Hessian源码分析（二）------ HessianProxy

Hessian在客户端一块采用Proxy模式，当客户端调用远程接口时，HessianProxy会代理这个动作，在invoke方法中，把客户端请求的方法和参数序列化为预订格式的输出流，主要流程如下图所示：

下面我将详细解析一下invoke源码:

public Object invoke(Object proxy, Method method, Object []args)
    throws Throwable
  {
    String mangleName;
    synchronized (_mangleMap) {
      mangleName = _mangleMap.get(method);
    }
    if (mangleName == null) {
      String methodName = method.getName();
      Class []params = method.getParameterTypes();
      // equals and hashCode are special cased
      if (methodName.equals("equals")
	  && params.length == 1 && params[0].equals(Object.class)) {
	Object value = args[0];
	if (value == null || ! Proxy.isProxyClass(value.getClass()))
	  return new Boolean(false);
	HessianProxy handler = (HessianProxy) Proxy.getInvocationHandler(value);
	return new Boolean(_url.equals(handler.getURL()));
      }
      else if (methodName.equals("hashCode") && params.length == 0)
	return new Integer(_url.hashCode());
      else if (methodName.equals("getHessianType"))
	return proxy.getClass().getInterfaces()[0].getName();
      else if (methodName.equals("getHessianURL"))
	return _url.toString();
      else if (methodName.equals("toString") && params.length == 0)
	return "HessianProxy[" + _url + "]";
      
      if (! _factory.isOverloadEnabled())
	mangleName = method.getName();
      else
        mangleName = mangleName(method);
      synchronized (_mangleMap) {
	_mangleMap.put(method, mangleName);
      }
    }
    ......
}

这是invoke的开头，主要干的事情是把methodName缓存起来和过滤一些特殊调用，java反射是个比较耗性能的操作，把methodName缓存起来可以避免每次调用都要从method里得到methodName。另外，对equals、hashCode、getHessianType、getHessianURL等特殊方法的远程调用，HessianProxy不会走远程调用，而是直接返回。

接着往下看：

public Object invoke(Object proxy, Method method, Object []args)
    throws Throwable
  {
    ......
    InputStream is = null;
    URLConnection conn = null;
    HttpURLConnection httpConn = null;
    
    try {
           
      conn = sendRequest(mangleName, args);
     ......
    } catch (HessianProtocolException e) {
      throw new HessianRuntimeException(e);
    } finally {
     ......
     }
  }

这段主要是把方法名和参数序列化为网络输出流，并做网络请求，具体逻辑包装在sendRequest方法中：

protected URLConnection sendRequest(String methodName, Object []args)
    throws IOException
  {
    URLConnection conn = null;
    
    conn = _factory.openConnection(_url);
    boolean isValid = false;
    try {
      // Used chunked mode when available, i.e. JDK 1.5.
      if (_factory.isChunkedPost() && conn instanceof HttpURLConnection) {
	try {
	  HttpURLConnection httpConn = (HttpURLConnection) conn;
	  httpConn.setChunkedStreamingMode(8 * 1024);
	} catch (Throwable e) {
	}
      }
    
      addRequestHeaders(conn);
      OutputStream os = null;
      try {
	os = conn.getOutputStream();
      } catch (Exception e) {
	throw new HessianRuntimeException(e);
      }
      if (log.isLoggable(Level.FINEST)) {
	PrintWriter dbg = new PrintWriter(new LogWriter(log));
	os = new HessianDebugOutputStream(os, dbg);
      }
      
      AbstractHessianOutput out = _factory.getHessianOutput(os);
      out.call(methodName, args);
      out.flush();
      isValid = true;
      return conn;
    } finally {
      if (! isValid && conn instanceof HttpURLConnection)
	((HttpURLConnection) conn).disconnect();
    }
  }

sendRequest的主要流程是先初始化网络连接，然后用AbstractHessianOutput包装网络输出流，调用AbstractHessianOutput.call(methodName, args)完成网络输出，这个方法的细节会在hessian io的源码解析中详细分析。

下面接着看invoke方法：

public Object invoke(Object proxy, Method method, Object []args)
    throws Throwable
  {
      ......
      is = conn.getInputStream();
      AbstractHessianInput in = _factory.getHessianInput(is);
      in.startReply();
      Object value = in.readObject(method.getReturnType());
      if (value instanceof InputStream) {
	value = new ResultInputStream(httpConn, is, in, (InputStream) value);
	is = null;
	httpConn = null;
      }
      else
	in.completeReply();
      ......
  }

这一段主要是把输入流中取得返回值，具体是用AbstractHessianInput包装网络输入流，然后调用AbstractHessianInput.readObject从网络流中反序列化到实际返回值。