Android ObjectOutputStream

Question

我需要发送我的服务器java程序(它运行在PC上)电子邮件地址和密码从android应用程序，但当我点击登录按钮服务器没有收到我的消息和应用程序崩溃

这是android代码：

    public class MainActivity extends Activity {

    private TextView tv;
    private Button button;
    private EditText editText1;
    private EditText editText2;
    Socket client;

    private class myTask extends AsyncTask<String, String, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected String doInBackground(String... params) {

           try {
                 client = new Socket("192.168.1.3", 4444);  //connect to server

           }catch (UnknownHostException e){
               return "Host not found";
           }catch (IOException e) {
               return "Exception Caught";
           }
            return null;
        }

        @Override
        protected void onPostExecute(String result) {

            super.onPostExecute(result);   



            if ("Host not found".equalsIgnoreCase(result)){
                Toast.makeText(getApplicationContext(), "Host not found" ,Toast.LENGTH_LONG).show();
            }else if("Exception Caught".equalsIgnoreCase(result)){
                Toast.makeText(getApplicationContext(), "Connection error" ,Toast.LENGTH_LONG).show();
            }else{
                 Toast.makeText(getApplicationContext(), "Connection established" ,Toast.LENGTH_LONG).show();
             }
        }
    }

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tv = (TextView)findViewById(R.id.register);
        button = (Button)findViewById(R.id.login);

        new myTask().execute();

        tv.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View arg0) {
                startActivity(new Intent(MainActivity.this, Register.class));
            }
        });

        button.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View arg0) {
                ObjectInputStream ois = null;
                ObjectOutputStream oos = null;

                try {

                    oos = new ObjectOutputStream(client.getOutputStream());

                    oos.writeUTF("LOGIN");

                    String emailText = editText1.getText().toString();
                    oos.writeUTF(emailText);
                    oos.flush();

                    String passwordText = editText2.getText().toString();
                    oos.writeUTF(passwordText);
                    oos.flush();

                        client.close();

                } catch (IOException ex) {
                    Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);                 
                }

            }

        });


    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

服务器崩溃：

Exception in thread "main" java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:196)
at java.net.SocketInputStream.read(SocketInputStream.java:122)
at java.net.SocketInputStream.read(SocketInputStream.java:210)
at java.io.ObjectInputStream$PeekInputStream.peek(ObjectInputStream.java:2293)
at java.io.ObjectInputStream$BlockDataInputStream.readBlockHeader(ObjectInputStream.java:2473)
at java.io.ObjectInputStream$BlockDataInputStream.refill(ObjectInputStream.java:2543)
at java.io.ObjectInputStream$BlockDataInputStream.read(ObjectInputStream.java:2615)
at java.io.DataInputStream.readUnsignedShort(DataInputStream.java:337)
at java.io.ObjectInputStream$BlockDataInputStream.readUnsignedShort(ObjectInputStream.java:2808)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:2864)
at java.io.ObjectInputStream.readUTF(ObjectInputStream.java:1072)

android应用程序日志：

    06-02 10:42:56.948: E/AndroidRuntime(5383): FATAL EXCEPTION: main
06-02 10:42:56.948: E/AndroidRuntime(5383): java.lang.NullPointerException
06-02 10:42:56.948: E/AndroidRuntime(5383):     at com.example.social_network.MainActivity$2.onClick(MainActivity.java:106)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at android.view.View.performClick(View.java:4240)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at android.view.View$PerformClick.run(View.java:17721)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at android.os.Handler.handleCallback(Handler.java:730)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at android.os.Handler.dispatchMessage(Handler.java:92)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at android.os.Looper.loop(Looper.java:137)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at android.app.ActivityThread.main(ActivityThread.java:5103)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at java.lang.reflect.Method.invokeNative(Native Method)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at java.lang.reflect.Method.invoke(Method.java:525)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
06-02 10:42:56.948: E/AndroidRuntime(5383):     at dalvik.system.NativeStart.main(Native Method)

我需要使用ObjectOutputStream，因为服务器被设置为接收这个object..what，对吗？谢谢

Answer 1

虽然我不完全确定为什么NullPointerException会崩溃，但我不认为ObjectOutputStream是为在同一流上发送多个对象而设计的。我建议使用单个类来保存数据，而不是使用多个String。

另外，我不使用默认的ObjectOutputStream，而是使用KryoNet序列化库，因为它节省了使用AsyncTasks (默认情况下是异步的和基于侦听器的)的工作量，并且使这个过程更加容易。它也是桌面和Android之间的跨平台。

https://github.com/EsotericSoftware/kryonet

它的工作方式是必须在服务器和客户端的Kryo对象中注册要发送的类，然后可以使用sendTCP( object )命令发送数据。反序列化为对象是自动的，有关详细信息，请参阅网站。使用起来真的很简单！:)