Hessian源码分析--HessianProxy

在上一篇博客 Hessian源码分析--HessianProxyFactory 中我们了解到，客户端获得的对象其实是HessianProxy生成的目标对象，当调用目标对象的方法时，会调用HessianProxy的invoke方法，如下，当调用HelloService的helloWorld函数时，会调用HessianProxy的invoke函数（对代理机制不懂的同学可以去学习一下）。

HessianProxyFactory factory = new HessianProxyFactory();
HelloService helloService = (HelloService) factory.create(HelloService.class, url);
System.out.println(helloService.helloWorld("world"));

接下来我们一步一步分析invoke函数，就会对Hessian的机制有一个比较清楚的了解：

invoke方法参数如下

 /**
   * Handles the object invocation.
   *
   * @param proxy 就是HessianProxy
   * @param method  调用的方法
   * @param args 方法需要的参数
   */
  public Object invoke(Object proxy, Method method, Object []args)
    throws Throwable

    String mangleName;

	//方法对象对应的名称缓存起来
    synchronized (_mangleMap) {
      mangleName = _mangleMap.get(method);
    }

    if (mangleName == null) {
	  //获得方法名称
      String methodName = method.getName();
	  //方法参数对象类型
      Class<?> []params = method.getParameterTypes();

      // equals and hashCode are special cased
	  //如果调用的方法是equals或者hashCode就特殊处理，不用远程调用
      if (methodName.equals("equals")
          && params.length == 1 && params[0].equals(Object.class)) {
        Object value = args[0];
        if (value == null || ! Proxy.isProxyClass(value.getClass()))
          return Boolean.FALSE;
        Object proxyHandler = Proxy.getInvocationHandler(value);
        if (! (proxyHandler instanceof HessianProxy))
          return Boolean.FALSE;
        HessianProxy handler = (HessianProxy) proxyHandler;
        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);

	   //保存函数对象对应的函数名称
      synchronized (_mangleMap) {
        _mangleMap.put(method, mangleName);
      }
    }

这部分操作是Hessian的关键，sendRequest就是向服务端发送请求，这期间还包括对参数值的序列化，发送请求之后，服务端会根据参数来调用服务端函数并将调用结果序列化之后返回，这样就可以通过conn.getInputStream来获得返回结果，

    InputStream is = null;
    HessianConnection conn = null;

    try {
      if (log.isLoggable(Level.FINER))
        log.finer("Hessian[" + _url + "] calling " + mangleName);

	  //向server发送请求，包括函数名及函数的参数
      conn = sendRequest(mangleName, args);
	  //获取请求调用之后的返回值
      is = getInputStream(conn);

      if (log.isLoggable(Level.FINEST)) {
        PrintWriter dbg = new PrintWriter(new LogWriter(log));
        HessianDebugInputStream dIs
          = new HessianDebugInputStream(is, dbg);

        dIs.startTop2();

        is = dIs;
      }

上面我们大体分析了一下sendRequest函数，接下来我们详细介绍一下这个函数的具体操作：

首先会根据URL来通过获得conn连接对象，接下来通过addRequestHeaders来设置一些默认的头部信息，

通过conn.getOutputStream()来获取OutputStream对象，根据OutputStream对象接下来获得Hessian提供的序列化对象out，

调用out.call(methodName, args)来序列化需要远程调用的函数名称和参数值，out.flush();将传递的数据刷新到outputStream中，

最后通过调用 conn.sendRequest();来发送请求，这个时候服务暴露端会得到这个请求（具体请求执行我们接下来分析）

并返回conn，此时调用结果值应该在conn的InputStream中了。

protected HessianConnection sendRequest(String methodName, Object []args)
    throws IOException
  {
    HessianConnection conn = null;
    //根据URL获取链接对象
    conn = _factory.getConnectionFactory().open(_url);
    boolean isValid = false;

    try {
	  //在请求中设置一些头的默认值
      addRequestHeaders(conn);

      OutputStream os = null;

      try {
		//获取OutputStream
        os = conn.getOutputStream();
      } catch (Exception e) {
        throw new HessianRuntimeException(e);
      }

      if (log.isLoggable(Level.FINEST)) {
        PrintWriter dbg = new PrintWriter(new LogWriter(log));
        HessianDebugOutputStream dOs = new HessianDebugOutputStream(os, dbg);
        dOs.startTop2();
        os = dOs;
      }

      AbstractHessianOutput out = _factory.getHessianOutput(os);
	  //对函数名和参数值进行二进制序列化
      out.call(methodName, args);
      out.flush();
      //向暴露的服务端发送请求
      conn.sendRequest();

      isValid = true;

      return conn;
    } finally {
      if (! isValid && conn != null)
        conn.destroy();
    }
  }

当服务暴露端返回值之后，接下来就是返回值的处理了，因为服务端给我们的也是二进制数据，所以我们需要感觉函数参数的类型来反序列化得到结果，上面我们已经分析到

is = getInputStream(conn)，这样返回值就在is中，首先第一个读到的是一个code，这样应该是一个标记值，接下来读到的就是主版本号和副版本号了，

in = _factory.getHessian2Input(is)是用来获得反序列化对象

Object value = in.readReply(method.getReturnType()) 这样就可以根据方法的返回类型来反序列化结果值了，这样整个的Hessian的客户端的实现机制就是这样了。

      AbstractHessianInput in;

      int code = is.read();

      if (code == 'H') {
        int major = is.read();
        int minor = is.read();

        in = _factory.getHessian2Input(is);

        Object value = in.readReply(method.getReturnType());

        return value;
      }
      else if (code == 'r') {
        int major = is.read();
        int minor = is.read();

        in = _factory.getHessianInput(is);

        in.startReplyBody();

        Object value = in.readObject(method.getReturnType());

        if (value instanceof InputStream) {
          value = new ResultInputStream(conn, is, in, (InputStream) value);
          is = null;
          conn = null;
        }
        else
          in.completeReply();

        return value;

接下来我们会对序列化和反序列化机制，已经连接请求机制也会简单分析。

HessianProxy的完整源码解析：

public class HessianProxy implements InvocationHandler, Serializable {
  private static final Logger log
    = Logger.getLogger(HessianProxy.class.getName());

  protected HessianProxyFactory _factory;

  private WeakHashMap<Method,String> _mangleMap
    = new WeakHashMap<Method,String>();

  private Class<?> _type;
  private URL _url;

  protected HessianProxy(URL url, HessianProxyFactory factory)
  {
    this(url, factory, null);
  }

  protected HessianProxy(URL url,
                         HessianProxyFactory factory,
                         Class<?> type)
  {
    _factory = factory;
    _url = url;
    _type = type;
  }

  public URL getURL()
  {
    return _url;
  }

  /**
   * Handles the object invocation.
   *
   * @param proxy 就是HessianProxy
   * @param method  调用的方法
   * @param args 方法需要的参数
   */
  public Object invoke(Object proxy, Method method, Object []args)
    throws Throwable
  {
    String mangleName;

	//方法对象对应的名称缓存起来
    synchronized (_mangleMap) {
      mangleName = _mangleMap.get(method);
    }

    if (mangleName == null) {
	  //获得方法名称
      String methodName = method.getName();
	  //方法参数对象类型
      Class<?> []params = method.getParameterTypes();

      // equals and hashCode are special cased
	  //如果调用的方法是equals或者hashCode就特殊处理，不用远程调用
      if (methodName.equals("equals")
          && params.length == 1 && params[0].equals(Object.class)) {
        Object value = args[0];
        if (value == null || ! Proxy.isProxyClass(value.getClass()))
          return Boolean.FALSE;
        Object proxyHandler = Proxy.getInvocationHandler(value);
        if (! (proxyHandler instanceof HessianProxy))
          return Boolean.FALSE;
        HessianProxy handler = (HessianProxy) proxyHandler;
        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);

	   //保存函数对象对应的函数名称
      synchronized (_mangleMap) {
        _mangleMap.put(method, mangleName);
      }
    }

    InputStream is = null;
    HessianConnection conn = null;

    try {
      if (log.isLoggable(Level.FINER))
        log.finer("Hessian[" + _url + "] calling " + mangleName);

	  //向server发送请求，包括函数名及函数的参数
      conn = sendRequest(mangleName, args);
	  //获取请求调用之后的返回值
      is = getInputStream(conn);

      if (log.isLoggable(Level.FINEST)) {
        PrintWriter dbg = new PrintWriter(new LogWriter(log));
        HessianDebugInputStream dIs
          = new HessianDebugInputStream(is, dbg);

        dIs.startTop2();

        is = dIs;
      }

      AbstractHessianInput in;
	  //获取返回码
      int code = is.read();

      if (code == 'H') {
        int major = is.read();
        int minor = is.read();
		//获得对象Hessian2Input
        in = _factory.getHessian2Input(is);
		//根据方法返回值类型，反序列化获得返回值
        Object value = in.readReply(method.getReturnType());

        return value;
      }
      else if (code == 'r') {
        int major = is.read();
        int minor = is.read();

        in = _factory.getHessianInput(is);

        in.startReplyBody();

        Object value = in.readObject(method.getReturnType());

        if (value instanceof InputStream) {
          value = new ResultInputStream(conn, is, in, (InputStream) value);
          is = null;
          conn = null;
        }
        else
          in.completeReply();
		//得到远程调用结果
        return value;
      }
      else
        throw new HessianProtocolException("'" + (char) code + "' is an unknown code");
    } catch (HessianProtocolException e) {
      throw new HessianRuntimeException(e);
    } finally {
      try {
        if (is != null)
          is.close();
      } catch (Exception e) {
        log.log(Level.FINE, e.toString(), e);
      }

      try {
        if (conn != null)
          conn.destroy();
      } catch (Exception e) {
        log.log(Level.FINE, e.toString(), e);
      }
    }
  }

  //获取HessianConnection中的返回值
  protected InputStream getInputStream(HessianConnection conn)
    throws IOException
  {
    InputStream is = conn.getInputStream();

    if ("deflate".equals(conn.getContentEncoding())) {
      is = new InflaterInputStream(is, new Inflater(true));
    }

    return is;
  }

  protected String mangleName(Method method)
  {
    Class<?> []param = method.getParameterTypes();

    if (param == null || param.length == 0)
      return method.getName();
    else
      return AbstractSkeleton.mangleName(method, false);
  }

  /**
   * Sends the HTTP request to the Hessian connection.
   */
  protected HessianConnection sendRequest(String methodName, Object []args)
    throws IOException
  {
    HessianConnection conn = null;
    //根据URL获取链接对象
    conn = _factory.getConnectionFactory().open(_url);
    boolean isValid = false;

    try {
	  //在请求中设置一些头的默认值
      addRequestHeaders(conn);

      OutputStream os = null;

      try {
		//获取OutputStream
        os = conn.getOutputStream();
      } catch (Exception e) {
        throw new HessianRuntimeException(e);
      }

      if (log.isLoggable(Level.FINEST)) {
        PrintWriter dbg = new PrintWriter(new LogWriter(log));
        HessianDebugOutputStream dOs = new HessianDebugOutputStream(os, dbg);
        dOs.startTop2();
        os = dOs;
      }

      AbstractHessianOutput out = _factory.getHessianOutput(os);
	  //对函数名和参数值进行二进制序列化
      out.call(methodName, args);
      out.flush();
      //向暴露的服务端发送请求
      conn.sendRequest();

      isValid = true;

      return conn;
    } finally {
      if (! isValid && conn != null)
        conn.destroy();
    }
  }

  //在请求中设置一些头的默认值
  protected void addRequestHeaders(HessianConnection conn)
  {
    conn.addHeader("Content-Type", "x-application/hessian");
    conn.addHeader("Accept-Encoding", "deflate");

    String basicAuth = _factory.getBasicAuth();

    if (basicAuth != null)
      conn.addHeader("Authorization", basicAuth);
  }

  /**
   * Method that allows subclasses to parse response headers such as cookies.
   * Default implementation is empty.
   * @param conn
   */
  protected void parseResponseHeaders(URLConnection conn)
  {
  }

  public Object writeReplace()
  {
    return new HessianRemote(_type.getName(), _url.toString());
  }

  static class ResultInputStream extends InputStream {
    private HessianConnection _conn;
    private InputStream _connIs;
    private AbstractHessianInput _in;
    private InputStream _hessianIs;

    ResultInputStream(HessianConnection conn,
                      InputStream is,
                      AbstractHessianInput in,
                      InputStream hessianIs)
    {
      _conn = conn;
      _connIs = is;
      _in = in;
      _hessianIs = hessianIs;
    }

    public int read()
      throws IOException
    {
      if (_hessianIs != null) {
        int value = _hessianIs.read();

        if (value < 0)
          close();

        return value;
      }
      else
        return -1;
    }

    public int read(byte []buffer, int offset, int length)
      throws IOException
    {
      if (_hessianIs != null) {
        int value = _hessianIs.read(buffer, offset, length);

        if (value < 0)
          close();

        return value;
      }
      else
        return -1;
    }

    public void close()
      throws IOException
    {
      HessianConnection conn = _conn;
      _conn = null;

      InputStream connIs = _connIs;
      _connIs = null;

      AbstractHessianInput in = _in;
      _in = null;

      InputStream hessianIs = _hessianIs;
      _hessianIs = null;

      try {
        if (hessianIs != null)
          hessianIs.close();
      } catch (Exception e) {
        log.log(Level.FINE, e.toString(), e);
      }

      try {
        if (in != null) {
          in.completeReply();
          in.close();
        }
      } catch (Exception e) {
        log.log(Level.FINE, e.toString(), e);
      }

      try {
        if (connIs != null) {
          connIs.close();
        }
      } catch (Exception e) {
        log.log(Level.FINE, e.toString(), e);
      }

      try {
        if (conn != null) {
          conn.close();
        }
      } catch (Exception e) {
        log.log(Level.FINE, e.toString(), e);
      }
    }
  }
  //日志相关
  static class LogWriter extends Writer {
    private Logger _log;
    private Level _level = Level.FINEST;
    private StringBuilder _sb = new StringBuilder();

    LogWriter(Logger log)
    {
      _log = log;
    }

    public void write(char ch)
    {
      if (ch == '\n' && _sb.length() > 0) {
        _log.fine(_sb.toString());
        _sb.setLength(0);
      }
      else
        _sb.append((char) ch);
    }

    public void write(char []buffer, int offset, int length)
    {
      for (int i = 0; i < length; i++) {
        char ch = buffer[offset + i];

        if (ch == '\n' && _sb.length() > 0) {
          _log.log(_level, _sb.toString());
          _sb.setLength(0);
        }
        else
          _sb.append((char) ch);
      }
    }

    public void flush()
    {
    }

    public void close()
    {
      if (_sb.length() > 0)
        _log.log(_level, _sb.toString());
    }
  }
}