//Server.java 
importjava.io.*; 
importjava.net.*; 

publicclassServerextendsThread 
{ 
publicfinalstaticintDefault_Port=6543; 
protectdintport; 
protectdServerSockrtlisten_socket; 

//定义出错例程： 
如果出现异常错误，退出程序。 
Publicstaticvoidfail(Exceptione,Stringmsg) 
{ 
System.err.println(msg+":"+e); 
System.exit(1); 
} 

//定义并启动服务器的Socket例程， 
监听客户机的连接请求。 
publicServer(intport) 
{ 
if(port==0)port=Default_Port; 
this.port=port; 
try 
{ 
listen_socket=newServerSocket(port); 
} 
catch(IOExceptione)fail(e, 
"Exceptioncreatingserversocket"); 
System.out.println("Server: 
listeningonport"+port); 
This.start(); 
}

*/ 
publicvoidrun() 
{ 
try 
{ 
while(true) 
{ 
Socketclient_socket=listen_socket.accept(); 
Connectionc=newConnection(client_socket); 
} 
} 
catch(IOExceptione)fail 
(e,"Exceptionwhilelisteningforconnections") 
} 

//启动服务器主程序 
publicstaticvoidmain(Stringargs[]) 
{ 
intport=0; 
if(args.length==1) 
{ 
tryport=Integer.parseInt(args[0]); 
catch(NumberFormatExceptione)port=0; 
} 
newServer(port); 
}//Endofthemain 
}//EndofServerclass 

//以下定义了Connection类， 
它是用来处理与客户机的所有通信的线程。 
classConnectionextendsThread 
{ 
protectedSocketclient; 
protectedDataInputStreamin; 
protectedPrintStreamout; 

//初始化通信流并启动线程 
publicConnection(Socketclient_socket) 
{ 
client=client_socket; 
try 
{ 
in=newDataInputStream(client.getinputStream()); 
out=newPrintStream(client.getOutputStream()); 
} 
catch(IOExceptione) 
{ 
tryclient.close(); 
catch(IOExceptione2); 
System.err.println 
("Exceptionwhilegettingsocketstreram:"+e); 
Return; 
} 
this.start; 
}//EndofConnectionmethod 

//服务例程：读出一行文本； 
反转文本；返回文本。 
publicvoidrun() 
{ 
Stringline; 
StringBufferrevline; 
intlen; 

try 
{ 
for(;;) 
{ 
//Readaline 
line=in.readline(); 
if(line==null)break; 

//Reversetheline 
len=line.length(); 
revline=newStringBuffer(len); 
for(inti=len-1;i>=0;i--) 
revline.insert(len-1-I;line.charAt(i)); 

//Writeoutthereverseline 
out.println(revline); 
} 
catch(IOExceptione); 
finallytryclient.close(); 
catch(IOExceptione2); 
}//Endofrunmethod 
}//EndofConnectionclass

//Client.java 
importjava.io.*; 
importjava.net.*; 

publicclassClientextends 
{ 
publicstaticfinalintDefault_Port=6543; 

//定义出错例程 
publicstaticfinalvoidusage() 
{ 
System.out.println("Usage: 
JavaClient[]"); 
System.exit(0); 
} 

publicstaticvoidmain(Stringargs[]) 
{ 
intport=Default_Port; 
Sockets=null; 

//解析端口参数 
if((args.length!=1)&& 
(args.length!=2))usage(); 
if(args.length==1) 
port=Default_Port; 
else 
{ 
tryport=Integer.parseInt(args[1]); 
catch(NumberFormaatExceptione)usage(); 
} 

try{ 
//产生一个Socket， 
通过指定的端口与主机通信。 
s=newSocket(args[0],port); 

//产生用于发出和接收的文本字符流 
DataInputStreamsin=new 
DataInputStream(s.getInputStream()); 
PrintStreamsout=new 
DataInputStream(s.getInputStream()); 

//从控制台读入字符流 
DataInputStreamin=new 
DataInputStream(System.in); 

//返回连接的地址和端口 
System.out.println("Connected 
to"+s.getInetAddress() 
+":"+s.getPort()); 
Stringline; 

For(;;) 
{ 
//显示提示符 
System.out.print(">"); 
System.out.flush(); 

//读入控制台输入的一行字符 
line=in.readline(); 
if(line==null)break; 

//将接收的文本行送至服务器 
sout.println(line); 

//从服务器接收一行字符 
line=sin.readline(); 

//Checkifconnectionis 
closed(i.e.forEOF) 
if(line==null) 
{ 
System.out.println("Connectionclosedbyserver."); 
Break; 
} 

//在控制台上显示接收的字符 
System.out.println(line); 
}//Endofforloop 
}//Endoftry 

catch(IOExceptione)System.err.println(e); 

//Alwaysbesuretoclosethesocket 
finally 
{ 
tryif(s!=null)s.close(); 
catch(IOExceptione2); 
} 
}//Endofmain 
}//EndofClient