Java客户端/服务器编程 - 用于从Android设备读取数据的BufferedReader将无法在客户端运行，但将在服务器端运行

Question

我正在编写一个示例Java Server / Android Client程序，以学习如何在Android上使用套接字。这是一套简单的程序;客户端向服务器发送一串文本，服务器将其回送给客户端。服务器使用的是直接运行的Java，客户端是使用Jelly Bean版本系统的Android智能手机。虽然我可以让Android设备作为服务器运行，但我很难让它作为客户端工作。

我的服务器代码如下：

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;

public class TCPIPServer3
{
    public static void main(String argv[]) throws Exception 
    { 
        // Declaration Section:
        // Declare a server socket and a client socket for the server
        // Declare an input and an output stream
        ServerSocket echoServer = null;
        String line;
        DataInputStream is;
        BufferedReader br;
        PrintStream os;
        Socket clientSocket = null;

        // Try to open a server socket on port 9999
        // Note that we can't choose a port less than 1023 if we are not
        // privileged users (root)
        try {
            echoServer = new ServerSocket(9999);
        }
        catch (IOException e) {
            System.out.println(e);
        }

        // Create a socket object from the ServerSocket to listen and accept
        // connections.
        // Open input and output streams
        try {
            clientSocket = echoServer.accept();
            is = new DataInputStream(clientSocket.getInputStream());
            br = new BufferedReader(new InputStreamReader(is));
            os = new PrintStream(clientSocket.getOutputStream());
            // As long as we receive data, echo that data back to the client.
            while (true)
            {
                line = br.readLine();
                System.out.println(line);
                os.println(line);
                os.flush();
            }
        }
        catch (IOException e) {
            System.out.println(e);
        }
    }
}

我的客户端代码如下：

package com.example.androidtcpclient3;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class ClientActivity extends Activity {

       private Button bt;
       private TextView tv;
       private Socket socket;
       private String serverIpAddress = "10.0.2.2";
       //private String serverIpAddress = "10.1.200.100";
       private static final int REDIRECTED_SERVERPORT = 9999;

       @Override
       public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.client);
          bt = (Button) findViewById(R.id.myButton);
          tv = (TextView) findViewById(R.id.myTextView);
          Thread cThread = new Thread(new ClientThread());
          cThread.start();
       }

       public class ClientThread implements Runnable {
           public void run() {
              try {
                     InetAddress serverAddr = InetAddress.getByName(serverIpAddress);
                     socket = new Socket(serverAddr, REDIRECTED_SERVERPORT);
                  } catch (UnknownHostException e1) {
                     e1.printStackTrace();
                  } catch (IOException e1) {
                     e1.printStackTrace();
                  }
              bt.setOnClickListener(new OnClickListener() {
                  public void onClick(View v) {
                     try {
                        String line;

                        DataInputStream is;
                        BufferedReader br;
                        PrintWriter out;         

                        EditText et = (EditText) findViewById(R.id.EditText01);
                        String str = et.getText().toString();
                        out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true);
                        out.println(str);
                        Log.d("Client", "Client sent message");

                        is = new DataInputStream(socket.getInputStream());
                        br = new BufferedReader(new InputStreamReader(is));
                        line = br.readLine();                       
                        tv.setText(line);
                     } catch (UnknownHostException e) {
                        tv.setText("Error1");
                        e.printStackTrace();
                     } catch (IOException e) {
                        tv.setText("Error2");
                        e.printStackTrace();
                     } catch (Exception e) {
                        tv.setText("Error3");
                        e.printStackTrace();
                     }
                  }
               });
           }
       }
}

我无法让程序执行语句“line = br.readLine（）;”在Android客户端上。出于某种原因，每次在代码中到达时，此语句总是抛出异常。在客户端程序的执行中，这会导致字符串“Error3”被写入客户端的TextView小部件。但是，我已经能够确认服务器可以从客户端成功读取数据。 readLine（）方法似乎显示客户端和服务器之间的不对称行为。

任何帮助解决此问题都将不胜感激。

更新：我的堆栈跟踪如下：

07-18 13:56:36.802: W/System.err(2164): android.os.NetworkOnMainThreadException
07-18 13:56:36.832: W/System.err(2164):     at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117)
07-18 13:56:36.842: W/System.err(2164):     at libcore.io.BlockGuardOs.recvfrom(BlockGuardOs.java:163)
07-18 13:56:36.842: W/System.err(2164):     at libcore.io.IoBridge.recvfrom(IoBridge.java:513)
07-18 13:56:36.852: W/System.err(2164):     at java.net.PlainSocketImpl.read(PlainSocketImpl.java:488)
07-18 13:56:36.862: W/System.err(2164):     at java.net.PlainSocketImpl.access$000(PlainSocketImpl.java:46)
07-18 13:56:36.872: W/System.err(2164):     at java.net.PlainSocketImpl$PlainSocketInputStream.read(PlainSocketImpl.java:240)
07-18 13:56:36.882: W/System.err(2164):     at java.io.DataInputStream.read(DataInputStream.java:84)
07-18 13:56:36.882: W/System.err(2164):     at java.io.InputStreamReader.read(InputStreamReader.java:244)
07-18 13:56:36.894: W/System.err(2164):     at java.io.BufferedReader.fillBuf(BufferedReader.java:130)
07-18 13:56:36.902: W/System.err(2164):     at java.io.BufferedReader.readLine(BufferedReader.java:354)
07-18 13:56:36.902: W/System.err(2164):     at com.example.androidtcpclient3.ClientActivity$ClientThread$1.onClick(ClientActivity.java:75)
07-18 13:56:36.912: W/System.err(2164):     at android.view.View.performClick(View.java:4204)
07-18 13:56:36.922: W/System.err(2164):     at android.view.View$PerformClick.run(View.java:17355)
07-18 13:56:36.932: W/System.err(2164):     at android.os.Handler.handleCallback(Handler.java:725)
07-18 13:56:36.932: W/System.err(2164):     at android.os.Handler.dispatchMessage(Handler.java:92)
07-18 13:56:36.942: W/System.err(2164):     at android.os.Looper.loop(Looper.java:137)
07-18 13:56:36.952: W/System.err(2164):     at android.app.ActivityThread.main(ActivityThread.java:5041)
07-18 13:56:36.952: W/System.err(2164):     at java.lang.reflect.Method.invokeNative(Native Method)
07-18 13:56:36.962: W/System.err(2164):     at java.lang.reflect.Method.invoke(Method.java:511)
07-18 13:56:36.972: W/System.err(2164):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-18 13:56:36.972: W/System.err(2164):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-18 13:56:36.983: W/System.err(2164):     at dalvik.system.NativeStart.main(Native Method)