5.2 管道任务

Container 的 invoke 方法的调用实际就是调用 Pipeline 的 invoke 方法，Pipeline 包含了容器要执行的任务，一个 valve 代表一个任务，BaseValve是容器的核心任务。阀类似过滤器，执行完成后会调用下一个阀，基础阀总是在最后执行。下面是本章 Pipeline 的实现

public class SimplePipeline implements Pipeline {
  // 构造函数
  public SimplePipeline(Container container) {
    setContainer(container);
  }
  // Pipeline 属性设置
  protected Valve basic = null;
  protected Container container = null;
  protected Valve valves[] = new Valve[0];
  // 成员变量的 getter 和 setter 方法
  ...
  public void setBasic(Valve valve) {
    this.basic = valve;
    ((Contained) valve).setContainer(container);
  }
  // 添加 Valve
  public void addValve(Valve valve) {
    if (valve instanceof Contained)
      ((Contained) valve).setContainer(this.container);
    synchronized (valves) {
      Valve results[] = new Valve[valves.length +1];
      System.arraycopy(valves, 0, results, 0, valves.length);
      results[valves.length] = valve;
      valves = results;
    }
  }
  // Container 调用 invoke 方法执行处理逻辑
  public void invoke(Request request, Response response) {
    // 调用第一个 Valve
    (new SimplePipelineValveContext()).invokeNext(request, response);
  }

  // 本章的 ValveContext 实现
  protected class SimplePipelineValveContext implements ValveContext {
    protected int stage = 0;
    // 遍历 Pipeline 的所有 Valve
    public void invokeNext(Request request, Response response) {
      int subscript = stage;
      stage = stage + 1;
      if (subscript < valves.length) {
        valves[subscript].invoke(request, response, this);
      }  else if ((subscript == valves.length) && (basic != null)) {
        basic.invoke(request, response, this);
      }  else { throw new ServletException("No valve");  }
    }
  } 
}