Pipeline和Value

Pipeline是管道，而Value就是管道中的阀门，Request和Response对象在管道中通过各个阀门的处理和控制。

每一个容器中都包含有管道

1	protected final Pipeline pipeline = new StandardPipeline(this);

且管道中都有一个必不可少的basic value，StandardContext对应的basic value为StandardContextValve，StandardEngine对应的basic value为StandardEngineValve，StandardHost对应的basic value为StandardHostValve，StandardWrapper对应的basic value为StandardWrapperValve

value存储

value是链式存储的，通过getNext、setNext来实现链式关系

public void addValve(Valve valve) {

    // 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);
}