輸入字符串爲null Base64解碼

Question

我在使用Base64的sharedpreferences中加密了字符串，但解碼出錯。我是加密新手，無法確定logcat錯誤。

logcat的：

11-12 03:57:06.593: W/System.err(20229): java.lang.NullPointerException: Input string was null. 
    11-12 03:57:06.603: W/System.err(20229): at com.SharedPreferences.Login.Base64.decode(Base64.java:1243) 
    11-12 03:57:06.603: W/System.err(20229): at com.SharedPreferences.Login.Base64.decode(Base64.java:1224) 
    11-12 03:57:06.603: W/System.err(20229): at com.SharedPreferences.Login.AccessApp.decrypt(AccessApp.java:137) 
    11-12 03:57:06.603: W/System.err(20229): at com.SharedPreferences.Login.AccessApp.onClick(AccessApp.java:55) 
    11-12 03:57:06.603: W/System.err(20229): at android.view.View.performClick(View.java:3511) 
    11-12 03:57:06.613: W/System.err(20229): at android.view.View$PerformClick.run(View.java:14105) 
    11-12 03:57:06.635: W/System.err(20229): at android.os.Handler.handleCallback(Handler.java:605) 
    11-12 03:57:06.643: W/System.err(20229): at android.os.Handler.dispatchMessage(Handler.java:92) 
    11-12 03:57:06.669: W/System.err(20229): at android.os.Looper.loop(Looper.java:137) 
    11-12 03:57:06.673: W/System.err(20229): at android.app.ActivityThread.main(ActivityThread.java:4424) 
    11-12 03:57:06.673: W/System.err(20229): at java.lang.reflect.Method.invokeNative(Native Method) 
    11-12 03:57:06.673: W/System.err(20229): at java.lang.reflect.Method.invoke(Method.java:511) 
    11-12 03:57:06.695: W/System.err(20229): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
    11-12 03:57:06.695: W/System.err(20229): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
    11-12 03:57:06.695: W/System.err(20229): at dalvik.system.NativeStart.main(Native Method) 

類檢索保存的字符串和解密：

public void onClick(View arg0) { 

    sp=this.getSharedPreferences("AccessApp", MODE_WORLD_READABLE); 

    byte[] key = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5 }; 

    try { 
     String decryptedUser = decrypt(user, key); 
     user = sp.getString("USERNAME_KEY", decryptedUser); 
    } 
catch (Exception e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
} 
try { 
     String decryptedPass = decrypt(pass, key); 
     pass = sp.getString("PASSWORD_KEY", decryptedPass); 

} catch (Exception e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
} 

    if(lBttn.equals(arg0)){ 

     if((uname.getText().toString().equals(user))&& 
     (pword.getText().toString().equals(pass))) 

      { 
      Toast.makeText(this, "You are Logged In", 20000).show(); 

       Intent intent; 
       intent=new Intent(this,details.class); 
       startActivity(intent); 
       flag=1; 
      } 

     else 
      { 
      Toast.makeText(this, "Wrong Username or Password",20000).show(); 
      flag=0; 
      }  
     } 
     else if(cBttn==arg0){ 
      AlertDialog.Builder builder=new AlertDialog.Builder(this); 
      builder.setTitle("Exit"); 
     builder.setMessage("Do you want to exit"); 
    builder.setCancelable(false); 
    builder.setPositiveButton("Yes",new DialogInterface.OnClickListener() { 

    public void onClick(DialogInterface dialog, int which) { 
    // TODO Auto-generated method stub 
Intent intent = new Intent(Intent.ACTION_MAIN); 
intent.addCategory(Intent.CATEGORY_HOME); 
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
startActivity(intent); 

    finish(); 
    } 
    }); 
    builder.setNegativeButton("No", new DialogInterface.OnClickListener() { 

      public void onClick(DialogInterface arg0, int arg1) { 
       arg0.cancel(); 
      } 
     }); 
    AlertDialog alert=builder.create(); 
    alert.show(); 

     } 

    } 
@Override 
public boolean onKeyDown(int keyCode, KeyEvent event) { 
if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) { 

    Intent intent = new Intent(Intent.ACTION_MAIN); 
     intent.addCategory(Intent.CATEGORY_HOME); 
     intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
     startActivity(intent); 
    finish(); 
} 
return super.onKeyDown(keyCode, event); 
} 

public static String decrypt(String encryptedText, byte[ ] key) throws Exception { 
    SecretKeySpec skeySpec = new SecretKeySpec(key, "AES"); 
    Cipher cipher = Cipher.getInstance("AES"); 
    cipher.init(Cipher.DECRYPT_MODE, skeySpec); 
    byte[] toDecrypt = Base64.decode(encryptedText); 
    byte[] encrypted = cipher.doFinal(toDecrypt); 
    return new String(encrypted); 
} 
} 

聲明：

public class AccessApp extends Activity implements OnClickListener { 
private SharedPreferences sp; 
String user,pass; 
Button lBttn,cBttn; 
EditText uname,pword; 
Intent i; 
int flag=0; 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    lBttn=(Button)findViewById(R.id.login_button); 
    cBttn=(Button)findViewById(R.id.cancel_button); 
    uname=(EditText)findViewById(R.id.username); 
    pword=(EditText)findViewById(R.id.password); 

    lBttn.setOnClickListener(this); 
    cBttn.setOnClickListener(this); 
} 

Answer 1

對不起。我正在改變我的答案。我之前所說的完全錯誤。
原因你所得到的錯誤

java.lang.NullPointerException: Input string was null.

是因爲你已經聲明

String user; 

你還沒有初始化它，你是在功能decrypt調用

String decryptedUser = decrypt(user, key); 

現在用戶爲空。