我正在编写一个远程桌面应用程序，为此我需要将屏幕截图从桌面发送到安卓手机。正在创建屏幕截图，我想也可以在 DataOutputstrean 上写入，但在客户端它无法正确读取。以下是代码：
服务器.java：
import java.awt.AWTException;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import javax.imageio.ImageIO;
公共类主要{
private static BufferedImage screenshot;
private static Robot robot;
private static BufferedWriter outToClient;
private static FileInputStream inStream;
private static DataOutputStream outStream;
private static int screenWidth;
private static int screenHeight;
private static ServerSocket serverSocket;
private static Socket clientSocket;
private static InputStreamReader inputStreamReader;
private static BufferedReader bufferedReader;
private static String message;
private static Thread screenThread;
public static void main(String[] args) {
try {
serverSocket = new ServerSocket(21112); //Server socket
} catch (IOException e) {
System.out.println("Could not listen on port: 21111");
}
System.out.println("Server started. Listening to the port 21111");
while (true) {
try {
clientSocket = serverSocket.accept(); //accept the client connection
System.out.println("accepted");
inputStreamReader = new InputStreamReader(clientSocket.getInputStream());
bufferedReader = new BufferedReader(inputStreamReader); //get the client message
message = bufferedReader.readLine();
System.out.println(message);
Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize();
robot = new Robot();
System.out.println("After robot object in thread");
screenWidth = dimension.width;
screenHeight = dimension.height;
Rectangle screen = new Rectangle(screenWidth, screenHeight);
screenshot = robot.createScreenCapture(screen);
File file = new File("C:/Users/hp/Desktop/screenshot.png");
ImageIO.write(screenshot, "jpeg", file);
System.out.println("After ImageIO.write");
inStream = new FileInputStream(file);
byte[] buffer = new byte[4096];
System.out.println("After Fileinstram");
// prepare client for receiving the screenshot
outToClient = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
outToClient.write("#!<cmd>screenshot");
System.out.println("After preparing client to read the image file");
outToClient.newLine();
outToClient.flush();
// send the screenshot to the client
outStream = new DataOutputStream(clientSocket.getOutputStream());
System.out.println("After Datastream output obj");
int n;
int i = 0;
while((n = inStream.read(buffer)) != -1) {
System.out.println("In while");
i++;
System.out.println(i + ". Byte[" + n + "]");
outStream.write(buffer, 0, n);
outStream.flush();
}
} catch(AWTException e1) {
System.out.println("AWT: " + e1.getMessage().toString());
} catch(IOException e2) {
System.out.println("IO: " + e2.getMessage().toString());
} finally {
try {
// close streams and socket
inStream.close();
outToClient.close();
clientSocket.close();
} catch(IOException e) {
System.out.println(e.getMessage().toString());
}
}
//inputStreamReader.close();
// clientSocket.close();
}
}
}
Client.java（安卓客户端）：
package roman10.tutorial.tcpcommclient;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
public class TcpClient extends Activity {
/** Called when the activity is first created. */
private static Socket s;
private Handler handler;
private BufferedReader inFromServer;
private DataInputStream inStream;
private ByteArrayOutputStream content;
private FileOutputStream fileOutStream;
private final String TAG = "xxx";
private final int SERVER_TRANSFER_PORT = 21115;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.e("TcpClient" , "in creaste");
runTcpClient();
// finish();
}
private static final int TCP_SERVER_PORT = 21115;
private void runTcpClient() {
try {
while( true) {
s = new Socket("10.4.9.169", TCP_SERVER_PORT);
Log.e("TcpClient" , "socket created");
BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
//send output msg
String outMsg = "TCP connectingfghg to " + System.getProperty("line.separator") ;
out.write(outMsg);
out.flush();
Log.e("TcpClient", "sent: " + outMsg);
inFromServer = new BufferedReader(new InputStreamReader(s.getInputStream()));
Log.d(TAG, "ServerTransferThread: bufferedReader()");
String message = "";
if((message = inFromServer.readLine()) != null) {
if(message.equals("#!<cmd>screenshot")) {
receiveScreenshot(s);
}
}
}
/*
Thread cclientscreen = new Thread(new ClientTransferThread(new Handler()));
cclientscreen.start();*/
//accept server response
//String inMsg = in.readLine() + System.getProperty("line.separator");
//Log.e("TcpClient", "received: " + inMsg);
//close connection
}catch (UnknownHostException e) {
e.printStackTrace();
}catch(IOException e) {
Log.e(TAG, "ClientTransferThread 1: " + e.getMessage().toString());
} finally {
try {
inFromServer.close();
//s.close();
//serverTransferSocket.close();
} catch (IOException e) {
Log.e(TAG, "ClientTransferThread 2: " + e.getMessage().toString());
}
}
}
public static Socket getS() {
return s;
}
public static void setS(Socket s) {
TcpClient.s = s;
}
private void receiveScreenshot(Socket socketX) {
Log.d(TAG, "ClientTransferThread: receiveScreenshot()");
try {
Log.d(TAG, "receiveScreenshot(): receiving screenshot");
// handler.sendMessage(buildMessage("> Receiving screenshot.."));
inStream = new DataInputStream(socketX.getInputStream());
Log.d(TAG, "receiveScreenshot(): after datastream");
byte[] buffer = new byte[4096];
content = new ByteArrayOutputStream();
int n;
while((n = inStream.read()) != -1) {
content.write(buffer, 0, n);
Log.d(TAG, "rcvscrnshot: in while");// HERE I "OUT OF MEMORY"
content.flush();
}
Log.d(TAG, "rcvscrnshot: outside while");
// File directory = new File(ServerActivity.APP_FOLDER_PATH);
//File screenshot = new File(Environment.getExternalStorageState() + "/" + "screenshot.png");
String path = "/storage/sdcard/picshello";
File outputDir= new File(path);
Log.d(TAG, "rcvscrnshot: after outfilepath dir");
outputDir.mkdirs();
Log.d(TAG, "rcvscrnshot: mkdir");
File screenshot = new File(path+"/"+"screenshot.jpeg");
Log.d(TAG, "rcvscrnshot: opening png file");
// FileOutputStream out = new FileOutputStream(screenshot);
//bmp.compress(Bitmap.CompressFormat.PNG, 100, out);
// if(!directory.exists())
// directory.mkdirs();
/*
if(!screenshot.exists()) {
screenshot.createNewFile();
}
else {
screenshot.delete();
screenshot.createNewFile();
}
*/
Log.d(TAG, "rcvscrnshot: file created");
fileOutStream = new FileOutputStream(screenshot);
Log.d(TAG, "rcvscrnshot: fileoutstream");
Bitmap bmp = BitmapFactory.decodeByteArray(content.toByteArray(), 0, content.size());
Log.d(TAG, "rcvscrnshot: bmp created");
bmp.compress(Bitmap.CompressFormat.JPEG, 100, fileOutStream);
Log.d(TAG, "rcvscrnshot: bmp compressed");
//handler.sendMessage(buildMessage("> Screenshot received sucessfully!"));
} catch(IOException e1) {
Log.e(TAG, "ClientTransferThread 3: " + e1.getMessage().toString());
} finally {
try {
inStream.close();
content.close();
fileOutStream.close();
socketX.close();
} catch (IOException e) {
Log.e(TAG, "ClientTransferThread 4: " + e.getMessage().toString());
}
}
}
private Message buildMessage(String text) {
Log.d(TAG, "ClientTransferThread: buildMessage()");
Message msg = handler.obtainMessage();
Bundle bundle = new Bundle();
bundle.putString("MESSAGE", text);
msg.setData(bundle);
return msg;
}
/*
//replace runTcpClient() at onCreate with this method if you want to run tcp client as a service
private void runTcpClientAsService() {
Intent lIntent = new Intent(this.getApplicationContext(), TcpClientService.class);
this.startService(lIntent);
}
*/
}
Logcat（客户端）：
... // After creating socket it prints "in while" many times
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: in while
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: in while
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: outside while
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: after outfilepath dir
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: mkdir
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: opening jpeg file
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: file created
11-03 00:11:05.373: D/xxx(7134): rcvscrnshot: fileoutstream
11-03 00:11:05.453: D/dalvikvm(7134): GC_FOR_ALLOC freed 825K, 43% free 11154K/19452K, paused 80ms, total 80ms
11-03 00:11:05.573: I/dalvikvm-heap(7134): Grow heap (frag case) to 18.806MB for 8222931-byte allocation
11-03 00:11:05.673: D/dalvikvm(7134): GC_FOR_ALLOC freed 0K, 31% free 19185K/27484K, paused 80ms, total 80ms
11-03 00:11:05.693: D/skia(7134): --- SkImageDecoder::Factory returned null
11-03 00:11:05.693: D/xxx(7134): rcvscrnshot: bmp created
11-03 00:11:05.713: D/AndroidRuntime(7134): Shutting down VM
11-03 00:11:05.713: W/dalvikvm(7134): threadid=1: thread exiting with uncaught exception (group=0xb1a99ba8)
11-03 00:11:05.733: E/AndroidRuntime(7134): FATAL EXCEPTION: main
11-03 00:11:05.733: E/AndroidRuntime(7134): Process: roman10.tutorial.tcpcommclient, PID: 7134
11-03 00:11:05.733: E/AndroidRuntime(7134): java.lang.RuntimeException: Unable to start activity ComponentInfo{roman10.tutorial.tcpcommclient/roman10.tutorial.tcpcommclient.TcpClient}:
java.lang.NullPointerException
11-03 00:11:05.733: E/AndroidRuntime(7134): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
11-03 00:11:05.733: E/AndroidRuntime(7134): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
控制台（服务器）：
Server started. Listening to the port 21111
accepted
TCP connectingfghg to
After robot object in thread
After ImageIO.write
After Fileinstram
After preparing client to read the image file
After Datastream output obj
In while
1. Byte[4096]
In while
..... // Like this till it reads the whole file.
我被困了 2 天，从 stackoverflow 尝试了这段代码（链接：ANDROID - 通过 tcp 套接字从 java 发送屏幕截图到 android）我也得到了同样的错误，但是提到的答案不起作用或者我错误地实现了它。