摘要：盡管大多數(shù)的服務(wù)器有支持腳本語(yǔ)言的插件，通過(guò)這些腳本語(yǔ)言，比如，，，可以產(chǎn)生動(dòng)態(tài)的內(nèi)容，但是服務(wù)器大多數(shù)旨在為靜態(tài)頁(yè)面服務(wù)。

??作為Java工程師，服務(wù)器對(duì)于我們的開(kāi)發(fā)工作很重要，將我們開(kāi)發(fā)好的項(xiàng)目放到服務(wù)器上用戶(hù)才可以使用。我們常用到的服務(wù)器有Tomcat、Apache、Nginx等等。對(duì)于我們所開(kāi)發(fā)的應(yīng)用，如何選擇合適的服務(wù)器是個(gè)問(wèn)題。下面簡(jiǎn)單的介紹Web服務(wù)器、Servlet容器、應(yīng)用服務(wù)器的基本概念以及各種服務(wù)器的應(yīng)用場(chǎng)景。
??本文是Google上查詢(xún)的幾遍文章的部分截?cái)啵易约杭由狭酥形姆g。

??Apache、IIS、Nginx

??Web Servers are responsible for serving static content e.g. HTML over HTTP protocol.
??Web服務(wù)器的主要職責(zé)是服務(wù)靜態(tài)頁(yè)面，例如，以HTTP協(xié)議傳輸?shù)腍TML頁(yè)面

??In a simple situation,a user type in a URL in browser(a client),and get a web page to read.So what the server does is sending a web page to the client.The transformation is in HTTP protocol which specifies the format of request and response message.
??一個(gè)簡(jiǎn)單的應(yīng)用場(chǎng)景,用戶(hù)在瀏覽器(客戶(hù)端)輸入U(xiǎn)RL并且開(kāi)始瀏覽網(wǎng)頁(yè)。那么服務(wù)器所做的就是發(fā)送一個(gè)靜態(tài)頁(yè)面到客戶(hù)端，傳輸?shù)男畔⑹峭ㄟ^(guò)指定了請(qǐng)求和響應(yīng)格式的HTTP協(xié)議。

??Tomcat、Jetty

??A servlet-container supports only the servlet API(including JSP,JSTL)
??Servlet容器僅僅支持Servlet API，包括JSP、JSTL

??Servlet container are only responsible for generating HTML by executing JSP and Servlet on Server side.So servlet container is essentially a part of a web server that interacts with the servlets.
??Servlet容器唯一的職責(zé)就是通過(guò)執(zhí)行服務(wù)器上的JSP和Servlet來(lái)產(chǎn)生HTML頁(yè)面。那么Servlet容器本質(zhì)上是Web服務(wù)器的一部分，只不過(guò)加上了和Sevlet交互的接口。

??Servlet is an interface defined in javax.servlet package.It declares three essential methods for the life cycle of a servlet – init(),service(),and destroy().They are implemented by every servlet and invoked at specific times by the server.
??Servlet是定義在javax.servlet包下面的接口。對(duì)于一個(gè)Servlet的聲明周期，它聲明了三種內(nèi)在的方法——init(),servie()和destroy().在服務(wù)器上每一個(gè)Servlet被喚醒的時(shí)候，他們都會(huì)執(zhí)行。

How Servlet Container and web server process a request ?

Web server receives HTTP request

Web server forwards the request to servlet containter

The servlet is dynamically retrieved and loaded into the address space of the container,if it is not in the container.

The container invokes the init() method of the servlet for initialization(invoked once when the servlet is loaded first time)

The container invokes the service() method of the servlet to process the HTTP request,read data in the request and formulate a response.The servlet remains in the container’s address space and can process other HTTP requests.

??WebSphere,WebLogic,JBoss

??Application Server is responsible for generating dynamic content by executing server side code e.g. JSP,Servlet or EJB.
??應(yīng)用服務(wù)的主要職責(zé)就是通過(guò)執(zhí)行服務(wù)器代碼產(chǎn)生動(dòng)態(tài)頁(yè)面，列如，JSP，Servlet或者EJB。

??Application server is responsible for serving dynamic content,managing EJB pool,facilitating distributed transation,facilitating application lookup over JNDI,application security and others.
??應(yīng)用服務(wù)器的主要任務(wù)是服務(wù)動(dòng)態(tài)內(nèi)容，管理EJB Pool，促進(jìn)事務(wù)分配，促進(jìn)應(yīng)用查找JNDI，應(yīng)用安全等等。

??An application server supports the whole JavaEE - EJB,JMS,CDI,JTA
??應(yīng)用服務(wù)器支持整個(gè)JavaEE體系
??An application usually includes a Web server,but also adds a lot of more features.The most important is that it manages objects.Whether they will be Servlets,EJBs,JMS listenters.
??一個(gè)應(yīng)用服務(wù)器通常包括一個(gè)Web服務(wù)器，但是額外加了很多特性。最重要的就是它管理對(duì)象（Servlets,EJB,JMS）

??Tomcat is not exactly an application server, it"s more of a servlet engine or web container or also known as servlet containers because it provides the runtime environment for Servlet and JSP but doesn"t provide the services like EJB and distributed transaction which are a key feature of the application server in Java JEE world
??Tomcat不完全是一個(gè)應(yīng)用服務(wù)器，它只是一個(gè)Servlet引擎或者是一個(gè)Web容器或者是我們眾所周知的Servlet容器，因?yàn)樗惶峁┝薙ervlet和JSP的運(yùn)行環(huán)境，但是沒(méi)有提供像是EJB和事務(wù)控制的部分，而這部分才是JEE領(lǐng)域里面應(yīng)用服務(wù)器的特點(diǎn)。

??It’s expected from a Web server to provide HTTP protocol level service while application server is supposed to provide more powerful and dynamic Web service and business level service via EJB(Enterprise Java Beans).Essential services like Database connection pooling is not only provided by application server but also by Servlet containers like Tomcat.
??可以預(yù)計(jì)的是一個(gè)Web服務(wù)器提供HTTP協(xié)議層次的服務(wù)，應(yīng)用服務(wù)器應(yīng)該是提供更多的強(qiáng)大的動(dòng)態(tài)的Web服務(wù)，并且包括商務(wù)級(jí)別的服務(wù)經(jīng)由EJB。像數(shù)據(jù)庫(kù)連接池這樣必要的服務(wù)不僅僅是應(yīng)用服務(wù)器支持，像是Tomcat這樣的Servlet容器也支持。

??You need a Web server like Apache HTTPD if you are serving static web pages.If you have a Java application with just JSP and Servlet to generate dynamic content then you need Servlet containers like Tomcat or Jetty while,if you have JavaEE application using EJB,distributed transation,messaging and other fancy features than you need a full fledged application server like JBoss,WebSphere or WebLogic.
??如果你為靜態(tài)頁(yè)面提供服務(wù)，你就需要像Apache HTTPD這樣的Web服務(wù)器。如果你有一個(gè)僅僅是JSP和Servlet的JAVA應(yīng)用去生成動(dòng)態(tài)的頁(yè)面內(nèi)容，你需要一個(gè)像Tomcat或者Jetty這樣的Servlet容器。如果你的JAVAEE應(yīng)用使用了EJB，事務(wù)管理，消息和其他一些復(fù)雜華麗的特點(diǎn)，你就需要一個(gè)完全成熟的應(yīng)用服務(wù)器，列如JBoss，WebSphere或者WebLogic.

??For example,one of the popular setups is Apache fronting Tomcat or Ngnix fronting Tomcat
??比如，一個(gè)非常流行的做法就是在Tomcat上面加一Apache或者是在Tomcat上加Nginx服務(wù)。

??What is the difference between application server and web server ?

??Web Server is designed to serve HTTP Content. Application Server can also serve HTTP Content but is not limited to just HTTP. It can be provided other protocol support such as RMI/RPC
??Web服務(wù)器旨在為HTTP內(nèi)容提供服務(wù)。應(yīng)用服務(wù)器也可以為HTTP內(nèi)容提供服務(wù)，但是它不僅僅限于HTTP，它可以提供其他的協(xié)議支持，例如RMI/RPC。

??Web Server is mostly designed to serve static content, though most Web Servers have plugins to support scripting languages like Perl, PHP, ASP, JSP etc. through which these servers can generate dynamic HTTP content.
??盡管大多數(shù)的Web服務(wù)器有支持腳本語(yǔ)言的插件，通過(guò)這些腳本語(yǔ)言，比如PHP，ASP，JSP，可以產(chǎn)生動(dòng)態(tài)的HTTP內(nèi)容，但是Web服務(wù)器大多數(shù)旨在為靜態(tài)頁(yè)面服務(wù)。

??Most of the application servers have Web Server as integral part of them, that means App Server can do whatever Web Server is capable of. Additionally Application Server have components and features to support Application level services such as Connection Pooling, Object Pooling, Transaction Support, Messaging services etc.
??大多數(shù)的應(yīng)用服務(wù)器都包括Web服務(wù)器來(lái)構(gòu)成他們完整的體系，這也就意味著應(yīng)用服務(wù)器可以做任何Web服務(wù)器有能力做的事情。除此之外，應(yīng)用服務(wù)器包含了一些能夠達(dá)到應(yīng)用層次的組件和特點(diǎn)，例如連接池，對(duì)象池，事務(wù)支持，消息服務(wù)等。

??As web servers are well suited for static content and app servers for dynamic content, most of the production environments have web server acting as reverse proxy to app server. That means while service a page request, static contents such as images/Static html is served by web server that interprets the request. Using some kind of filtering technique (mostly extension of requested resource) web server identifies dynamic content request and transparently forwards to app serve
??對(duì)于靜態(tài)頁(yè)面來(lái)說(shuō)Web服務(wù)器很適，而應(yīng)用服務(wù)器適合動(dòng)態(tài)內(nèi)容，但是大多數(shù)的生產(chǎn)環(huán)境都是有一個(gè)Web服務(wù)器作為應(yīng)用服務(wù)器的反向代理。這就意味著一個(gè)頁(yè)面的請(qǐng)求，像圖片和靜態(tài)HTML這樣的靜態(tài)內(nèi)容是由Web服務(wù)器提供服務(wù)。使用一些像過(guò)濾器這樣的技術(shù)，Web服務(wù)器鑒別動(dòng)態(tài)內(nèi)容請(qǐng)求并顯示的導(dǎo)向應(yīng)用服務(wù)器。