Java Socket 通信（同步阻塞式I/O）

java实现socket通信比较简单，因为它提供了ServerSocket 和Socket类。如下为一个简单的实例:TimeServer与TimeClient

1 TimeServer

public class TimeServer {

public static void main(String[] args) throws IOException {

int port = 8080;//server 端口采用8080
ServerSocket server = null;
Socket socket = null;
try {
server = new ServerSocket(port);
while(true){
socket = server.accept();
new Thread(new TimeHandler(socket)).start();
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if(server!=null){
server.close();
server =null;
System.out.println("the time server close...");
}
}
}

}

class TimeHandler implements Runnable{

private Socket socket;

public TimeHandler(){

}
public TimeHandler(Socket socket){
this();
this.socket = socket;
}

public void run() {
System.out.println(Thread.currentThread().getName()+" start success...");
BufferedReader in = null;
PrintWriter out = null;
try {
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream(),true);
while(true){
String str = in.readLine();
if("end".equals(str)){
break;
}
String time = str+":"+System.currentTimeMillis();
out.println(time);
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if(in!=null){
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
in = null;
}
if(out!=null){
out.close();
out= null;
}
if(socket!=null){
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
socket =null;
}
}

}
}

TimeServer对每一个Socket连接建立一个Handler处理线程，处理线程对inputstream流中的数据进行相应的处理后，将处理结果通过PrintWriter发送给客户端，在最后需要关闭输入流、输出流和socket套接字句柄资源。

2 TimeClient

public class TimeClient {

public static void main(String[] args) {
int port = 8080;
Socket socket = null;
BufferedReader in =null;
PrintWriter out =null;

try {
socket = new Socket("127.0.0.1", port);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream(),true);
out.println("hello");
out.println("world");
out.println("end");

System.out.println("send message success...");
while(true){
String res = in.readLine();
if("".equals(res)||res==null){
break;
}
System.out.println("the res is:"+res);
}

} catch (Exception e) {
e.printStackTrace();
}finally{
if(in!=null){
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
in = null;
}
if(out!=null){
out.close();
out= null;
}
if(socket!=null){
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
socket =null;
}
}

}

}

问题分析：同步阻塞式I/O的问题在于一个新的客户端请求接入时，服务端必须创建一个新的线程来处理接入的客户端，一个线程只能处理一个客户端，这种模型往往无法满足高性能、高并发的接入场景。

以上实例改编参考于《Netty权威指南（第2版）》