tomcat 7 源码分析-13 处理request的Valve和Valve的链表Pipeline

sonyet

　　tomcat打开endpoint的监听对通过某种协议，通常下是http的信息进行解析，组装成request，接着给Http11Protocol（ProtocolHandler）和Http11Processor处理。

adapter.service(request, response);
 
connector.getService().getContainer().getPipeline().getFirst().invoke(request, response);
　　最终选择具体的Valve类处理request并生成response。
　　Valve和Pipeline的关系：Pipeline是valve的链表，表头是first，表尾是basic，具体的实现是StandardPipeline。
　　valve的实现是ValveBase及其子类。
　　先看ValveBase的定义

public abstract class ValveBase extends LifecycleMBeanBase
implements Contained, Valve {
//------------------------------------------------------ Constructor
public ValveBase() {
this(false);
}
public ValveBase(boolean asyncSupported) {
this.asyncSupported = asyncSupported;
}
........

/**
* The next Valve in the pipeline this Valve is a component of.
*/
protected Valve next = null;
　　next就如同C和C++数据结构描述的指针，形如

struct valve{
valve * next
};
　　StandardPipeline的具体实现

public class StandardPipeline extends LifecycleBase
implements Pipeline, Contained {
...............................
/**
* The basic Valve (if any) associated with this Pipeline.
*/
protected Valve basic = null;

/**
* The first valve associated with this Pipeline.
*/
protected Valve first = null;
　　StandardPipeline设置了两个哨兵，一个basic，一个是first。对链表的操作增加删除等，对哨兵有特殊处理的。
　　看个add的例子

    public void addValve(Valve valve) {
// Validate that we can add this Valve
if (valve instanceof Contained)
((Contained) valve).setContainer(this.container);
// Start the new component if necessary
if (getState().isAvailable()) {
if (valve instanceof Lifecycle) {
try {
((Lifecycle) valve).start();
} catch (LifecycleException e) {
log.error("StandardPipeline.addValve: start: ", e);
}
}
}
// Add this Valve to the set associated with this Pipeline
if (first == null) {
first = valve;
valve.setNext(basic);
} else {
Valve current = first;
while (current != null) {
if (current.getNext() == basic) {
current.setNext(valve);
valve.setNext(basic);
break;
}
current = current.getNext();
}
}
container.fireContainerEvent(Container.ADD_VALVE_EVENT, valve);
}
　　add一个元素是加在basic之前，处理pipeline的时候，是先取出first。
　　所以如果first==null，表面还没有pipeline种还没有元素，此时就先设置first。
　　不然，先找到basic以前的位置，将新的valve插入在basic之前，进行排队。
　　验证下可以看下面的remove操作

    public void removeValve(Valve valve) {
Valve current;
if(first == valve) {
first = first.getNext();
current = null;
} else {
current = first;
}
while (current != null) {
if (current.getNext() == valve) {
current.setNext(valve.getNext());
break;
}
current = current.getNext();
}
if (first == basic) first = null;
if (valve instanceof Contained)
((Contained) valve).setContainer(null);
// Stop this valve if necessary
if (getState().isAvailable()) {
if (valve instanceof Lifecycle) {
try {
((Lifecycle) valve).stop();
} catch (LifecycleException e) {
log.error("StandardPipeline.removeValve: stop: ", e);
}
}
}
try {
((Lifecycle) valve).destroy();
} catch (LifecycleException e) {
log.error("StandardPipeline.removeValve: destroy: ", e);
}
container.fireContainerEvent(Container.REMOVE_VALVE_EVENT, valve);
}