服务器没有意识到客户端在Netty 4.x中发送的消息

Question

我尝试通过简单地实现以下示例来学习Netty 4.x。我有服务器和客户端。在某个时间点，客户端想知道当前日期时间，他会问服务器"现在几点了？当服务器意识到问题时，他将使用当前日期时间进行回复。

我的实现如下

TimeClientInboundHandler.java

public class TimeClientInboundHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ByteBuf byteBuf = (ByteBuf) msg;
try {
long currentTimeMillis = (byteBuf.readUnsignedInt() - 2208988800L) * 1000L;
System.out.println(new Date(currentTimeMillis));
ctx.close();
} finally {
byteBuf.release();
}
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
ctx.write("What time is it?");
ctx.flush();
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}

TimeServerInboundHandler.java

public class TimeServerInboundHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ByteBuf byteBuf = (ByteBuf) msg;
try {
byteBuf.readCharSequence(1024, StandardCharsets.UTF_8);
System.out.println(byteBuf.toString());
} finally {
((ByteBuf) msg).release();
}
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
final ByteBuf byteBuf = ctx.alloc().buffer(4);
byteBuf.writeInt((int) (System.currentTimeMillis() / 1000L + 2208988800L));
final ChannelFuture f = ctx.writeAndFlush(byteBuf);
f.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
assert f == future;
ctx.close();
}
});
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}

但是，我没有得到预期的结果。具体来说，在服务器端，问题"现在几点了？"还没有在控制台上打印出来。

我做错了什么？

Answer 1

原因

此问题有两个原因。

服务器端无法实现从客户端发送的消息，因为消息是以错误的方式写入的(从客户端(。与其ctx.write("What time is it?");，不如

实现如下ctx.write(Unpooled.coppiedBuffer("What time is it?", StandardCharsets.UTF_8);

此外，在TimeServerInboundHandler.java中，我们应该删除方法channelActive()。这是因为channelRead()永远不会被触发，但当然channelActive()通道处于活动状态时触发。

溶液

TimeClientInboundHandler.java

public class TimeClientInboundHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
ByteBuf byteBuf = (ByteBuf) msg;
try {
System.out.println("Client received: " + byteBuf.toString(StandardCharsets.UTF_8));
ctx.close();
} finally {
byteBuf.release();
}
}
@Override
public void channelActive(ChannelHandlerContext ctx) {
ctx.writeAndFlush(Unpooled.copiedBuffer("What time is it?", StandardCharsets.UTF_8));
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}

TimeServerInboundHandler.java

public class TimeServerInboundHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
ByteBuf byteBuf = (ByteBuf) msg;
try {
System.out.println("Server received: " + byteBuf.toString(StandardCharsets.UTF_8));
String answer = Utils.getCurrentTime();
ctx.writeAndFlush(Unpooled.copiedBuffer(answer, StandardCharsets.UTF_8));
} finally {
((ByteBuf) msg).release();
}
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) {
ctx.writeAndFlush(Unpooled.EMPTY_BUFFER)
.addListener(ChannelFutureListener.CLOSE);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}

Utils.java

public class Utils {
public static String getCurrentTime() {
long currentTimeMillis = ((System.currentTimeMillis() / 1000L + 2208988800L) - 2208988800L) * 1000L;
return new Date(currentTimeMillis).toString();
}
}