TextLineCodecFactory笔记

Mina的TextLineCodecFactory将字符串编码为字节流，将字节流解码为字符串，下面是使用中遇到的两个问题。 TextLineCodecFactory改变了message的类型
acceptor上挂了textCodec后handler的messageReceived方法中的session是String型（用"message.getClass().getName()"查看），

[INFO] [2012-04-05 16:18:54,317] [com.leechau.mina.echoServer.EchoProtocolHandler] - [Received : hi(java.lang.String)]

否则是IoBuffer：

[INFO] [2012-04-05 15:23:36,760] [com.leechau.mina.echoServer.EchoProtocolHandler] - [message type is: org.apache.mina.core.buffer.SimpleBufferAllocator$SimpleBuffer]

因此挂上TextLineCodecFactory后在handler的messageReceived方法中message参数可直接强转为String；

不能正确解码换行符问题及解决办法
连接Echo Server后有时会出现下面的现象：

hi{enter}

send:

hi

造成这一现象的原因是下面的配置方法使TextLineCodecFactory使用了默认的编解码行分隔符（encoder/decoder line delimeter），即用Unix LineDelimeter(/n)作为编码行分隔符，用AUTO LineDelimeter（\r或者\n，详见Mina API doc对LineDelimeter类的说明）作为解码行分隔符：

acceptor.getFilterChain().addLast("textCodec",new ProtocolCodecFilter(new TextLineCodecFactory(Charset.forName("UTF-8"))));

解决这一问题的办法是指定编解码行分隔符：

acceptor.getFilterChain().addLast("textCodec",

new ProtocolCodecFilter(new TextLineCodecFactory(Charset.forName("UTF-8"),

LineDelimiter.DEFAULT.getValue(), LineDelimiter.DEFAULT.getValue())));

效果如下：

hi{enter}
send:
hi

如果不希望每次session.write(msg)后编码器自动加上回车符，需要将编码行分隔符指定为NUL：

acceptor.getFilterChain().addLast(" textCodec",

new ProtocolCodecFilter(new TextLineCodecFactory(Charset.forName("UTF-8"),

LineDelimiter.NUL.getValue(), LineDelimiter.DEFAULT.getValue())));

效果如下：

hi{enter}
send: hi

源代码
Main.java

package com.leechau.mina.echoServer;
import java.net.InetSocketAddress;
import java.nio.charset.Charset;
import org.apache.mina.filter.codec.ProtocolCodecFilter;
import org.apache.mina.filter.codec.textline.TextLineCodecFactory;
import org.apache.mina.filter.logging.LoggingFilter;
import org.apache.mina.transport.socket.SocketAcceptor;
import org.apache.mina.transport.socket.nio.NioSocketAcceptor;
public class Main {
private static final int PORT = 8293;
public static void main(String[] args) throws Exception {
SocketAcceptor acceptor = new NioSocketAcceptor();
acceptor.getFilterChain().addLast("logger", new LoggingFilter());
acceptor.getFilterChain().addLast("textCodec",
new ProtocolCodecFilter(new TextLineCodecFactory(Charset.forName("UTF-8"),
LineDelimiter.NUL.getValue() , LineDelimiter.DEFAULT.getValue())));
acceptor.setHandler(new EchoProtocolHandler());
acceptor.bind(new InetSocketAddress(PORT));
System.out.println("Listening on port " + PORT);
}
}

EchoProtocolHandler.java

package com.leechau.mina.echoServer;
import org.apache.mina.core.service.IoHandlerAdapter;
import org.apache.mina.core.session.IoSession;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class EchoProtocolHandler extends IoHandlerAdapter {
private static final Logger LOGGER = LoggerFactory
.getLogger(EchoProtocolHandler.class);
@Override
public void messageReceived(IoSession session, Object message) throws Exception {
LOGGER.info("Received : " + message + "(" + message.getClass().getName() + ")");
session.write("send: ");
session.write(message);
}
}