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。