11.3 实现 

    WebSocket使用HTTP升级机制从一个普通的HTTP连接WebSocket，因为这个应用程序使用WebSocket总是开始于HTTP(s)，然后再升级。什么时候升级取决于应用程序本身。直接执行升级作为第一个操作一般是使用特定的url请求。

    在这里，如果url的结尾以/ws结束，我们将只会升级到WebSocket，否则服务器将发送一个网页给客户端。升级后的连接将通过WebSocket传输所有数据。逻辑图如下：

http://img.blog.csdn.net/20140731213833293?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvYWJjX2tleQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast

11.3.1 处理http请求 

    服务器将作为一种混合式以允许同时处理http和websocket，所以服务器还需要html页面，html用来充当客户端角色，连接服务器并交互消息。因此，如果客户端不发送/ws的uri，我们需要写一个ChannelInboundHandler用来处理FullHttpRequest。看下面代码：

[java] view plaincopy

  1. package netty.in.action;
  3. import io.netty.channel.ChannelFuture;
  4. import io.netty.channel.ChannelFutureListener;
  5. import io.netty.channel.ChannelHandlerContext;
  6. import io.netty.channel.DefaultFileRegion;
  7. import io.netty.channel.SimpleChannelInboundHandler;
  8. import io.netty.handler.codec.http.DefaultFullHttpResponse;
  9. import io.netty.handler.codec.http.DefaultHttpResponse;
  10. import io.netty.handler.codec.http.FullHttpRequest;
  11. import io.netty.handler.codec.http.FullHttpResponse;
  12. import io.netty.handler.codec.http.HttpHeaders;
  13. import io.netty.handler.codec.http.HttpResponse;
  14. import io.netty.handler.codec.http.HttpResponseStatus;
  15. import io.netty.handler.codec.http.HttpVersion;
  16. import io.netty.handler.codec.http.LastHttpContent;
  17. import io.netty.handler.ssl.SslHandler;
  18. import io.netty.handler.stream.ChunkedNioFile;
  20. import java.io.RandomAccessFile;
  22. /**
    • WebSocket，处理http请求
    • @author c.k
  27. */
  28. public class HttpRequestHandler extends
  29. SimpleChannelInboundHandler<FullHttpRequest> {
  30. //websocket标识
  31. private final String wsUri;
  33. public HttpRequestHandler(String wsUri) {
  34. this.wsUri = wsUri;
  35. }
  37. @Override
  38. protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest msg)
  39. throws Exception {
  40. //如果是websocket请求，请求地址uri等于wsuri
  41. if (wsUri.equalsIgnoreCase(msg.getUri())) {
  42. //将消息转发到下一个ChannelHandler
  43. ctx.fireChannelRead(msg.retain());
  44. } else {//如果不是websocket请求
  45. if (HttpHeaders.is100ContinueExpected(msg)) {
  46. //如果HTTP请求头部包含Expect: 100-continue，
  47. //则响应请求
  48. FullHttpResponse response = new DefaultFullHttpResponse(
  49. HttpVersion.HTTP_1_1, HttpResponseStatus.CONTINUE);
  50. ctx.writeAndFlush(response);
  51. }
  52. //获取index.html的内容响应给客户端
  53. RandomAccessFile file = new RandomAccessFile(
  54. System.getProperty("user.dir") + "/index.html", "r");
  55. HttpResponse response = new DefaultHttpResponse(
  56. msg.getProtocolVersion(), HttpResponseStatus.OK);
  57. response.headers().set(HttpHeaders.Names.CONTENT_TYPE,
  58. "text/html; charset=UTF-8");
  59. boolean keepAlive = HttpHeaders.isKeepAlive(msg);
  60. //如果http请求保持活跃，设置http请求头部信息
  61. //并响应请求
  62. if (keepAlive) {
  63. response.headers().set(HttpHeaders.Names.CONTENT_LENGTH,
  64. file.length());
  65. response.headers().set(HttpHeaders.Names.CONNECTION,
  66. HttpHeaders.Values.KEEP_ALIVE);
  67. }
  68. ctx.write(response);
  69. //如果不是https请求，将index.html内容写入通道
  70. if (ctx.pipeline().get(SslHandler.class) == null) {
  71. ctx.write(new DefaultFileRegion(file.getChannel(), 0, file
  72. .length()));
  73. } else {
  74. ctx.write(new ChunkedNioFile(file.getChannel()));
  75. }
  76. //标识响应内容结束并刷新通道
  77. ChannelFuture future = ctx
  78. .writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);
  79. if (!keepAlive) {
  80. //如果http请求不活跃，关闭http连接
  81. future.addListener(ChannelFutureListener.CLOSE);
  82. }
  83. file.close();
  84. }
  85. }
  87. @Override
  88. public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
  89. throws Exception {
  90. cause.printStackTrace();
  91. ctx.close();
  92. }
  93. }

11.3.2 处理WebSocket框架 

    WebSocket支持6种不同框架，如下图：

http://img.blog.csdn.net/20140731215506204?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvYWJjX2tleQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast

我们的程序只需要使用下面4个框架：

  • CloseWebSocketFrame
  • PingWebSocketFrame
  • PongWebSocketFrame

  • TextWebSocketFrame

    我们只需要显示处理TextWebSocketFrame，其他的会自动由WebSocketServerProtocolHandler处理，看下面代码：

[java] view plaincopy

  1. package netty.in.action;
  3. import io.netty.channel.ChannelHandlerContext;
  4. import io.netty.channel.SimpleChannelInboundHandler;
  5. import io.netty.channel.group.ChannelGroup;
  6. import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
  7. import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
  9. /**
    • WebSocket，处理消息
    • @author c.k
  12. *
  13. */
  14. public class TextWebSocketFrameHandler extends
  15. SimpleChannelInboundHandler<TextWebSocketFrame> {
  16. private final ChannelGroup group;
  18. public TextWebSocketFrameHandler(ChannelGroup group) {
  19. this.group = group;
  20. }
  22. @Override
  23. public void userEventTriggered(ChannelHandlerContext ctx, Object evt)
  24. throws Exception {
  25. //如果WebSocket握手完成
  26. if (evt == WebSocketServerProtocolHandler.ServerHandshakeStateEvent.HANDSHAKE_COMPLETE) {
  27. //删除ChannelPipeline中的HttpRequestHandler
  28. ctx.pipeline().remove(HttpRequestHandler.class);
  29. //写一个消息到ChannelGroup
  30. group.writeAndFlush(new TextWebSocketFrame("Client " + ctx.channel()
    • " joined"));
  32. //将Channel添加到ChannelGroup
  33. group.add(ctx.channel());
  34. }else {
  35. super.userEventTriggered(ctx, evt);
  36. }
  37. }
  39. @Override
  40. protected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg)
  41. throws Exception {
  42. //将接收的消息通过ChannelGroup转发到所以已连接的客户端
  43. group.writeAndFlush(msg.retain());
  44. }
  45. }

11.3.3 初始化ChannelPipeline 

    看下面代码：

[java] view plaincopy

  1. package netty.in.action;
  3. import io.netty.channel.Channel;
  4. import io.netty.channel.ChannelInitializer;
  5. import io.netty.channel.ChannelPipeline;
  6. import io.netty.channel.group.ChannelGroup;
  7. import io.netty.handler.codec.http.HttpObjectAggregator;
  8. import io.netty.handler.codec.http.HttpServerCodec;
  9. import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
  10. import io.netty.handler.stream.ChunkedWriteHandler;
  12. /**
    • WebSocket,初始化ChannelHandler
    • @author c.k
  15. *
  16. */
  17. public class ChatServerInitializer extends ChannelInitializer<Channel> {
  18. private final ChannelGroup group;
  20. public ChatServerInitializer(ChannelGroup group){
  21. this.group = group;
  22. }
  24. @Override
  25. protected void initChannel(Channel ch) throws Exception {
  26. ChannelPipeline pipeline = ch.pipeline();
  27. //编解码http请求
  28. pipeline.addLast(new HttpServerCodec());
  29. //写文件内容
  30. pipeline.addLast(new ChunkedWriteHandler());
  31. //聚合解码HttpRequest/HttpContent/LastHttpContent到FullHttpRequest
  32. //保证接收的Http请求的完整性
  33. pipeline.addLast(new HttpObjectAggregator(64 * 1024));
  34. //处理FullHttpRequest
  35. pipeline.addLast(new HttpRequestHandler("/ws"));
  36. //处理其他的WebSocketFrame
  37. pipeline.addLast(new WebSocketServerProtocolHandler("/ws"));
  38. //处理TextWebSocketFrame
  39. pipeline.addLast(new TextWebSocketFrameHandler(group));
  40. }

  42. }

    WebSocketServerProtcolHandler不仅处理Ping/Pong/CloseWebSocketFrame，还和它自己握手并帮助升级WebSocket。这是执行完成握手和成功修改ChannelPipeline，并且添加需要的编码器/解码器和删除不需要的ChannelHandler。

    看下图：

http://img.blog.csdn.net/20140731215752609?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvYWJjX2tleQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast ChannelPipeline通过ChannelInitializer的initChannel(...)方法完成初始化，完成握手后就会更改事情。一旦这样做了，WebSocketServerProtocolHandler将取代HttpRequestDecoder、WebSocketFrameDecoder13和HttpResponseEncoder、WebSocketFrameEncoder13。另外也要删除所有不需要的ChannelHandler已获得最佳性能。这些都是HttpObjectAggregator和HttpRequestHandler。下图显示ChannelPipeline握手完成：

http://img.blog.csdn.net/20140731215818178?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvYWJjX2tleQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast

    我们甚至没注意到它，因为它是在底层执行的。以非常灵活的方式动态更新ChannelPipeline让单独的任务在不同的ChannelHandler中实现。

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