Servlet是什么
為了能讓W(xué)eb服務(wù)器與Web應(yīng)用這兩個不同的軟件系統(tǒng)協(xié)作，需要一套標(biāo)準(zhǔn)接口，Servlet就是其中最主要的一個接口。
規(guī)定：
Web服務(wù)器可以訪問任意一個Web應(yīng)用中實(shí)現(xiàn)Servlet接口的類。
Web應(yīng)用中用于被Web服務(wù)器動態(tài)調(diào)用的程序代碼位于Servlet接口的實(shí)現(xiàn)類中。
SUN公司（現(xiàn)在被Oracle收購了……）制定了Web應(yīng)用于Web服務(wù)器進(jìn)行協(xié)作的一系列標(biāo)準(zhǔn)Java接口（統(tǒng)稱為Java Servlet API）。
SUN公司還對Web服務(wù)器發(fā)布及運(yùn)行Web應(yīng)用的一些細(xì)節(jié)做了規(guī)約。SUN公司把這一系列標(biāo)準(zhǔn)Java接口和規(guī)約統(tǒng)稱為Servlet規(guī)范。
Servlet是一種運(yùn)行在服務(wù)器上的小插件。
Servlet容器是什么
在Servlet規(guī)范中，把能夠發(fā)布和運(yùn)行JavaWeb應(yīng)用的Web服務(wù)器稱為Servlet容器，他的最主要特稱是動態(tài)執(zhí)行JavaWeb應(yīng)用中的Servlet實(shí)現(xiàn)類中的程序代碼。
Tomcat是什么
Tomcat是Servlet容器，同時也是輕量級的Web服務(wù)器。
Apache Server、Microsoft IIS、Apache Tomcat都是Web服務(wù)器。
Tomcat作為Web服務(wù)器時，主要負(fù)責(zé)實(shí)現(xiàn)HTTP傳輸?shù)裙ぷ鳌?/p>
Tomcat作為Servlet容器時，主要負(fù)責(zé)解析Request，生成ServletRequest、ServletResponse，將其傳給相應(yīng)的Servlet（調(diào)用service( )方法），再將Servlet的相應(yīng)結(jié)果返回。
Tomcat組成結(jié)構(gòu)
Server，代表整個Servlet容器組件，是Tomcat的頂層元素。其中可以包含一到多個Service；
Service，包含一個Engine，以及一到多個Connector；
Connector，代表和客戶端程序?qū)嶋H交互的組件，負(fù)責(zé)接收客戶請求，以及向客戶返回響應(yīng)結(jié)果；
Engine，處理同一個Service中所有Connector接收到的客戶請求；
Host，在Engine中可以包含多個Host，每個Host定義了一個虛擬主機(jī)，它可以包含一個到多個Web應(yīng)用；
Context，一個Host中可以包含多個Context，每個Context代表了運(yùn)行在虛擬主機(jī)上的單個Web應(yīng)用。
這些字段都在conf/server.xml中配置，下面是一段apache tomcat 6.0.36默認(rèn)的server.xml：
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<?xml version='1.0' encoding='utf-8'?> <!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --><!-- Note: A "Server" is not itself a "Container", so you may not define subcomponents such as "Valves" at this level. Documentation at /docs/config/server.html --><Server port="8005" shutdown="SHUTDOWN"> <!--APR library loader. Documentation at /docs/apr.html --> <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" /> <!--Initialize Jasper prior to webapps are loaded. Documentation at /docs/jasper-howto.html --> <Listener className="org.apache.catalina.core.JasperListener" /> <!-- Prevent memory leaks due to use of particular java/javax APIs--> <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" /> <!-- JMX Support for the Tomcat server. Documentation at /docs/non-existent.html --> <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" /> <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" /> <!-- Global JNDI resources Documentation at /docs/jndi-resources-howtohtml --> <GlobalNamingResources> <!-- Editable user database that can also be used by UserDatabaseRealm to authenticate users --> <Resource name="UserDatabase" auth="Container" type="org.apache.catalina.UserDatabase" description="User database that can be updated and saved" factory="org.apache.catalina.users.MemoryUserDatabaseFactory" pathname="conf/tomcat-users.xml" /> </GlobalNamingResources> <!-- A "Service" is a collection of one or more "Connectors" that share a single "Container" Note: A "Service" is not itself a "Container", so you may not define subcomponents such as "Valves" at this level. Documentation at /docs/config/service.html --> <Service name="Catalina"> <!--The connectors can use a shared executor, you can define one or more named thread pools--> <!-- <Executor name="tomcatThreadPool" namePrefix="catalina-exec-" maxThreads="150" minSpareThreads="4"/> --> <!-- A "Connector" represents an endpoint by which requests are received and responses are returned. Documentation at : Java HTTP Connector: /docs/config/http.html (blocking & non-blocking) Java AJP Connector: /docs/config/ajp.html APR (HTTP/AJP) Connector: /docs/apr.html Define a non-SSL HTTP/1 Connector on port 8080 --> <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> <!-- A "Connector" using the shared thread pool--> <!-- <Connector executor="tomcatThreadPool" port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> --> <!-- Define a SSL HTTP/1.1 Connector on port 8443 This connector uses the JSSE configuration, when using APR, the connector should be using the OpenSSL style configuration described in the APR documentation --> <!-- <Connector port="8443" protocol="HTTP/1" SSLEnabled="true" maxThreads="150" scheme="https" secure="true" clientAuth="false" sslProtocol="TLS" /> --> <!-- Define an AJP 1.3 Connector on port 8009 --> <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" /> <!-- An Engine represents the entry point (within Catalina) that processes every request The Engine implementation for Tomcat stand alone analyzes the HTTP headers included with the request, and passes them on to the appropriate Host (virtual host). Documentation at /docs/config/engine.html --> <!-- You should set jvmRoute to support load-balancing via AJP ie : <Engine name="Catalina" defaultHost="localhost" jvmRoute="jvm1"> --> <Engine name="Catalina" defaultHost="localhost"> <!--For clustering, please take a look at documentation at: /docs/cluster-howto.html (simple how to) /docs/config/cluster.html (reference documentation) --> <!-- <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/> --> <!-- The request dumper valve dumps useful debugging information about the request and response data received and sent by Tomcat. Documentation at: /docs/config/valve.html --> <!-- <Valve className="org.apache.catalina.valves.RequestDumperValve"/> --> <!-- This Realm uses the UserDatabase configured in the global JNDI resources under the key "UserDatabase". Any edits that are performed against this UserDatabase are immediately available for use by the Realm. --> <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase"/> <!-- Define the default virtual host Note: XML Schema validation will not work with Xerces 2.2. --> <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true" xmlValidation="false" xmlNamespaceAware="false"> <!-- SingleSignOn valve, share authentication between web applications Documentation at: /docs/config/valve.html --> <!-- <Valve className="org.apache.catalina.authenticator.SingleSignOn" /> --> <!-- Access log processes all example. Documentation at: /docs/config/valve.html --> <!-- <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs" prefix="localhost_access_log." suffix=".txt" pattern="common" resolveHosts="false"/> --> </Host> </Engine> </Service> </Server> |
