独立的层，以下是 J2EE 典型的四层结构:
?
?
?
?
运行在客户端机器上的客户层组件
运行在J2EE服务器上的Web层组件
运行在J2EE服务器上的业务逻辑层组件
运行在EIS服务器上的企业信息系统(Enterprise information system)
层软件

J2EE应用程序组件
J2EE应用程序是 由组件构成的.J2EE组件是具有独立功能的软件单元，它们
通过相关的类和文件组装成J2EE应用 程序，并与其他组件交互。J2EE说明书中
定义了以下的J2EE组件:
?
?
?
应用客户端程序和applets是客户层组件.
Java Servlet和JavaServer Pages(JSP)是web层组件.
Enterprise JavaBeans(EJB)是业务层组件.
客户层组件
J2EE应用程序可以是基于web方式的,也可以是基于传统方式的.
web 层组件
J2EE web层组件可以是JSP 页面或Servlets.按照J2EE规范，静态的HTML
页面和Applets不算是web层组件。
正如下图所示的客户层那样，web层可能包含某些 JavaBean 对象来处理用
户输入，并把输入发送给运行在业务层上的enterprise bean 来进行处理。

业务层组件
业务层代码的逻辑用来满足银行，零售，金融等特殊 商务领域的需要,由运
行在业务层上的enterprise bean 进行处理. 下图表明了一个enterprise bean
是如何从客户端程序接收数据，进行处理(如果必要的话), 并发送到EIS 层储
存的，这个过程也可以逆向进行。
有三种企业级的bean: 会话(session) beans, 实体(entity) beans, 和消息驱
动(message-driven) beans. 会话bean 表示与客户端程序的临时交互. 当客户
端程序执行完后, 会话bean 和相关数据就会消失. 相反, 实体bean 表示数据
库的表中一行永久的记录. 当客户端程序中止或服务器关闭时, 就会有潜在的
服务保证实体bean 的数据得以保存.消息驱动 bean 结合了会话bean 和 JMS
的消息监听器的特性, 允许一个业务层组件异步接收JMS 消息.
企业信息系统层
企业信息系统层处理企业信息系统软件包括企业基础建设系统例如企业
资源计划 (ERP), 大型机事务处理, 数据库系统,和其它的遗留信息系统. 例
如，J2EE 应用组件可能为了数据库连接需要访问企业信息系统
J2EE 的结构
这种基于组件，具有平台无关性的J2EE 结构使得J2EE 程序的编写十分简
单，因为业务逻辑被封装成可复用的组件，并且J2EE 服务器以容器的形式为所
有的组件类型提供后台服务. 因为你不用自己开发这种服务, 所以你可以集中
精力解决手头的业务问题.
容器和服务
容器设置定制了J2EE服务器所提供得内在支持，包括安全，事务管理，
JNDI(Java Naming and Directory Interface)寻址,远程连接等服务，以下列出
最重要的几种服务：
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J2EE安全(Security)模型可以让你配置 web 组件或enterprise bean ,
这样只有被授权的用户才能访问系统资源. 每一客户属于一个特别的角
色，而每个角色只允许激活特定的方法。你应在enterprise be an的布置
描述中声明角色和可被激活的方法。由于这种声明性的方法，你不必编写
加强安全性 的规则。
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J2EE 事务管理（Transaction Management）模 型让你指定组成一个事务
中所有方法间的关系，这样一个事务中的所有方法被当成一个单一的单元.
当客户端激活一个enterprise bean中的方法，容器介入一管理事务。因
有容器管理事务，在enterprise bean中不 必对事务的边界进行编码。要
求控制分布式事务的代码会非常复杂。你只需在布置描述文件中声明
enterprise bean的事务属性，而不用编写并调试复杂的代码。容器将读
此文件并为你 处理此enterprise bean的事务。
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JNDI 寻址(JNDI Loo kup)服务向企业内的多重名字和目录服务提供了一
个统一的接口,这样应用程序组件可以访问名字和 目录服务.
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J2EE远程连接（Remote Client Connectivity）模型管理客户端和
enterprise bean间的低层交互. 当一个enterprise bean创建后, 一个
客户端可以调用它的方法就象它和客户端位于同一虚拟机上一样.
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生存周期管理（Life Cycle Management）模型管理enterprise bean的
创建和移除,一个enterprise bean在其生存周期中将会历经几种状态。
容器创建enterprise bean，并在可用实例 池与活动状态中移动他，而最
终将其从容器中移除。即使可以调用enterprise bean的create及remove
方法，容器也将会在后台执行这些任务。
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数据库连接池（Database Connection Pooling）模型是一个有价值的资< br>源。获取数据库连接是一项耗时的工作，而且连接数非常有限。容器通过
管理连接池来缓和这些问 题。enterprise bean可从池中迅速获取连接。
在bean释放连接之可为其他bean使用。
容器类型
J2EE应用组件可以安装部署到以下几种容器中去:
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EJB 容器管理所有J2EE 应用程序中企业级bean 的执行. enterprise
bean 和它们的容器运行在J2EE 服务器上.
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Web 容器管理所有J2EE 应用程序中JSP页面和Servlet组件的执行. Web
组件和它们的容器运行在J2EE 服务器上.
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应用程序客户端容器管理所有J2EE应用程序中应用程序客户端组件的执
行. 应用程序客户端和它们的容器运行在J2EE 服务器上.
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Applet 容器是运行在客户端机器上的web浏览器和 Java 插件的结合.



J2EE的核心API与组件
J2EE平台由一整套服务（Services）、应用程序接 口（APIs）和协议构成，
它对开发基于Web的多层应用提供了功能支持，下面对J2EE中的13 种技术规范
进行简单的描述(限于篇幅，这里只能进行简单的描述):
1. JDBC(Java Database Connectivity): JDBC API为访问不同的数据 库提
供了一种统一的途径，象ODBC一样，JDBC对开发者屏蔽了一些细节问题，
另外，J DCB对数据库的访问也具有平台无关性。
2. JNDI(Java Name and Directory Interface): JNDI API被用于执行名字
和目录服务。它提供 了一致的模型来存取和操作企业级的资源如DNS和
LDAP，本地文件系统，或应用服务器中的对象。
3. EJB(Enterprise JavaBean): J2EE技术之所以赢得某体广泛重视 的原因
之一就是EJB。它们提供了一个框架来开发和实施分布式商务逻辑，由此
很显著地简化 了具有可伸缩性和高度复杂的企业级应用的开发。EJB规范
定义了EJB组件在何时如何与它们的容器 进行交互作用。容器负责提供公
用的服务，例如目录服务、事务管理、安全性、资源缓冲池以及容错性。
但这里值得注意的是，EJB并不是实现J2EE的唯一途径。正是由于J2EE
的开放性，使 得有的厂商能够以一种和EJB平行的方式来达到同样的目
的。
4. RMI(Remote Method Invoke): 正如其名字所表示的那样，RMI协议调用
远程对象上方法。它使用了序列化方式在客户端和服务器端传递数据。RMI
是一种被EJB使用的更底 层的协议。
5. Java IDLCORBA: 在Java IDL的支持下，开发人员可以将 Java和CORBA
集成在一起。他们可以创建Java对象并使之可在CORBA ORB中展开, 或
者他们还可以创建Java类并作为和其它ORB一起展开的CORBA对象的客
户。后一种 方法提供了另外一种途径，通过它Java可以被用于将你的新
的应用和旧的系统相集成。
6. JSP(Java Server Pages): JSP页面由HTML代码和嵌入其中的J ava代码
所组成。服务器在页面被客户端所请求以后对这些Java代码进行处理，
然后将生 成的HTML页面返回给客户端的浏览器。
7. Java Servlet: Servlet是 一种小型的Java程序，它扩展了Web服务器
的功能。作为一种服务器端的应用，当被请求时开始执 行，这和CGI Perl
脚本很相似。Servlet提供的功能大多与JSP类似，不过实现的方式 不同。
JSP通常是大多数HTML代码中嵌入少量的Java代码，而servlets全部
由Java写成并且生成HTML。
8. XML(Extensible Markup Language): XML是一种可以用来定义其它标记
语言的语言。它被用来在不同的商务过程中 共享数据。XML的发展和Java
是相互独立的，但是，它和Java具有的相同目标正是平台独立性 。通过
将Java和XML的组合，您可以得到一个完美的具有平台独立性的解决方
案。
9. JMS(Java Message Service): MS是用于和面向消息的中间件相互 通信的
应用程序接口(API)。它既支持点对点的域，有支持发布订阅
(publishsu bscribe)类型的域，并且提供对下列类型的支持：经认可的
消息传递,事务型消息的传递，一致 性消息和具有持久性的订阅者支持。
JMS还提供了另一种方式来对您的应用与旧的后台系统相集成。
(Java Transaction Architecture): JTA定义了一种标准的API，应
用系统由此可以访问各种事务监控。
(Java Transaction Service): JTS是CORBA OTS事务监控的基本的
实现。 JTS规定了事务管理器的实现方式。该事务管理器是在高层支持
Java Transaction API (JTA)规范，并且在较底层实现OMG OTS
specification的Java 映像。JTS事务管理器为应用服务器、资源管理器、
独立的应用以及通信资源管理器提供了事务服务。
il: JavaMail是用于存取邮件服务器的API，它提供了一套邮件服
务器的抽象类 。不仅支持SMTP服务器，也支持IMAP服务器。
JTA(JavaBeans Activation Framework): JavaMail利用JAF来处理MIME
编码的 邮件附件。MIME的字节流可以被转换成Java对象，或者转换自Java对
象。大多数应用都可以 不需要直接使用JAF。