Android中的Socket

1. UDP

(1)访问网络必须添加权限,访问网络必须添加权限,访问网络必须添加权限,重要的事情说三遍。

(2)简述

UDP协议是面向报文的,简单地说,利用UDP访问网络的步骤就是“寄快递”:通过DatagramPacket(快件)把数据和地址打包,然后用DatagramSocket(你)进行数据报的收发,至于中途是怎么传送,那就是快递员的事了,不归我们管(也因此,UCP的传输是不可靠的,可能会出现丢包的情况,跟某些快递简直一毛一样)。

InetAddress:记录访问的host等信息。

DatagramPacket:包装数据和访问地址,相当于一个快件。

DatagramSocket:用于发送和接收数据报,相当于快件的寄件人和收件人。

(3)简单示例

String serverIp = "111.111.111.11"; // 访问主机ip
InetAddress address = InetAddress.getByName(serverIp);
DatagramSocket socket = new DatagramSocket(8888); // 根据需要可在实例化时指定端口号 // 网络操作不能在UI线程进行
new Thread() {
@Override
public void run() {
try {
// 发送数据
String msg = "hello";
byte[] msgBytes = msg.getBytes();
DatagramPacket packet = new DatagramPacket(msgBytes, msgBytes.length, mAddress, mPort);
mSocket.send(packet); // 接收数据
byte[] returnMsgBytes = new byte[1024];
DatagramPacket returnPacket = new DatagramPacket(returnMsgBytes, returnMsgBytes.length, mAddress, mPort);
// receive()方法是阻塞的,会一直等待接收到包
mSocket.receive(returnPacket); String serverMsg = new String(returnPacket.getData(), 0, returnMsgBytes.length);
Log.d("test", serverMsg); } catch (IOException e) {
e.printStackTrace();
}
}
}.start();

从例子里我们可以看到,使用UDP就是打包数据、收发数据包这两步。

2. TCP

(1)还是权限,别忘了

(2)简述

与UDP不同,TCP是面向连接的,通过Socket对象创建连接,拿到一个输入流和一个输出流,然后再关闭连接前,可以一直发送与接收数据。

过程类似打电话,首先你得输入对方的电话号码(访问地址),然后拨通电话(创建连接通道),然后你说话(发送数据),或者听对方说话(接收数据),最后挂断电话(关闭连接)。

TCP创建连接时会经过三次握手,而断开连接时经过四次挥手。

(3)简单示例

try {
// 创建连接
Socket socket = new Socket("111.111.111.11", 8888); // 访问地址111.111.111.11:8888
// 拿到输入流(电话听筒)、输出流(电话话筒)
InputStream inputStream = socket.getInputStream();
OutputStream outputStream = socket.getOutputStream(); final BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(outputStream)); // 接收数据
new Thread() {
@Override
public void run() {
try {
String line;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}.start(); // 发送数据
String line = "test";
bw.write(line);
bw.newLine();
bw.flush(); } catch (IOException e) {
e.printStackTrace();
}

可以看到,与UDP不同,TCP是创建连接后,在断开连接前都可以直接通过输入输出流传输数据,不需要另外将数据打包。

(4)在安卓中应用

Activity:

public class TCPActivity extends AppCompatActivity {

    // 发送消息的按钮
private Button mSendBtn;
// 输入框
private EditText mMsgEt;
// 显示消息内容的文本框
private TextView mContentTv; private TCPClientBiz mBiz = new TCPClientBiz();
private boolean isConnected = false; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); initView();
initEvent(); mBiz.connect(new TCPClientBiz.OnConnectedListener() {
@Override
public void onSucceed() {
// 连接成功
isConnected = true;
}
});
} private void initView() {
mSendBtn = findViewById(R.id.send_btn);
mMsgEt = findViewById(R.id.msg_et);
mContentTv = findViewById(R.id.content_tv);
} private void initEvent() {
mSendBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
final String msg = mMsgEt.getText().toString().trim();
if (!msg.isEmpty()) {
if (isConnected) {
mMsgEt.setText("");
// 发送消息
mBiz.send(msg);
}
}
}
}); // 接收服务器的消息
mBiz.setOnReceivedListener(new TCPClientBiz.OnReceivedListener() {
@Override
public void onReceived(String serverMsg) {
mContentTv.append(formatMsg(serverMsg));
} @Override
public void onError(Exception e) {
Toast.makeText(TCPActivity.this, e.getMessage(), Toast.LENGTH_SHORT).show();
}
});
} private String formatMsg(String msg) {
return msg + "\n";
}
}

业务类:

public class TCPClientBiz {

    private InputStream inputStream;
private OutputStream outputStream; private Handler handler = new Handler(Looper.getMainLooper()); // 异步连接,所以需要一个回调,告知已经连接成功
public void connect(final OnConnectedListener onConnectedListener) {
new Thread() {
@Override
public void run() {
try {
Socket socket = new Socket("169.254.165.37", 9999);
inputStream = socket.getInputStream();
outputStream = socket.getOutputStream();
onConnectedListener.onSucceed(); while (true) {
// 不断接收服务器消息
receive();
} } catch (IOException e) {
e.printStackTrace();
}
}
}.start();
} private void receive() {
try {
BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
final String line;
if ((line = br.readLine()) != null) {
handler.post(new Runnable() {
@Override
public void run() {
if (onReceivedListener != null) {
onReceivedListener.onReceived(line);
}
}
});
}
} catch (final IOException e) {
handler.post(new Runnable() {
@Override
public void run() {
if (onReceivedListener != null) {
onReceivedListener.onError(e);
}
}
});
}
} public void send(final String msg) {
new Thread() {
@Override
public void run() {
try {
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(outputStream));
bw.write(msg);
bw.newLine();
bw.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}.start();
} private OnReceivedListener onReceivedListener; public void setOnReceivedListener(OnReceivedListener onReceivedListener) {
this.onReceivedListener = onReceivedListener;
} // 接收消息接口
public interface OnReceivedListener { void onReceived(String serverMsg); void onError(Exception e);
} // 连接成功接口
public interface OnConnectedListener {
void onSucceed();
}
}

在安卓中运用需要注意一些点:第一,连接是异步,要添加回调,否则可能导致空指针异常;第二,网络操作中老生常谈的问题,UI操作注意不要在子线程中。

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