netty 支持多种通讯协议

通讯协议，指的是把Netty通讯管道中的二进制流转换为对象、把对象转换成二进制流的过程。转换过程追根究底还是ChannelInboundHandler、ChannelOutboundHandler的实现类在进行处理。ChannelInboundHandler负责把二进制流转换为对象，ChannelOutboundHandler负责把对象转换为二进制流。

接下来要构建一个Server，同时支持Person通讯协议和String通讯协议。

Person通讯协议：二进制流与Person对象间的互相转换。
String通讯协议：二进制流与有固定格式要求的String的相互转换。String格式表示的也是一个Person对象，格式规定为：name:xx;age:xx;sex:xx;

这时候，来自客户端的请求，会依次传递给两个通讯解析接口进行解析，每个通讯接口判断是否是匹配的协议，如果是则进行解析，如果不是则传递给其它通讯接口进行解析。

实体类：Person

package com.guowl.testobjcoder;
import java.io.Serializable;
public class Person implements Serializable{
private static final long serialVersionUID = 1L;
private String name;
private String sex;
private int age;
public String toString() {
return "name:" + name + " sex:" + sex + " age:" + age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}

Server端的类为：Server PersonDecoder StringDecoder BusinessHandler

1、Server 开启Netty服务

package com.guowl.testobjcoder;
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;
// 测试coder 和 handler 的混合使用
public class Server {
public void start(int port) throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new PersonDecoder());
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new BusinessHandler());
}
}).option(ChannelOption.SO_BACKLOG, 128).childOption(ChannelOption.SO_KEEPALIVE, true);
ChannelFuture f = b.bind(port).sync();
f.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
Server server = new Server();
server.start(8000);
}
}

2、PersonDecoder 把二进制流转换成Person对象

package com.guowl.testobjcoder;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import java.util.List;
import com.guowl.utils.ByteBufToBytes;
import com.guowl.utils.ByteObjConverter;
public class PersonDecoder extends ByteToMessageDecoder {
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
byte n = "n".getBytes()[0];
byte p = in.readByte();
in.resetReaderIndex();
if (n != p) {
// 把读取的起始位置重置
ByteBufToBytes reader = new ByteBufToBytes();
out.add(ByteObjConverter.byteToObject(reader.read(in)));
} else {
// 执行其它的decode
ctx.fireChannelRead(in);
}
}
}

3、StringDecoder 把满足条件的字符串转换成Person对象

package com.guowl.testobjcoder;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import java.util.List;
import com.guowl.utils.ByteBufToBytes;
public class StringDecoder extends ByteToMessageDecoder {
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
// 判断是否是String协议
byte n = "n".getBytes()[0];
byte p = in.readByte();
// 把读取的起始位置重置
in.resetReaderIndex();
if (n == p) {
ByteBufToBytes reader = new ByteBufToBytes();
String msg = new String(reader.read(in));
Person person = buildPerson(msg);
out.add(person);
//in.release();
} else {
ctx.fireChannelRead(in);
}
}
private Person buildPerson(String msg) {
Person person = new Person();
String[] msgArray = msg.split(";|:");
person.setName(msgArray[1]);
person.setAge(Integer.parseInt(msgArray[3]));
person.setSex(msgArray[5]);
return person;
}
}

4、BusinessHandler 展现客户端请求的内容

package com.guowl.testobjcoder;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class BusinessHandler extends ChannelInboundHandlerAdapter {
private Logger logger = LoggerFactory.getLogger(BusinessHandler.class);
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
Person person = (Person) msg;
logger.info("BusinessHandler read msg from client :" + person);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
ctx.flush();
}

<span style="white-space:pre"> </span>// 解决注意事项1中的问题。

<pre name="code" class="java"><span style="white-space:pre"> </span>@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
ctx.close();
}

}

客户端1发送Person格式的协议：Client ClientInitHandler PersonEncoder

1、Client

package com.guowl.testobjcoder;
import io.netty.bootstrap.Bootstrap;
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.NioSocketChannel;
public class Client {
public void connect(String host, int port) throws Exception {
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(workerGroup);
b.channel(NioSocketChannel.class);
b.option(ChannelOption.SO_KEEPALIVE, true);
b.handler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new PersonEncoder());
Person person = new Person();
person.setName("guowl");
person.setSex("man");
person.setAge(30);
ch.pipeline().addLast(new ClientInitHandler(person));
}
});
ChannelFuture f = b.connect(host, port).sync();
f.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
Client client = new Client();
client.connect("127.0.0.1", 8000);
}
}

2、ClientInitHandler 向服务端发送Person对象

package com.guowl.testobjcoder;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class ClientInitHandler extends ChannelInboundHandlerAdapter {
private static Logger logger = LoggerFactory.getLogger(ClientInitHandler.class);
private Person person;
public ClientInitHandler(Person person){
this.person = person;
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
logger.info("ClientInitHandler.channelActive");
ctx.write(person);
ctx.flush();
}
}

3、PersonEncoder 把Person对象转换成二进制进行传送

package com.guowl.testobjcoder;
import com.guowl.utils.ByteObjConverter;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;
public class PersonEncoder extends MessageToByteEncoder<Person> {
@Override
protected void encode(ChannelHandlerContext ctx, Person msg, ByteBuf out) throws Exception {
out.writeBytes(ByteObjConverter.objectToByte(msg));
}
}

客户端2发送String格式的协议：Client2 StringEncoder 同样使用了客户端1中定义的ClientInitHandler 进行数据发送操作。

1、Client2

package com.guowl.testobjcoder.client2;
import io.netty.bootstrap.Bootstrap;
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.NioSocketChannel;
import com.guowl.testobjcoder.ClientInitHandler;
import com.guowl.testobjcoder.Person;
public class Client2 {
public void connect(String host, int port) throws Exception {
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(workerGroup);
b.channel(NioSocketChannel.class);
b.option(ChannelOption.SO_KEEPALIVE, true);
b.handler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new StringEncoder());
Person person = new Person();
person.setName("guoxy");
person.setSex("girl");
person.setAge(4);
ch.pipeline().addLast(new ClientInitHandler(person));
}
});
ChannelFuture f = b.connect(host, port).sync();
f.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
Client2 client = new Client2();
client.connect("127.0.0.1", 8000);
}
}

2、StringEncoder 把Person对象转换成固定格式的String的二进制流进行传送

package com.guowl.testobjcoder.client2;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;
import com.guowl.testobjcoder.Person;
public class StringEncoder extends MessageToByteEncoder<Person> {
@Override
protected void encode(ChannelHandlerContext ctx, Person msg, ByteBuf out) throws Exception {
// 转成字符串：name:xx;age:xx;sex:xx;
StringBuffer sb = new StringBuffer();
sb.append("name:").append(msg.getName()).append(";");
sb.append("age:").append(msg.getAge()).append(";");
sb.append("sex:").append(msg.getSex()).append(";");
out.writeBytes(sb.toString().getBytes());
}
}

其它：工具类ByteBufToBytes（读取ByteBuf数据的工具类）、ByteObjConverter（Object与byte互转的工具类）在以前的文章中已经存在，在此省略。

注意事项：

1、该段代码能运行出结果，但是运行的时候会报 io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1 异常，已经解决。日志中的提示信息为：
An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception

说明缺少exceptionCaught方法，在server端最后一个Handler中增加这个方法即可。

2、PersonDecoder和StringDecoder中有一个if判断，是为了判断消息究竟是什么协议。如果是String协议的话，格式是【name:xx;age:xx;sex:xx;】，第一个字母是英文字母n，所以判断协议类型时候是读取二进制流的第一个字符进行判断，当然这种判断方式非常幼稚，以后有机会可以进行改善。

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netty 支持多种通讯协议

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