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)
{
}
}
}