固定字符串的长度的方式主要是依赖于这个类，先看下jdk中的解释
A decoder that splits the received ByteBufs by the fixed number of bytes. For example, if you received the following four fragmented packets:
+---+----+------+----+ | A | BC | DEFG | HI | +---+----+------+----+A
FixedLengthFrameDecoder
(3) will decode them into the following three packets with the fixed length:
+-----+-----+-----+ | ABC | DEF | GHI | +-----+-----+-----+
翻译过来就是：
这个类是一个将接收的byteebuf缓冲对象按照固定的字节长度分割的解码器，例如，如果你收到的是以下片段，
+---+----+------+----+ | A | BC | DEFG | HI | +---+----+------+----+
一个按照固定3个字节拆分的解码器将会分割成：
+-----+-----+-----+ | ABC | DEF | GHI | +-----+-----+-----+
我们看下代码：
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
public class Server {
public static void main(String[] args) throws Exception{
//1 创建2个线程，一个是负责接收客户端的连接。一个是负责进行数据传输的
EventLoopGroup pGroup = new NioEventLoopGroup();
EventLoopGroup cGroup = new NioEventLoopGroup();
//2 创建服务器辅助类
ServerBootstrap b = new ServerBootstrap();
b.group(pGroup, cGroup)
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 1024)
.option(ChannelOption.SO_SNDBUF, 32*1024)
.option(ChannelOption.SO_RCVBUF, 32*1024)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel sc) throws Exception {
//设置定长字符串接收
sc.pipeline().addLast(new FixedLengthFrameDecoder(5));
//设置字符串形式的解码
sc.pipeline().addLast(new StringDecoder());
sc.pipeline().addLast(new ServerHandler());
}
});
//4 绑定连接
ChannelFuture cf = b.bind(8765).sync();
//等待服务器监听端口关闭
cf.channel().closeFuture().sync();
pGroup.shutdownGracefully();
cGroup.shutdownGracefully();
}
}ServerHandler
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
public class ServerHandler extends ChannelHandlerAdapter {
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
System.out.println(" server channel active... ");
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
String request = (String)msg;
System.out.println("Server :" + msg);
String response = request ;
ctx.writeAndFlush(Unpooled.copiedBuffer(response.getBytes()));
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable t) throws Exception {
}
}
Client
import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
public class Client {
public static void main(String[] args) throws Exception {
EventLoopGroup group = new NioEventLoopGroup();
Bootstrap b = new Bootstrap();
b.group(group)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel sc) throws Exception {
sc.pipeline().addLast(new FixedLengthFrameDecoder(5));
sc.pipeline().addLast(new StringDecoder());
sc.pipeline().addLast(new ClientHandler());
}
});
ChannelFuture cf = b.connect("127.0.0.1", 8765).sync();
cf.channel().writeAndFlush(Unpooled.wrappedBuffer("aaaaabbbbb".getBytes()));
cf.channel().writeAndFlush(Unpooled.copiedBuffer("ccccccc".getBytes()));
//等待客户端端口关闭
cf.channel().closeFuture().sync();
group.shutdownGracefully();
}
}
ClientHandler
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
public class ClientHandler extends ChannelHandlerAdapter{
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
System.out.println("client channel active... ");
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
String response = (String)msg;
System.out.println("Client: " + response);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
}
}
打印：
client
client channel active...
Client: aaaaa
Client: bbbbb
Client: cccccServer
server channel active...
Server :aaaaa
Server :bbbbb
Server :ccccc可以看到客户端发送aaaaabbbbb，被完美分割成aaaaa和bbbbb两部分，但ccccccc含有7个字符，服务器端只能收到ccccc
缺失了2个字符，这是因为使用定长字符串方式只会发送符合长度的字符串，多余的不会被发送，解决办法是可以补齐缺少的字s符，比如给多的cc补三个空格。这样server将会收到：
server channel active...
Server :aaaaa
Server :bbbbb
Server :ccccc
Server :cc