浅析Tomcat之StandardEngine

fablefe

Tomcat的容器中,有着4个层次的Servlet容器,这4个类型的容器一般情况下是从属的关系.其中顶层的容器为Engine.这个Engine是Tomcat的整个Servlet引擎.它的子容器是Host,默认情况下Tomcat会有一个Engine,它所对应的阀是StandardEngineValve
首先,我们可以回头看下server.xml的配置.

<Engine name="Catalina" defaultHost="localhost">  
<Realm className="org.apache.catalina.realm.LockOutRealm">  
<Realm className="org.apache.catalina.realm.UserDatabaseRealm"  
resourceName="UserDatabase"/>  
</Realm>  
<Host name="localhost"  appBase="webapps" unpackWARs="true" autoDeploy="true">  
<Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"  
prefix="localhost_access_log." suffix=".txt"  
pattern="%h %l %u %t "%r" %s %b" />  
</Host>  
</Engine>  
   从配置中可以知道Service节点除了定义Connector,还定义了Engine,它里面还有一个Host.也就是说StandardService初始化的时候,就构造了Servlet引擎StandardEngine等一系列的容器层次.我们就看看Engine的构造方法.

public StandardEngine() {  
super();  
pipeline.setBasic(new StandardEngineValve());  
/* Set the jmvRoute using the system property jvmRoute */  
try {  
setJvmRoute(System.getProperty("jvmRoute"));  
} catch(Exception ex) {  
log.warn(sm.getString("standardEngine.jvmRouteFail"));  
}  
// By default, the engine will hold the reloading thread  
backgroundProcessorDelay = 10;  
}
 StandardEngine继承自ContainerBase自然也就有了pipeline对象和invoke方法.构造函数中设置的基础阀是StandardEngineValve.它是Engine特有的.

public final void invoke(Request request, Response response)  
throws IOException, ServletException {  
// Select the Host to be used for this Request  
Host host = request.getHost();  
if (host == null) {  
response.sendError  
(HttpServletResponse.SC_BAD_REQUEST,  
sm.getString("standardEngine.noHost",  
request.getServerName()));  
return;  
}  
if (request.isAsyncSupported()) {  
request.setAsyncSupported(host.getPipeline().isAsyncSupported());  
}  
// Ask this Host to process this request  
host.getPipeline().getFirst().invoke(request, response);  
}
 上述代码是StandardEngineValve的invoke方法,从中我们可以知道它的作用只是把调用转发给了它的子容器Host,也就是他只起到了一个路由的作用.真正处理请求的还是在它的下级容器.
 
 
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