Tcp是基于传输层的面向连接的可靠通讯协议，其优点是基于连接，使得服务端和客户端可以实现双向通信，且实时性高，在需要服务端主动向客户端推送数据的应用场景中，使用TCP协议是一种很好的方式。

初学Android，将Android中Tcp的使用方式记录一下，希望对新学Android开发的新同学有帮助，这里主要介绍TcpClient的使用，因为很少会用Android来建立TcpServer端。

这里主要介绍Tcp客户端的几个应用：

1.与服务器建立连接

2.向服务端发送数据

3.接收服务端返回的数据

4.断线重连机制

在Android中使用socket有两个地方需要注意的：

1.在AndroidMainfest.xml中需要添加对网络的权限支持

<uses-permission android:name="android.permission.INTERNET" />

2.Android中规定对socket的操作必须在线程中进行，如在主线程中进行操作会出现无法收发数据的情况。

（1）创建socket,与服务器建立连接

InetSocketAddress SerAddr = new InetSocketAddress(”192.168.1.100“,9988); //设置服务的IP地址和端口

try {        socket.connect(SerAddr,3000);   //尝试连接服务器    }catch (Exception e){

}
（2）发送数据

try { 　　　

　　/注意采用utf-8编码确保中文传输不会乱码

　　　　BufferedWriter bufferedWriter =new BufferedWriter(new OutputStreamWriter( socket.getOutputStream(),"utf-8")); 

  　　 bufferedWriter.write(”Hello“);   　　bufferedWriter.flush();

    }catch (Exception e){

}

　　　
（3）接收数据

try {

　　　　inputStream = new DataInputStream(socket.getInputStream());

　　　　if(inputStream.available()>0)　　　　{

　　　　　　byte[] recData = new byte[inputStream.available()];　　　　　　inputStream.read(recData);

　　　　　　String iText=new String(recData,"utf-8");

　　　　  }

    }catch (Exception e){

}

（4）断线重连

当保持长时间的连接时，难免会因为网络或其他原因导致客户端与服务端断开连接，所以代码里面应该定时的去检查连接状态，当连接断开时，

应该重新尝试连接服务端。我们这里可以使用socket.sendUrgentData(0xFF);函数来检测，当服务端断开时，连续三次调用此函数会出现异常。

我们可以根据是否出现异常来断定与服务器的连接情况。

try {    socket.sendUrgentData(0xFF);}catch (Exception e){    socket.close();        //关闭套接字，重新创建新的并调用connect函数重新连接    socket = new Socket();}

以下贴出TcpHelper类的具体代码：

public class TcpHelper{    private Socket socket;               private BufferedWriter  bufferedWriter;    private DataInputStream inputStream;    private boolean NeedStop;    private InetSocketAddress SerAddr;    public  String ErrMsg;    private ReadThread readThread;           //读取数据线程    private OnReceiveEvent receiveEvent;     //此事件用于当接收到数据时向主线程通知接收到的数据    private long LastCheckTime;    public static interface OnReceiveEvent{        public  void ReceiveBytes(byte[] iData);        public  void ReceiveString(String iData);    }    public enum EDataType{EDT_BYTE,EDT_STRING};    private EDataType dataType;    public TcpHelper(String HostIp,int HostPort) {        try {            LastCheckTime=System.currentTimeMillis();            readThread =new ReadThread();            NeedStop=false;            SerAddr =  new InetSocketAddress(HostIp,HostPort);            NeedStop=false;            socket = new Socket();            readThread.start();        }catch (Exception e)        {            ErrMsg=e.getMessage();        }    }    public void SendString(String iText){       //发送字符串        dataType=EDataType.EDT_STRING;        toSend(iText);    }    public void SendBytes(byte[] iBuf){     //发送字节流指令        dataType=EDataType.EDT_BYTE;        String iText = new  String(iBuf);        toSend(iText);    }    //发送数据线程    private void toSend(final String iText){        new Thread(                new Runnable() {                    @Override                    public void run() {                        try {                            bufferedWriter.write(iText);                            bufferedWriter.flush();                        } catch (Exception e) {                        }                    }                }        ).start();    }    public boolean isConnected(){        return socket.isConnected();    }    //设置通知事件    public void setReceiveEvent(OnReceiveEvent iEvent){        receiveEvent=iEvent;    }    //读取线程    private class ReadThread extends Thread{        @Override        public void run() {            while (!NeedStop){                try {                    if (!socket.isConnected() || socket.isClosed()){                        socket.connect(SerAddr,3000);                        if(bufferedWriter==null)                            bufferedWriter =new BufferedWriter(new OutputStreamWriter( socket.getOutputStream(),"utf-8"));                        if(inputStream==null)                            inputStream = new DataInputStream(socket.getInputStream());                    }                    else {                        if(inputStream.available()>0){                            byte[] recData = new byte[inputStream.available()];                            inputStream.read(recData);                            if(receiveEvent!=null)                            {                                if(dataType==EDataType.EDT_BYTE) {                                    receiveEvent.ReceiveBytes(recData);                                }                                else {                                    String s=new String(recData,"utf-8");                                    receiveEvent.ReceiveString(s);                                }                            }                        }                        if (System.currentTimeMillis()-LastCheckTime>5000)                        {                            try {                                LastCheckTime=System.currentTimeMillis();                                socket.sendUrgentData(0xFF);                            }catch (Exception e){                                socket.close();                                socket = new Socket();                                bufferedWriter=null;                                inputStream =null;                            }                        }                    }

                }catch (Exception e){

                }            }        }    }}

测试Tcp连接的Activity代码：

import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.widget.EditText;import android.widget.TextView;

public class TcpFormActivity extends Activity {    private TcpHelper tcpHelper;    private String SerIp;    private int SerPort;    private EditText InputMsg;    private TextView RecMsg;    private String TcpRecData;    private MyHandler handler;    private TcpReceive tcpReceive;    @Override    protected void onCreate(Bundle saveInstanceState){        super.onCreate(saveInstanceState);        setContentView(R.layout.activity_tcpform);        RecMsg = (TextView)findViewById(R.id.TVTcpData);        InputMsg =  (EditText)findViewById(R.id.EdtTcpMsg);    }    public class TcpReceive implements TcpHelper.OnReceiveEvent{        public  synchronized void ReceiveBytes(byte[] iData){        }        public  synchronized  void ReceiveString(String iData){            TcpRecData=iData;            Message msg=new Message();            msg.what=1;            handler.sendMessage(msg);        }    }    class MyHandler extends Handler {        public MyHandler() {        }        @Override        public void handleMessage(Message msg) {            switch (msg.what) {                case 1:                    RecMsg.append(TcpRecData);  //接收到数据显示到TextView上                    break;            }            super.handleMessage(msg);        }    }    public void onConnectClick(View view){        if(tcpHelper==null)        {            SerIp = ((EditText)findViewById(R.id.EdtTcpSerIp)).getText().toString();            SerPort =Integer.parseInt(((TextView)findViewById(R.id.EdtTcpPort)).getText().toString());            tcpHelper = new TcpHelper(SerIp,SerPort);            tcpReceive = new TcpReceive();            tcpHelper.setReceiveEvent(tcpReceive);            handler = new MyHandler();        }    }    public void onSendMsgClick(View view){        try {            String iText=InputMsg.getText().toString();            tcpHelper.SendString(iText);        }catch (Exception e)        {

        }    }}