    // 發(fā)送文件
    public void sendFile(int size) {
        new Thread(()->{
            try {
                // 表示發(fā)送文件
                outputStream.write("2".getBytes());
            } catch (IOException e) {
                e.printStackTrace();
            }
            for(int i=0; i<size/SocketUtil.MAX_CHUNK+1; i++) {
                StringBuffer sb = new StringBuffer();
                if (i!=size / SocketUtil.MAX_CHUNK) {
                    for (int j = 0; j < SocketUtil.MAX_CHUNK; j++) {
                        sb.append('a');
                    }
                }
                else if(i==size/SocketUtil.MAX_CHUNK && size%SocketUtil.MAX_CHUNK==0) {
                    break;
                }
                else {
                    for (int j = 0; j < size % SocketUtil.MAX_CHUNK; j++) {
                        sb.append('a');
                    }
                }
                try {
                    SocketUtil.sendInfo("[客戶端]發(fā)送一個數(shù)據(jù)包，大小" + sb.toString().getBytes().length + "B");
                    // 發(fā)送chunk的長度
                    outputStream.write(SocketUtil.intToStr(sb.toString().getBytes().length).getBytes());
                    // 發(fā)送chunk塊
                    outputStream.write(sb.toString().getBytes());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            // 最后發(fā)送000表示結束
            try {
                outputStream.write("000".getBytes());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }).start();
    }

接收二進制流的代碼示例如下

    // 讀取二進制信息
    public static byte[] readBytes(InputStream inputStream, String log) {
        byte[] len = new byte[3];
        byte[] allbytes = new byte[10000];
        int idx = 0;
        try {
            inputStream.read(len);
            // 然后再根據(jù)讀取的長度信息讀取二進制流
            // 只要不是最后一個二進制流就繼續(xù)讀取
            while (SocketUtil.parseLen(len) != 0) {
                byte[] temp = new byte[SocketUtil.parseLen(len)];
                inputStream.read(temp);
                idx = SocketUtil.appendBytes(allbytes, temp, idx);
                String info = "[" + log + "]接收一個數(shù)據(jù)包，大小" + SocketUtil.parseLen(len) + "B";
                SocketUtil.sendInfo(info);
                inputStream.read(len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return SocketUtil.getNewArr(allbytes, idx);
    }

其實我理解的所謂的通信協(xié)議，就是發(fā)送方和接收方都遵守的某種規(guī)則，按照這種規(guī)則發(fā)送和接收數(shù)據(jù)就可以保證數(shù)據(jù)的完整性。

完整的代碼

這段代碼只有四個java文件，非常簡單，只是一個極簡的通信協(xié)議模型。

首先來看一下界面定義

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <EditText
        android:id="@+id/text_file_size"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="請輸入待發(fā)送文件大小"/>
    <Button
        android:id="@+id/button_send"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="發(fā)送文件"/>
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="消息欄："/>
    <TextView
        android:id="@+id/text_info"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout>

然后是MainActivity

public class MainActivity extends AppCompatActivity {
    private EditText text_file_size;
    private Button button_send;
    private TextView text_info;
    private BroadcastReceiver broadcastReceiver;
    private SocketClient socketClient;
    private SocketServer socketServer;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        SocketUtil.context = MainActivity.this;
        // 初始化控件
        initView();
        // 注冊廣播接收器
        register();
        socketServer = new SocketServer();
        socketClient = new SocketClient();
    }
    private void initView() {
        text_file_size = findViewById(R.id.text_file_size);
        button_send = findViewById(R.id.button_send);
        button_send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Integer size = Integer.parseInt(text_file_size.getText().toString());
                socketClient.sendFile(size);
            }
        });
        text_info = findViewById(R.id.text_info);
        text_info.setMovementMethod(new ScrollingMovementMethod());
    }
    private void register() {
        broadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                String info = intent.getStringExtra("info");
                text_info.append(info + "\n");
            }
        };
        IntentFilter filter = new IntentFilter("main.info");
        registerReceiver(broadcastReceiver, filter);
    }
}

我們將需要重復用到的一些代碼都放到工具類中

public class SocketUtil {
    public static Context context;
    // 一次最多傳輸多少字節(jié)
    public static int MAX_CHUNK = 100;
    public static void sendInfo(String info) {
        Intent intent = new Intent("main.info");
        intent.putExtra("info", info);
        context.sendBroadcast(intent);
    }
    // 讀取二進制信息
    public static byte[] readBytes(InputStream inputStream, String log) {
        byte[] len = new byte[3];
        byte[] allbytes = new byte[10000];
        int idx = 0;
        try {
            inputStream.read(len);
            // 然后再根據(jù)讀取的長度信息讀取二進制流
            // 只要不是最后一個二進制流就繼續(xù)讀取
            while (SocketUtil.parseLen(len) != 0) {
                byte[] temp = new byte[SocketUtil.parseLen(len)];
                inputStream.read(temp);
                idx = SocketUtil.appendBytes(allbytes, temp, idx);
                String info = "[" + log + "]接收一個數(shù)據(jù)包，大小" + SocketUtil.parseLen(len) + "B";
                SocketUtil.sendInfo(info);
                inputStream.read(len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return SocketUtil.getNewArr(allbytes, idx);
    }
    // 將int轉成String
    public static String intToStr(int len) {
        StringBuffer sb = new StringBuffer();
        if(len < 100) {
            sb.append("0");
        }
        else if (len < 10) {
            sb.append("00");
        }
        sb.append(Integer.toString(len));
        return sb.toString();
    }
    public static int parseLen(byte[] len) {
        return Integer.parseInt(new String(len, 0, len.length));
    }
    public static int appendBytes(byte[] arr1, byte[] arr2, int st) {
        for(int i=st; i<arr2.length; i++) {
            arr1[i] = arr2[i-st];
        }
        return arr2.length+st;
    }
    public static byte[] getNewArr(byte[] arr, int idx) {
        byte[] newarr = new byte[idx];
        for(int i=0; i<idx; i++) {
            newarr[i] = arr[i];
        }
        return newarr;
    }
}

最后是定義我們的客戶端和服務端

public class SocketClient {
    private final String HOST = "localhost";
    private final int PORT = 50055;
    private Socket socket = null;
    private OutputStream outputStream = null;
    private InputStream inputStream = null;
    public SocketClient() {
        conn();
        while(socket == null) {}
        SocketUtil.sendInfo("服務端連接成功...");
        try {
            outputStream = socket.getOutputStream();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    // 連接服務端
    private void conn() {
        new Thread(()->{
            try {
                socket = new Socket(HOST, PORT);
                inputStream = socket.getInputStream();
                while(true) {
                    // 接收服務端消息0
                    byte[] type = new byte[1];
                    inputStream.read(type);
                    if (new String(type, 0, 1).equals("1")) {
                        byte[] infobytes = SocketUtil.readBytes(inputStream, "客戶端");
                        String info = "[客戶端]接收消息：" + new String(infobytes, 0, infobytes.length);
                        SocketUtil.sendInfo(info);
                        SocketUtil.sendInfo("====================================");
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }).start();
    }
    // 發(fā)送文件
    public void sendFile(int size) {
        new Thread(()->{
            try {
                // 表示發(fā)送文件
                outputStream.write("2".getBytes());
            } catch (IOException e) {
                e.printStackTrace();
            }
            for(int i=0; i<size/SocketUtil.MAX_CHUNK+1; i++) {
                StringBuffer sb = new StringBuffer();
                if (i!=size / SocketUtil.MAX_CHUNK) {
                    for (int j = 0; j < SocketUtil.MAX_CHUNK; j++) {
                        sb.append('a');
                    }
                }
                else if(i==size/SocketUtil.MAX_CHUNK && size%SocketUtil.MAX_CHUNK==0) {
                    break;
                }
                else {
                    for (int j = 0; j < size % SocketUtil.MAX_CHUNK; j++) {
                        sb.append('a');
                    }
                }
                try {
                    SocketUtil.sendInfo("[客戶端]發(fā)送一個數(shù)據(jù)包，大小" + sb.toString().getBytes().length + "B");
                    // 發(fā)送chunk的長度
                    outputStream.write(SocketUtil.intToStr(sb.toString().getBytes().length).getBytes());
                    // 發(fā)送chunk塊
                    outputStream.write(sb.toString().getBytes());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            // 最后發(fā)送000表示結束
            try {
                outputStream.write("000".getBytes());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }).start();
    }
}

public class SocketServer {
    private final int PORT = 50055;
    private ServerSocket serverSocket = null;
    public SocketServer() {
        // 啟動服務端監(jiān)聽
        start();
        while(serverSocket == null) {}
        SocketUtil.sendInfo("服務端啟動...");
    }
    // 啟動服務端監(jiān)聽程序
    private void start() {
        new Thread(()->{
            try {
                serverSocket = new ServerSocket(PORT);
                Socket socket = serverSocket.accept();
                InputStream inputStream = socket.getInputStream();
                OutputStream outputStream = socket.getOutputStream();
                while(true) {
                    byte[] type = new byte[1];
                    inputStream.read(type);
                    String typeinfo = new String(type, 0, 1);
                    if(typeinfo.equals("2")) {
                        byte[] file = SocketUtil.readBytes(inputStream, "服務端");
                        String filetxt = new String(file, 0, file.length);
                        String info = "[服務端]接收完文件，大小" + file.length + "B" + "\n";
                        info = info + "[服務端]具體內(nèi)容如下：" + "\n" + filetxt;
                        SocketUtil.sendInfo(info);
                        // 給客戶端發(fā)送一個響應信息表示接收成功
                        String typetxt = "1";
                        outputStream.write(typetxt.getBytes());
                        String successinfo = "文件接收成功";
                        String lentxt = SocketUtil.intToStr(successinfo.getBytes().length);
                        outputStream.write(lentxt.getBytes());
                        outputStream.write(successinfo.getBytes());
                        outputStream.write("000".getBytes());
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }).start();
    }
}

上述代碼中，服務端只負責接收二進制流，客戶端只負責發(fā)送二進流，并且服務端在接收完二進制流數(shù)據(jù)后，會給服務端返回一個表示接收成功的文字信息。