apache mina第三发-自定义通信协议（下）

mrbear

　　在实际的网络通信中，阻塞是很可能发生的。那我们可以设想如果我们的一条消息被分成了两截，分两次发来，那么我们的解码器中的doDecode方法被先后调用两次，在前一次中不足以解码出一条完整的信息，而在后一次调用中我们也不知道前面一次解码到了哪一步。这个问题我们通过引入一个上下文的概念来解决。
　　在doDecode方法中有一个IoSession类型的参数，它很类似于Web中的Session，拥有一个Map，用键值对的形式来存储参数。一个IoSession可以类比为阻塞IO中的一个连接，我们可以把解码过程中用到的所有变量都存在里面。为了程序的结构良好，我们把所有变量包装成一个Context对象，变量的初始化都放在Context的构造函数里，原来对变量的操作也就成了对Context的操作。改造后的解码器类如下所示

package mina.common;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.AttributeKey;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.CumulativeProtocolDecoder;
import org.apache.mina.filter.codec.ProtocolDecoderOutput;
/**
* 解码器类
* @author 尹定宇
* @Email 768166775@qq.com
* @version 2013-5-2 上午10:10:03
* @info
*/
public class CmccSipcDecoder extends CumulativeProtocolDecoder {
//字符集
private final Charset charset;
//上下文的key
private final AttributeKey CONTEXT = new AttributeKey(getClass(),"context");
//构造方法
public CmccSipcDecoder(Charset charset) {
this.charset = charset;
}

@Override
protected boolean doDecode(IoSession session, IoBuffer in,
ProtocolDecoderOutput out) throws Exception {
//得到上下文
Context ctx = getContext(session);
//设置缓冲区，初始长度为100，可以自动调整长度
IoBuffer buffer = ctx.getInnerBuffer();
//获得一个字符编码器
CharsetDecoder cd = charset.newDecoder();
//表示一行中第几个字节
int matchCount = ctx.getMatchCount();
//初始化几个字符串
String statusLine = ctx.getStatusLine(),
sender = ctx.getSender(),
receiver = ctx.getReceiver(),
length = ctx.getLength(),
sms = ctx.getSms();
//表示第几行
int line = ctx.getLine();
//从输入流中读取
while (in.hasRemaining()) {
byte b = in.get();
//游标前移
matchCount++;
buffer.put(b);
//读到了换行符，而且不是第五行
if (b == 10 && line < 4) {
//如果是第一行，得到状态行字符串
if (line == 0) {
buffer.flip();
statusLine = buffer.getString(matchCount, cd);
statusLine = statusLine.substring(0,
statusLine.length() - 1);
matchCount = 0;
buffer.clear();
ctx.setStatusLine(statusLine);
}
//发送方
if (line == 1) {
buffer.flip();
sender = buffer.getString(matchCount, cd);
sender = sender.substring(0, sender.length() - 1);
matchCount = 0;
buffer.clear();
ctx.setSender(sender);
}
//接收方
if (line == 2) {
buffer.flip();
receiver = buffer.getString(matchCount, cd);
receiver = receiver.substring(0, receiver.length()-1);
matchCount = 0;
buffer.clear();
ctx.setReceiver(receiver);
}
//短信的长度
if (line == 3) {
buffer.flip();
length = buffer.getString(matchCount, cd);
length = length.substring(0, length.length() - 1);
matchCount = 0;
buffer.clear();
ctx.setLength(length);
}
//行数递增
line++;
} else if (line == 4) {//如果是第五行，则读取短信内容

//当读到的字节数等于上一行所定义的短信长度时
if (matchCount == Long.parseLong(length.split(": ")[1]))
{
buffer.flip();
sms = buffer.getString(matchCount, cd);
ctx.setSms(sms);
ctx.setMatchCount(matchCount);
ctx.setLine(line);
break;
}
}
ctx.setMatchCount(matchCount);
ctx.setLine(line);
}
if(ctx.getLine()==4&&Long.parseLong(ctx.getLength().split(":")[1])==ctx.getMatchCount()){
SmsObject smsObject = new SmsObject();
smsObject.setSender(sender.split(": ")[1]);
smsObject.setReceiver(receiver.split(": ")[1]);
smsObject.setMessage(sms);
out.write(smsObject);
ctx.reset();
return true;
}else{
return false;
}
}
private Context getContext(IoSession session){
Context context = (Context)session.getAttribute(CONTEXT);
if(context == null){
context = new Context();
session.setAttribute(CONTEXT, context);
}
return context;
}
/**
* 存储上下文的内部类
* @author 尹定宇
* @Email 768166775@qq.com
* @version 2013-5-7 下午12:57:02
* @info
*/
private class Context{
private final IoBuffer innerBuffer;
private String statusLine = "";
private String sender = "";
private String receiver = "";
private String length = "";
private String sms = "";
public Context(){
innerBuffer = IoBuffer.allocate(100).setAutoExpand(true);
}
private int matchCount = 0;
private int line = 0;
public String getStatusLine() {
return statusLine;
}
public void setStatusLine(String statusLine) {
this.statusLine = statusLine;
}
public String getSender() {
return sender;
}
public void setSender(String sender) {
this.sender = sender;
}
public String getReceiver() {
return receiver;
}
public void setReceiver(String receiver) {
this.receiver = receiver;
}
public String getLength() {
return length;
}
public void setLength(String length) {
this.length = length;
}
public String getSms() {
return sms;
}
public void setSms(String sms) {
this.sms = sms;
}
public int getMatchCount() {
return matchCount;
}
public void setMatchCount(int matchCount) {
this.matchCount = matchCount;
}
public int getLine() {
return line;
}
public void setLine(int line) {
this.line = line;
}

public void reset(){
this.innerBuffer.clear();
this.matchCount = 0;
this.line = 0;
this.statusLine = "";
this.sender = "";
this.receiver = "";
this.length = "";
this.sms = "";
}
public IoBuffer getInnerBuffer() {
return innerBuffer;
}
}
}

　　有一点特别需要我们注意，就是所有变量都来自Context的get方法，基本类型的变量改变之后别忘了把它们set回去，当然如果你把变量完全隐藏起来，只把外界可能用到的操作对外提供接口，那就更好了。