Java determines whether the socket is connected

There is a method sendUrgentData in the socket class, which will send one byte of data to the output stream. As long as the SO_OOBINLINE attribute of the other party's Socket is not turned on, this byte will be automatically discarded ( In Java, an exception is thrown), and the SO_OOBINLINE attribute is turned off by default. Recommended: java video tutorial

Example:

public class Nksocket extends Thread{ 
public String ip=null;//连接服务器的IP 
public Integer port=null;//连接服务器的端口 
private Socket socket=null;//套节字对象 
private boolean close = false; // 关闭连接标志位，true表示关闭，false表示连接 
private Integer sotimeout=1*1*10;//超时时间，以毫秒为单位 
//------------------------------------------------------------------------------ 
public Nksocket(){ 
   init(); 
} 
public Nksocket(String ip,Integer port){ 
   setIp(ip); 
   setPort(port); 
   init(); 
} 
/**
* 初始化socket对象
*/ 
public void init(){ 
   try { 
    InetAddress address = InetAddress.getByName(getIp()); 
    socket = new Socket(address,getPort()); 
    socket.setKeepAlive(true);//开启保持活动状态的套接字 
    socket.setSoTimeout(sotimeout);//设置超时时间 
    close=!Send(socket,"2");//发送初始数据，发送成功则表示已经连接上，发送失败表示已经断开 
   }catch(UnknownHostException e) { 
    e.printStackTrace(); 
   }catch(IOException e){ 
    e.printStackTrace(); 
   } 
} 
/**
* 读数据线程
*/ 
public void run() { 
   while(true){ 
    //---------读数据--------------------------- 
    close = isServerClose(socket);//判断是否断开 
    if(!close){//没有断开，开始读数据 
     String readtext = ReadText(socket); 
     if(readtext!=null && readtext.trim().length()>0){ 
      System.out.println("读取数据："+readtext); 
     } 
    } 
    //---------创建连接------------------------- 
    while(close){//已经断开，重新建立连接 
     try{ 
      System.out.println("重新建立连接："+getIp()+":"+getPort()); 
      InetAddress address = InetAddress.getByName(getIp()); 
      socket = new Socket(address,getPort()); 
      socket.setKeepAlive(true); 
      socket.setSoTimeout(sotimeout); 
      close = !Send(socket,"2"); 
      System.out.println("建立连接成功："+getIp()+":"+getPort()); 
     }catch(Exception se){ 
      System.out.println("创建连接失败:"+getIp()+":"+getPort()); 
      close=true; 
     } 
    } 
   } 
} 
/**
* 发送数据，发送失败返回false,发送成功返回true
* @param csocket
* @param message
* @return
*/ 
public Boolean Send(Socket csocket,String message){ 
   try{ 
    PrintWriter out = new PrintWriter(socket.getOutputStream(), true); 
    out.println(message); 
    return true; 
   }catch(Exception se){ 
    se.printStackTrace(); 
    return false; 
   } 
} 
/**
* 读取数据，返回字符串类型
* @param csocket
* @return
*/ 
public String ReadText(Socket csocket){ 
   try{ 
    csocket.setSoTimeout(sotimeout); 
    InputStream input = csocket.getInputStream(); 
    BufferedReader in = new BufferedReader(new InputStreamReader(input)); 
    char[] sn = new char[1000]; 
    in.read(sn); 
    String sc = new String(sn); 
    return sc; 
   }catch(IOException se){ 
    return null; 
   } 
} 
/**
* 判断是否断开连接，断开返回true,没有返回false
* @param socket
* @return
*/ 
public Boolean isServerClose(Socket socket){ 
   try{ 
    socket.sendUrgentData(0xFF);//发送1个字节的紧急数据，默认情况下，服务器端没有开启紧急数据处理，不影响正常通信 
    return false; 
   }catch(Exception se){ 
    return true; 
   } 
} 
/**
* 测试
* @param ags
*/ 
public static void main(String[] ags){ 
   Nksocket nksocket = new Nksocket("127.0.0.1",8090); 
   nksocket.start(); 
} 
//------------------------------------------------------------------------------ 
public String getIp() { 
   return ip; 
} 
public void setIp(String ip) { 
   this.ip = ip; 
} 
public Integer getPort() { 
   return port; 
} 
public void setPort(Integer port) { 
   this.port = port; 
} 
}

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