求大神解答 新手遇到的有关socket传输一个类时遇到的有关问题

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Serializable;
import java.net.ServerSocket;
import java.net.Socket;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;


public class ser_test{
		public static void main(String []args)	throws Exception
		{
			
			ServerSocket socketConnection =new ServerSocket(30000);
			System.out.println("start");
			Socket socket=socketConnection.accept();
			System.out.println("建立连接");
			
			ObjectInputStream in=new ObjectInputStream(socket.getInputStream());
			
			
			USER user=(USER) in.readObject();
	
			System.out.println("username"+user.getusername());
			System.out.println("password"+user.getpassword());
			
			
			OutputStream os=socket.getOutputStream();
			os.write("success".getBytes("utf-8"));
			
			os.close();
			socketConnection.close();
			
		}
		
}

package com.related.firstactivity;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Serializable;
import java.net.Socket;
import java.net.UnknownHostException;




import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Lg_activity2 extends Activity{

	private Button login_bt;
	private Button register_bt;
	private EditText input_username;
	private EditText input_password;
	
	
	public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.login_regest);
        
        login_bt=(Button)findViewById(R.id.loginbt);
        register_bt=(Button)findViewById(R.id.register_bt);
        input_password=(EditText) findViewById(R.id.password);
        input_username=(EditText) findViewById(R.id.username);
        
        login_bt.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				Thread loginThread = new Thread(new LoginThread());
				
				loginThread.start();
			}
		});
        
        register_bt.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				Intent intent =new Intent();
				intent.setClass(Lg_activity2.this, Register.class);
				startActivity(intent);
			}
		});
	}


Handler handler= new Handler()
{
	 public void handleMessage(Message msg)
	 {
		 switch(msg.what)
		 {
		 case 0:
			 Toast.makeText(getApplicationContext(), "success", 0).show();
			 Intent intent=new Intent(Lg_activity2.this,MainActivity.class);
			 startActivity(intent);
			 finish();
			 break;
		 case 1:
			 Toast.makeText(getApplicationContext(), "faliure", 0).show();
			 break;
		 }
	 }
};
String loginServer(String username,String password)
{
	String reponseMsg="faliuer";
	try {
		Socket socket=new Socket("192.168.191.2",30000);
		
		
		ObjectOutputStream out=new ObjectOutputStream(socket.getOutputStream());
		
		USER user=new USER(username,password);
		
		out.writeObject(user);
		
		out.flush();
		
		
		BufferedReader br=new BufferedReader(new InputStreamReader(socket.getInputStream()));
		reponseMsg=br.readLine();
		
	
	} catch (UnknownHostException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (IOException e) {