首先我们看看时序图(第一次画 可能在时序图规则上有些问题)

管道任务

public class SimpleWrapper implements Wrapper, Pipeline {

  // the servlet instance
  private Servlet instance = null;
  private String servletClass;
  private Loader loader;
  private String name;
  private SimplePipeline pipeline = new SimplePipeline(this);
  protected Container parent = null;
  ...
}
public class SimplePipeline implements Pipeline {

  public SimplePipeline(Container container) {
    setContainer(container);
  }

  // The basic Valve (if any) associated with this Pipeline.
  protected Valve basic = null;
  // The Container with which this Pipeline is associated.
  protected Container container = null;
  // the array of Valves
  protected Valve valves[] = new Valve[0];            //所有的阀
}

invokeNext是StandardPipelineValveContext类中的方法(StandardPipelineValveContext是管道的一个内部类,因此可以访问管道的所有成员)
 public void invokeNext(Request request, Response response)
      throws IOException, ServletException {
      int subscript = stage;
      stage = stage + 1;
      // Invoke the requested Valve for the current request thread
      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");
      }
    }
  } // end of inner class

ok?如水般流过。下面这行代码值得我们仔细看看

valves[subscript].invoke(request, response, this);

也可参阅拙作

public class HeaderLoggerValve implements Valve, Contained {

  protected Container container;

  public void invoke(Request request, Response response, ValveContext valveContext)
    throws IOException, ServletException {

    // Pass this request on to the next valve in our pipeline
    valveContext.invokeNext(request, response);

    System.out.println("Header Logger Valve");
    ServletRequest sreq = request.getRequest();
    if (sreq instanceof HttpServletRequest) {
      HttpServletRequest hreq = (HttpServletRequest) sreq;
      Enumeration<?> headerNames = hreq.getHeaderNames();
      while (headerNames.hasMoreElements()) {
        String headerName = headerNames.nextElement().toString();
        String headerValue = http://www.mamicode.com/hreq.getHeader(headerName);>


这行代码 valveContext.invokeNext(request, response); 看懂了吧
另一方面 大家应该能看出来,所有的阀都是逆向执行的,每次执行一个阀的时候,阀都会先传递给后面的阀,等到后面的执行完毕后,才执行自己的业务逻辑。
当通道里的处了最后一个基础阀外,都走了一遍的时候自然就执行如下代码
 basic.invoke(request, response, this);
 问题是basic是谁?
这个咱们等会再说。

Pipeline接口
我们在这里使用的是SimplePipeline,它实现了Pipeline的接口。
public interface Pipeline {
public Valve getBasic();
public void setBasic(Valve valve);
public void addValve(Valve valve);
public Valve[] getValves();
public void invoke(Request request, Response response)
throws IOException, ServletException;
public void removeValve(Valve valve);
}
Pipeline里面有个基础阀,是最后调用的,负责处理request对象鱼response对象。因而这里有getset方法
通道里面存放的是阀,所以剩下的方法就不用多说了吧。
另外tomcat4中,还存在一个StandardPipelineValveContext,上面已经说它是SimplePipeline的一个内部类。

Valve接口
public interface Valve {
public String getInfo();
public void invoke(Request request, Response response,ValveContext context) throws IOException, ServletException;
}


很清晰,不是吗?

Contained接口
public interface Contained {
public Container getContainer();
public void setContainer(Container container);
}


实现这个接口的类,至多与一个servlet容器相关联。

Wrapper接口
首先我们在文章开始的时候就说了,Wrapper包装的是一个最基础的servlet
这个接口里面有两个方法比较重要
public javax.servlet.Servlet allocate() throws javax.servlet.ServletException;
public void load() throws javax.servlet.ServletException;
allocate会分配一个已经初始化的servlet实例,
load会载入它。


Wrapper应用程序
类图如下:


SimpleLoader类
public class SimpleLoader implements Loader {

  public static final String WEB_ROOT =
    System.getProperty("user.dir") + File.separator  + "webroot";

  ClassLoader classLoader = null;
  Container container = null;

  public SimpleLoader() {
    try {
      URL[] urls = new URL[1];
      URLStreamHandler streamHandler = null;
      File classPath = new File(WEB_ROOT);
      String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;
      urls[0] = new URL(null, repository, streamHandler);
      classLoader = new URLClassLoader(urls);
    }
    catch (IOException e) {
      System.out.println(e.toString() );
    }
  }
}


构造函数会初始会类加载器,供SimpleWrapper使用

SimpleWrapper类
该类实现了 org.apache.catalina.Wrapper 接口并且实现了 allocate 方法和load 方法。
器构造函数如下
  public SimpleWrapper() {
    pipeline.setBasic(new SimpleWrapperValve());
  }
上文我们曾问过,basic从哪里来,从这里来!

SimpleWrapperValve类
通过pipeline.setBasic(new SimpleWrapperValve())我们知道SimpleWrapperValve类是一个基础阀,用来处理传递Servlet的参数,如下:
public void invoke(Request request, Response response, ValveContext valveContext)
    throws IOException, ServletException {

    SimpleWrapper wrapper = (SimpleWrapper) getContainer();
    ServletRequest sreq = request.getRequest();
    ServletResponse sres = response.getResponse();
    Servlet servlet = null;
    HttpServletRequest hreq = null;
    if (sreq instanceof HttpServletRequest)
      hreq = (HttpServletRequest) sreq;
    HttpServletResponse hres = null;
    if (sres instanceof HttpServletResponse)
      hres = (HttpServletResponse) sres;

    // Allocate a servlet instance to process this request
    try {
      servlet = wrapper.allocate();
      if (hres!=null && hreq!=null) {
        servlet.service(hreq, hres);
      }
      else {
        servlet.service(sreq, sres);
      }
    }
    catch (ServletException e) {
    }
  }


 应该没有什么问题。

ClientIPLoggerValve类
是用来显示客户端的ip地址的,代码从略,另外还有HeaderLoggerValve,用来显示http的请求头,代码从略。


Bootstrap1启动类
public final class Bootstrap1 {
  @SuppressWarnings("deprecation")
public static void main(String[] args) {

/* call by using http://localhost:8080/ModernServlet,
   but could be invoked by any name */

    HttpConnector connector = new HttpConnector();
    Wrapper wrapper = new SimpleWrapper();
    wrapper.setServletClass("ModernServlet");
   
    Loader loader = new SimpleLoader();
    
    Valve valve1 = new HeaderLoggerValve();
    Valve valve2 = new ClientIPLoggerValve();

    wrapper.setLoader(loader);
    ((Pipeline) wrapper).addValve(valve1);
    ((Pipeline) wrapper).addValve(valve2);

    connector.setContainer(wrapper);

    try {
      connector.initialize();
      connector.start();

      // make the application wait until we press a key.
      System.in.read();
    }
    catch (Exception e) {
      e.printStackTrace();
    }
  }
}


运行结果如下:

看到了,其实在部分里,不管你请求那个服务,返回的结果都一样,为什么?这个还用我来解释吗?


这一章东西比较多,关于context容器的使用,我们放在下一节中。
how tomcat works 五 servlet容器 上