通过蓝牙从 Java 服务器向 Android 客户端发送文本 [英] Send text through Bluetooth from Java Server to Android Client

问题描述

首先...不要将我重定向到蓝牙聊天，我已经完全阅读了.

First of all... don't redirect me to Bluetooth Chat and I have fully read it.

我有一个 Android 客户端，它可以正确地建立与服务器的连接，而且我最多可以将文本发送到我电脑中的服务器并正确显示，但我不能做相反的操作，从服务器到客户端并显示在我的 android 应用程序中.

I have an Android Client which stablishes the connection properly with the server, and what's most I can send text to the server in my pc and show it correctly, but I can't do the opposite action, send a simple string from the server to the client and show it in my android app.

我不想实现聊天只是为了展示 BT 通信在 Java 服务器和 Android 客户端之间是如何工作的.

I don't want to implement a chat is just to show how BT communication works between a Java Server and Android Client.

为了方便:

我在服务器类中的 startServer() 方法的末尾发送文本.

我尝试在 onPause() 开始时从服务器读取文本.

**

**.

代码如下:

Android BT 客户端:

Android BT Client:

/*...libraries here...*/
  public class ConnectTest extends Activity {
  TextView out;
  private static final int REQUEST_ENABLE_BT = 1;
  private BluetoothAdapter btAdapter = null;
  private BluetoothSocket btSocket = null;
  private OutputStream outStream = null;

  // Well known SPP UUID
  private static final UUID MY_UUID =
      UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");

  // Insert your server's MAC address
  private static String address = "00:10:60:AA:B9:B2";

  /** Called when the activity is first created. */
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    out = (TextView) findViewById(R.id.out);

    out.append("
...In onCreate()...");

    btAdapter = BluetoothAdapter.getDefaultAdapter();
    CheckBTState();
  }

  public void onStart() {
    super.onStart();
    out.append("
...In onStart()...");
  }

  public void onResume() {
    super.onResume();

    out.append("
...In onResume...
...Attempting client connect...");

    // Set up a pointer to the remote node using it's address.
    BluetoothDevice device = btAdapter.getRemoteDevice(address);

    // Two things are needed to make a connection:
    //   A MAC address, which we got above.
    //   A Service ID or UUID.  In this case we are using the
    //     UUID for SPP.
    try {
      btSocket = device.createRfcommSocketToServiceRecord(MY_UUID);
    } catch (IOException e) {
      AlertBox("Fatal Error", "In onResume() and socket create failed: " + e.getMessage() + ".");
    }

    // Discovery is resource intensive.  Make sure it isn't going on
    // when you attempt to connect and pass your message.
    btAdapter.cancelDiscovery();

    // Establish the connection.  This will block until it connects.
    try {
      btSocket.connect();
      out.append("
...Connection established and data link opened...");
    } catch (IOException e) {
      try {
        btSocket.close();
      } catch (IOException e2) {
        AlertBox("Fatal Error", "In onResume() and unable to close socket during connection failure" + e2.getMessage() + ".");
      }
    }

    // Create a data stream so we can talk to server.
    out.append("
...Sending message to server...");
    String message = "Hello from Android.
";
    out.append("

...The message that we will send to the server is: "+message);

    try {
      outStream = btSocket.getOutputStream();
    } catch (IOException e) {
      AlertBox("Fatal Error", "In onResume() and output stream creation failed:" + e.getMessage() + ".");
    }

    byte[] msgBuffer = message.getBytes();
    try {
      outStream.write(msgBuffer);
    } catch (IOException e) {
      String msg = "In onResume() and an exception occurred during write: " + e.getMessage();
      if (address.equals("00:00:00:00:00:00")) 
        msg = msg + ".

Update your server address from 00:00:00:00:00:00 to the correct address on line 37 in the java code";
      msg = msg +  ".

Check that the SPP UUID: " + MY_UUID.toString() + " exists on server.

";

      AlertBox("Fatal Error", msg);       
    }
  }

  public void onPause() {
    super.onPause();

    //out.append("
...Hello
");
    InputStream inStream;
    try {
        inStream = btSocket.getInputStream();
        BufferedReader bReader=new BufferedReader(new InputStreamReader(inStream));
        String lineRead=bReader.readLine();
        out.append("
..."+lineRead+"
");

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    out.append("
...In onPause()...");



    if (outStream != null) {
      try {
        outStream.flush();
      } catch (IOException e) {
        AlertBox("Fatal Error", "In onPause() and failed to flush output stream: " + e.getMessage() + ".");
      }
    }

    try     {
      btSocket.close();
    } catch (IOException e2) {
      AlertBox("Fatal Error", "In onPause() and failed to close socket." + e2.getMessage() + ".");
    }
  }

  public void onStop() {
    super.onStop();
    out.append("
...In onStop()...");
  }

  public void onDestroy() {
    super.onDestroy();
    out.append("
...In onDestroy()...");
  }

  private void CheckBTState() {
    // Check for Bluetooth support and then check to make sure it is turned on

    // Emulator doesn't support Bluetooth and will return null
    if(btAdapter==null) { 
      AlertBox("Fatal Error", "Bluetooth Not supported. Aborting.");
    } else {
      if (btAdapter.isEnabled()) {
        out.append("
...Bluetooth is enabled...");
      } else {
        //Prompt user to turn on Bluetooth
        Intent enableBtIntent = new Intent(btAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
      }
    }
  }

  public void AlertBox( String title, String message ){
    new AlertDialog.Builder(this)
    .setTitle( title )
    .setMessage( message + " Press OK to exit." )
    .setPositiveButton("OK", new OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {
          finish();
        }
    }).show();
  }
}

和 Java BT 服务器:

and the Java BT Server:

    import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import javax.bluetooth.*;
import javax.microedition.io.*;

/**
* Class that implements an SPP Server which accepts single line of
* message from an SPP client and sends a single line of response to the client.
*/
public class SimpleSPPServer {

    //start server
    private void startServer() throws IOException{

        //Create a UUID for SPP
        UUID uuid = new UUID("1101", true);
        //Create the servicve url
        String connectionString = "btspp://localhost:" + uuid +";name=Sample SPP Server";

        //open server url
        StreamConnectionNotifier streamConnNotifier = (StreamConnectionNotifier)Connector.open( connectionString );

        //Wait for client connection
        System.out.println("
Server Started. Waiting for clients to connect...");
        StreamConnection connection=streamConnNotifier.acceptAndOpen();

        RemoteDevice dev = RemoteDevice.getRemoteDevice(connection);
        System.out.println("Remote device address: "+dev.getBluetoothAddress());
        System.out.println("Remote device name: "+dev.getFriendlyName(true));

        //read string from spp client
        InputStream inStream=connection.openInputStream();
        BufferedReader bReader=new BufferedReader(new InputStreamReader(inStream));
        String lineRead=bReader.readLine();
        System.out.println(lineRead);

        //send response to spp client
        OutputStream outStream=connection.openOutputStream();
        BufferedWriter bWriter=new BufferedWriter(new OutputStreamWriter(outStream));
        bWriter.write("Response String from SPP Server
");

        /*PrintWriter pWriter=new PrintWriter(new OutputStreamWriter(outStream));
        pWriter.write("Response String from SPP Server
");
        pWriter.flush();
        pWriter.close();*/

        streamConnNotifier.close();

    }


    public static void main(String[] args) throws IOException {

        //display local device address and name
        LocalDevice localDevice = LocalDevice.getLocalDevice();
        System.out.println("Address: "+localDevice.getBluetoothAddress());
        System.out.println("Name: "+localDevice.getFriendlyName());

        SimpleSPPServer sampleSPPServer=new SimpleSPPServer();
        sampleSPPServer.startServer();

    }
}

解决方案:这只是服务器端的一个小改动.我不知道为什么，但不是使用 BufferedWrite 在套接字中写入，我们需要使用 PrinterWriter 来执行此操作.我添加了修改后的那段代码:

Solution: It's just a small change in the server side. I don't know why but instead of using BufferedWrite to write in the socket, we need to use PrinterWriter to do so. I add that piece of code modified:

BT 服务器:

    ....
    //read string from spp client
    InputStream inStream=connection.openInputStream();
    BufferedReader bReader=new BufferedReader(new InputStreamReader(inStream));
    String lineRead=bReader.readLine();
    System.out.println(lineRead);

    //send response to spp client
    OutputStream outStream=connection.openOutputStream();
    PrintWriter pWriter=new PrintWriter(new OutputStreamWriter(outStream));
    pWriter.write("Response String from SPP Server
");
    pWriter.flush();

    pWriter.close();

    streamConnNotifier.close();
    ...

推荐答案

看起来您的 BufferedWriter 缓存没有被刷新，数据只是保留在缓冲区中而没有被发送.在 bWriter.write() 之后调用 bWriter.flush() 应该可以解决问题并导致数据刷新到输出流.您也可以考虑更改您的代码以遵循此:

It looks like your BufferedWriter cache was not being flushed, the data was simply remaining in the buffer without being sent. Calling bWriter.flush() after your bWriter.write() should fix the issue and cause the data to be flushed to the output stream. You can also consider changing your code to follow this:

PrintWriter pWriter = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outStream)));

这将导致 PrintWriter 输出被缓冲，而不是立即写入输出流，这可能是低效的.

This will cause the PrintWriter output to be buffered, instead of being written immediately to the output stream, which can be inefficient.

不过，出于您的目的，省略 BufferedWriter 应该没问题，因为您很可能希望立即刷新到输出流(PrintWriter 这样做).

For your purposes though, omitting the BufferedWriter should be fine, as you will most likely want an immediate flush to the output stream (which PrintWriter does).

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