Tomcat源码解析系列二:Tomcat总体架构
Tomcat即是一个HTTP服务器,也是一个servlet容器,主要目的就是包装servlet,并对请求响应相应的servlet,纯servlet的web应用似乎很好理解Tomcat是如何装载servlet的,但,当使用一些MVC框架时,如spring MVC、strusts2,可能就找不出servlet在哪里?其实spring MVC框架就是一整个servlet,在web.xml中配置如下:
- <!-- Spring MVC servlet -->
- <servlet>
- <servlet-name>SpringMVC</servlet-name>
- <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
- <init-param>
- <param-name>contextConfigLocation</param-name>
- <param-value>classpath:spring-mvc.xml</param-value>
- </init-param>
- <load-on-startup>1</load-on-startup>
- <async-supported>true</async-supported>
- </servlet>
- <servlet-mapping>
- <servlet-name>SpringMVC</servlet-name>
- <!-- 此处可以可以配置成*.do,对应struts的后缀习惯 -->
- <url-pattern>/</url-pattern>
- </servlet-mapping>
- <span style="font-family:Comic Sans MS;font-size:18px;"><filter>
- <filter-name>struts2</filter-name>
- <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
- </filter>
- <filter-mapping>
- <filter-name>struts2</filter-name>
- <url-pattern>/*</url-pattern>
- </filter-mapping></span>
他的总体结构用下图来表示。
通过上图我们可以看出Tomcat中主要涉及Server,Service,Engine,Connector,Host,Context组件,之前用过Tomcat的童鞋是不是觉得这些组件的名称有点似曾相识的赶脚,没赶脚?!您再想想。好吧,不用你想了,我来告诉你吧。其实在Tomcat二进制分发包解压后,在conf目录中有一个server.xml文件,你打开它瞄两眼看看,是不是发现server.xml文件中已经包含了上述的几个名称。
- <?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">
- <!-- Security listener. Documentation at /docs/config/listeners.html
- <Listener className="org.apache.catalina.security.SecurityListener" />
- -->
- <!--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" />
- <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
- <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" />
- <!-- Global JNDI resources
- Documentation at /docs/jndi-resources-howto.html
- -->
- <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/1.1 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/1.1" 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="192.168.1.50" jvmRoute="jvm1">
- -->
- <Engine name="Catalina" defaultHost="192.168.1.50">
- <!--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"/>
- -->
- <!-- Use the LockOutRealm to prevent attempts to guess user passwords
- via a brute-force attack -->
- <Realm className="org.apache.catalina.realm.LockOutRealm">
- <!-- 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"/>
- </Realm>
- <Host name="192.168.1.50" appBase="webapps"
- unpackWARs="true" autoDeploy="true">
- <!-- 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
- Note: The pattern used is equivalent to using pattern="common" -->
- <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
- prefix="192.168.1.50_access_log." suffix=".txt"
- pattern="%h %l %u %t "%r" %s %b" />
- </Host>
- </Engine>
- </Service>
- </Server>
Tomcat加载时相应组件(容器)的配置参数都是从这个文件读进去的,这个文件也是Tomcat性能优化的关键。接下来我们就根据上图以及conf/server.xml的内容来一步步描述一下上面所说的各种组件吧。
Server
Server是Tomcat中最顶层的组件,它可以包含多个Service组件。在Tomcat源代码中Server组件对应源码中的 org.apache.catalina.core.StandardServer 类。StandardServer的继承关系图如下图所示:Lifecycle是Tomcat的生命周期接口。保持组件启动和停止一致的的机制通过实现org.apache.catalina.Lifecycle接口来实现。
Service
接下来咋们来看看Service组件,Service组件相当于Connetor和Engine组件的包装器,它将一个或者多个Connector组件和一个Engine建立关联。上述配置文件中,定义一个叫Catalina
的服务,并将Http,AJP(定向包的协议)这两个Connector关联到了一个名为Catalina
的Service,注意一个Connetor对应处理一种协议。Service组件对应Tomcat源代码中的org.apache.catalina.core.StandardService
,StandardService的继承关系图如下图所示:
Connector
既然Tomcat需要提供http服务,而我们知道http应用层协议最终都是需要通过TCP层的协议进行传递的,而Connector正是Tomcat中监听TCP网络连接的组件,一个Connector会监听一个独立的端口来处理来自客户端的连接。缺省的情况下Tomcat提供了如下两个Connector。我们分别描述一下:
- HTTP/1.1
<Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" />
上面定义了一个Connector,它缺省监听端口8080,这个端口我们可以根据具体情况进行改动。connectionTimeout
定义了连接超时时间,单位是毫秒,redirectPort
定义了ssl的重定向接口,根据缺省的配置,Connector会将ssl请求重定向到8443端口。 - AJP/1.3
AJP表示Apache Jserv Protocol
,此连接器将处理Tomcat和Aapache http服务器之间的交互,这个连接器是用来处理我们将Tomcat和Apache http服务器结合使用的情况。假如在同样的一台物理Server上面部署了一台Apache http服务器和多台Tomcat服务器,通过Apache服务器来处理静态资源以及负载均衡的时候,针对不同的Tomcat实例需要AJP监听不同的端口。
org.apache.catalina.connector.Connector
,它的继承关系图如下所示:
Engine
Tomcat中有一个容器的概念,而Engine,Host,Context都属于Contanier,我们先来说说最顶层的容器Engine.
一个Engine可以包含一个或者多个Host,也就是说我们一个Tomcat的实例可以配置多个虚拟主机。
缺省的情况下<Engine name="Catalina" defaultHost="localhost">
定义了一个名称为Cataline的Engine.Engine对应源代码中的org.apache.catalina.core.StandardEngine
,它的继承关系图如下图所示:
Host定义了一个虚拟主机,一个虚拟主机可以有多个Context,缺省的配置如下:<Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true">….</Host>
其中appBase
为webapps,也就是<CATALINA_HOME>\webapps
目录,unpackingWARS
属性指定在appBase指定的目录中的war包都自动的解压,缺省配置为true,autoDeploy
属性指定是否对加入到appBase目录的war包进行自动的部署,缺省为true.
Host对应源代码中的org.apache.catalina.core.StandardHost
,它的继承关系图如下所示:
Context
在Tomcat中,每一个运行的webapp其实最终都是以Context的形成存在,每个Context都有一个根路径和请求URL路径,Context对应源代码中的org.apache.catalina.core.StandardContext
,它的继承关系图如下图所示:
在Tomcat中我们通常采用如下的两种方式创建一个Context.下面分别描述一下:
- 在
<CATALINA-HOME>\webapps
目录中创建一个目录,这个时候将自动创建一个context,默认context的访问url为http://host:port/dirname
,你也可以通过在ContextRoot\META-INF
中创建一个context.xml的文件,其中包含如下的内容来指定应用的访问路径。<Context path="/yourUrlPath" />
- conf\server.xml文件中增加context元素。 第二种创建context的方法,我们可以选择在server.xml文件的
<Host>
元素,比如我们在server.xml文件中增加如下内容:
- .......
- <span style="line-height: 1.5;"> </span><span style="line-height: 1.5;">.........</span>
- <Context path="/mypath" docBase="/Users/xxx" reloadable="true">
- </Context>
- </Host>
- t;/Engine>
- </Service>
- t;/Server>
http://host:port/mypath
访问上面配置的context了。Valve
Valve中文意思是阀门,Valve是Tomcat中责任链模式的实现,通过链接多个Valve对请求进行处理。每个容器都有一个流水线Pipeline(过滤器链),每个流水线至少有一个阀门。其中Valve可以定义在任何的Container中,上面说的Engine,Host,Context都属于容器。tomcat 默认定义了一个名为org.apache.catalina.valves.AccessLogValve
的Valve,这个Valve负责拦截每个请求,然后记录一条访问日志。
通过上面的分析,我们发现Server,Service,Engine,Host,Context都实现了org.apache.catalina.Lifecycle
接口,通过这个接口管理了这些核心组件的生命周期,关于这些组件的生命周期,我们在下一篇文章描述。