Android登录时密码保护功能

package com.itcast.test03;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.ParseException;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONObject;
import android.os.Build;
import android.os.Bundle;
import android.os.StrictMode;
import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.text.TextUtils;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnFocusChangeListener;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;


public class MainActivity extends Activity implements OnClickListener {
 private EditText et_username;
 private EditText et_userPsd;
 private Button login;
 private Button signUp;
 private CheckBox save;
 private String user,pass;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);  
  setContentView(R.layout.activity_main);
  et_username = (EditText)findViewById(R.id.et_number);
  et_userPsd = (EditText)findViewById(R.id.et_password);
  login=(Button)findViewById(R.id.login);
  signUp=(Button)findViewById(R.id.signUp);
  save = (CheckBox)findViewById(R.id.save);
  save.setOnClickListener(new CheckBox.OnClickListener(){
   public void onClick(View v) {
    SharedPreferences pre = getSharedPreferences("loginvalue",
             MODE_WORLD_WRITEABLE);
    pass = MD5( et_userPsd.getText().toString());
    user = et_username.getText().toString();
    if (!pass.equals("") && !user.equals("")) {
       pre.edit().putString("username",
         et_username.getText().toString())
         .putString("password", encryptmd5(pass)).commit();
    Toast.makeText(getApplicationContext(),"保存成功!",
    Toast.LENGTH_SHORT).show();
    } else{
    Toast.makeText(getApplicationContext(),"密码不能为空！",
    Toast.LENGTH_LONG).show();
  }
    }
  });
  login.setOnClickListener(new Button.OnClickListener() {
    
   @Override
   public void onClick(View v) {
    
   SharedPreferences sp = getSharedPreferences("loginvalue",MODE_WORLD_READABLE);
   String loginuser = sp.getString("username",null);
   String loginpass = sp.getString("password",null);
    
   user = et_username.getText().toString();
   pass = et_userPsd.getText().toString();
    
   String passmd5 = MD5(pass);
   String encryptmd5 = encryptmd5(passmd5);
    
   System.out.println("username="+ loginuser
   + "-------------password="+ loginpass);
   System.out.println("user=="+ user
   + "-------------encryptmd5=="+ encryptmd5);
   if (!user.equals("") && !pass.equals("")) {
   if (user.equals(loginuser) && encryptmd5.equals(loginpass)) {
   Intent intent = new Intent();
   intent.setClass(MainActivity.this, StudentMainActivity.class);
   MainActivity.this.startActivity(intent);
   finish();
   } else{
   Toast.makeText(getApplicationContext(),"密码是错误的！",
   Toast.LENGTH_LONG).show();
   }
   } else{
   Toast.makeText(getApplicationContext(),"密码不能为空！",
   Toast.LENGTH_LONG).show();
   }
    
   }
    
   });
  initWidget();//
  }
 private void initWidget()
 {
  
  login.setOnClickListener(this);
  signUp.setOnClickListener(this);
  et_username.setOnFocusChangeListener(new OnFocusChangeListener()
  {

   @Override
   public void onFocusChange(View v, boolean hasFocus) {
    // TODO Auto-generated method stub
    if(!hasFocus){
     String username=et_username.getText().toString().trim();
     if(username.length()<4){
      Toast.makeText(MainActivity.this, "用户名不能小于4个字符", Toast.LENGTH_SHORT);
     }
    }
   }
   
  });
  et_userPsd.setOnFocusChangeListener(new OnFocusChangeListener()
  {

   @Override
   public void onFocusChange(View v, boolean hasFocus) {
    // TODO Auto-generated method stub
    if(!hasFocus){
     String password=et_userPsd.getText().toString().trim();
     if(password.length()<4){
      Toast.makeText(MainActivity.this, "密码不能小于4个字符", Toast.LENGTH_SHORT);
     }
    }
   }
   
  });
 }
 

 public void onClick(View v) {
  // TODO Auto-generated method stub
  switch(v.getId())
  {
  case R.id.login:
   if(checkEdit())
   {
    login();
   }   
   break;
  case R.id.signUp:
   Intent intent2=new Intent(MainActivity.this,SignUp.class);
   startActivity(intent2);
   break;
  }
 }
 
 private boolean checkEdit(){
  if(et_username.getText().toString().trim().equals("")){
   Toast.makeText(MainActivity.this, "用户名不能为空", Toast.LENGTH_SHORT).show();
   Intent intent=new Intent(MainActivity.this,StudentMainActivity.class);
   startActivity(intent);
  }else if(et_userPsd.getText().toString().trim().equals("")){
   Toast.makeText(MainActivity.this, "密码不能为空", Toast.LENGTH_SHORT).show();
  }else{
   return true;
  }
  return false;
 }
 
 private void login(){
  //这个网址需要改动
  String httpUrl="http://192.168.1.102:8080/web-test/login.jsp";
  HttpPost httpRequest=new HttpPost(httpUrl);
  List params=new ArrayList();
  params.add(new BasicNameValuePair("username",et_username.getText().toString().trim()));
  params.add(new BasicNameValuePair("password",et_userPsd.getText().toString().trim()));
  HttpEntity httpentity = null;
  try {
   httpentity = new UrlEncodedFormEntity(params,"utf8");
  } catch (UnsupportedEncodingException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  httpRequest.setEntity(httpentity);
  HttpClient httpclient=new DefaultHttpClient();
  HttpResponse httpRespOnse= null;
  try {
   httpRespOnse= httpclient.execute(httpRequest);
  } catch (ClientProtocolException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  if(httpResponse.getStatusLine().getStatusCode()==200)
  {
   String strResult = null;
   try {
    strResult = EntityUtils.toString(httpResponse.getEntity());
   } catch (ParseException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
   Toast.makeText(MainActivity.this, strResult, Toast.LENGTH_SHORT).show();
   Intent intent=new Intent(MainActivity.this,StudentMainActivity.class);
   startActivity(intent);
  }
  else
   
  {
   Toast.makeText(MainActivity.this, "登录失败！", Toast.LENGTH_SHORT).show();
  }
  
 }
 public static String MD5(String str){ 
  MessageDigest md5 = null; 
 try {
  md5 = MessageDigest.getInstance("MD5");
 } catch (NoSuchAlgorithmException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  return "";
 }
  char[] charArray = str.toCharArray();
  byte[] byteArray = new byte[charArray.length];
  for (int i = 0; i