import org.apache.mina.core.service.IoHandlerAdapter;
import org.apache.mina.core.session.IdleStatus;
import org.apache.mina.core.session.IoSession;public class ServerHandler extends IoHandlerAdapter{@Overridepublic void exceptionCaught(IoSession session, Throwable cause) throws Exception{System.out.println("报错啦............");cause.printStackTrace();}@Overridepublic void messageReceived( IoSession session, Object message ) throws Exception{String str = message.toString();System.out.println("messageReceived:"+str);session.write("hello world");}@Overridepublic void sessionIdle( IoSession session, IdleStatus status ) throws Exception{System.out.println( "IDLE " + session.getIdleCount( status ));}
}

IoFilter：过滤器层

这里我们做一个解码的编码的过滤层，这也是mina中最常用的。首先我们需要定义属于我们自己的协议，也就是数据包的格式：别以为这很复杂，其实很简单的。

我们知道数据都是字节类型的，那么我们的协议格式如下：前两位表示数据包的长度（一个short类型正好两个字节），第三位是闲置位，后面的是数据。长度是闲置位和

数据长度的和。这样我们就可以根据前两位确定，我们的数据包到那里结束。那么我们循环这么读，就会取得所有的数据包。是不是很简单啊，这个格式就是我们的协议。

为了更简单，这里我们客户端发往服务端的数据进行编码和解码，服务端发往客户端的就不编码了，客户端也就不用解码。服务端使用mina，客户端我们就使用基本的socket nio。

编码工厂类：

public class CodecFactory extends DemuxingProtocolCodecFactory{public CodecFactory(){super.addMessageEncoder(String.class, Encoder.class);super.addMessageDecoder(Decoder.class);}
}

解码类:

import java.util.ArrayList;
import java.util.List;import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.ProtocolDecoderOutput;
import org.apache.mina.filter.codec.demux.MessageDecoder;
import org.apache.mina.filter.codec.demux.MessageDecoderResult;
public class Decoder implements MessageDecoder {private byte[] r_curPkg = null;private int r_pos = -1; // 包计数器static private final int PKG_SIZE_BYTES = 2;//包长度public Decoder() { }@Overridepublic MessageDecoderResult decodable(IoSession session, IoBuffer in) {return MessageDecoderResult.OK;}@Overridepublic MessageDecoderResult decode(IoSession session, IoBuffer in,ProtocolDecoderOutput out) throws Exception {List<String> list = new ArrayList<String>();while (in.remaining() >= PKG_SIZE_BYTES || (r_pos >= 0 && in.hasRemaining())) {// 循环接收包,4为一个整型，表示包长度b, 如果上一个包未接收完成时，继续接收// 如果上个包已收完整，则创建新的包if (r_pos == -1) {//得到下一个包的长度,长度不包括前两位,即包的长度=压缩位长度+数据位长度int pkgLen = in.getShort(); //如果包长度小于0，那么此包错误，解码失败，返回。if (pkgLen < 0) {return MessageDecoderResult.NOT_OK;}in.get(); r_curPkg = new byte[pkgLen-1]; //数组长度为数据长度r_pos = 0;}int need = r_curPkg.length - r_pos; //需要读取的数据长度int length = in.remaining();//缓冲区中可读的数据长度if (length >= need) {// 可以把当前包读完整in.get(r_curPkg, r_pos, need); // 复制缓冲区中的数据到r_curPkg中// 处理接收到一个完整的包数据后，把包添加到池中，判断是否需要需要解压byte[] data = r_curPkg;String str = new String(data);list.add(str);r_curPkg = null;r_pos = -1;} else {// 如果剩下的字节数，不够一个包则int remainBytes = in.remaining();in.get(r_curPkg, r_pos, remainBytes);r_pos += remainBytes;return MessageDecoderResult.NEED_DATA;}}for (String protocol : list) {out.write(protocol);}return MessageDecoderResult.OK;}@Overridepublic void finishDecode(IoSession session, ProtocolDecoderOutput out) {}}

编码类：（没有进行编码，只进行了数据发送）

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.ProtocolEncoderOutput;
import org.apache.mina.filter.codec.demux.MessageEncoder;
public class Encoder implements MessageEncoder<String>{public Encoder(){}@Overridepublic void encode(IoSession session, String message, ProtocolEncoderOutput out)throws Exception {System.out.println("encode..................");String value = (String) message;  IoBuffer buf = IoBuffer.allocate(value.getBytes().length);  buf.setAutoExpand(true);  if (value != null){buf.put(value.trim().getBytes());  }  buf.flip();  out.write(buf); out.flush();}
}

IoService层：

import java.io.IOException;
import java.net.InetSocketAddress;import org.apache.mina.core.service.IoAcceptor;
import org.apache.mina.core.session.IdleStatus;
import org.apache.mina.filter.codec.ProtocolCodecFilter;
import org.apache.mina.filter.logging.LoggingFilter;
import org.apache.mina.transport.socket.nio.NioSocketAcceptor;public class MinaServer {private static final int PORT = 9123;public static void main(String [] args) throws IOException{IoAcceptor acceptor = new NioSocketAcceptor();acceptor.getFilterChain().addLast( "logger", new LoggingFilter() );acceptor.getFilterChain().addLast( "codec", new ProtocolCodecFilter(new CodecFactory()));acceptor.setHandler(new ServerHandler());acceptor.getSessionConfig().setReadBufferSize( 3 );acceptor.getSessionConfig().setIdleTime( IdleStatus.BOTH_IDLE, 10 );acceptor.bind( new InetSocketAddress(PORT) );}
}

到这里我们的服务端代码就写完了，

客户端实现

<span style="font-size:12px">public class SocketClient {public static void main(String...args)throws Exception{SocketChannel socketChannel = SocketChannel.open();socketChannel.connect(new InetSocketAddress("localhost",9123));byte [] bytes = "aaaa".getBytes();//对数据包进行编码ByteBuffer buffer = ByteBuffer.allocate(bytes.length+3);buffer.putShort((short)(bytes.length+1)); //包长度buffer.put((byte)1);//闲置位buffer.put(bytes);//数据buffer.flip();socketChannel.write(buffer);socketChannel.socket().shutdownOutput();String obj = receive(socketChannel);System.out.println(obj);}private static String receive(SocketChannel socketChannel)throws Exception{ByteBuffer buffer = ByteBuffer.allocate(1024);ByteArrayOutputStream baos = new ByteArrayOutputStream();int size = 0;byte [] bytes = null;while((size = socketChannel.read(buffer))>=0){buffer.flip();bytes = new byte[size];buffer.get(bytes);baos.write(bytes);buffer.clear();}bytes = baos.toByteArray();baos.close();return new String(bytes);}
}
</span>

所有的代码都写完了，先启动服务端的MinaServer，然后再启动客户端，我们就会看到结果。