java.util.prefs.Preferences.put（）工作，但Preferences.nodeExists（）總是返回false

Question

我有一些簡單的代碼，用於學習使用路標庫進行OAuth身份驗證。我試圖使用java.util.prefs.Preferences將請求令牌，令牌機密和引腳保存爲Java首選項。將數據放入首選項可以正常工作（我檢查文件是否已創建並存儲了信息）。但是，在我將put()的數據立即寫入Preferences文件後，我試着檢查節點是否存在，並且我總是得到false。

我也嘗試過重新運行代碼，然後在嘗試再次保存數據之前檢查節點的存在，但我仍然得到錯誤信息。

我在做什麼不正確？

下面是代碼：

package com.example; 

import java.io.BufferedReader; 
import java.io.InputStreamReader; 
import java.net.HttpURLConnection; 
import java.net.URL; 
import java.util.prefs.Preferences; 

import oauth.signpost.OAuth; 
import oauth.signpost.OAuthConsumer; 
import oauth.signpost.OAuthProvider; 
import oauth.signpost.basic.DefaultOAuthConsumer; 
import oauth.signpost.basic.DefaultOAuthProvider; 

public class ReadMain { 

    public static void main(String[] args) throws Exception { 

     OAuthConsumer consumer = 
     new DefaultOAuthConsumer(
       "??", 
         "??"); 

     OAuthProvider provider = 
     new DefaultOAuthProvider(
      "https://www.readability.com/api/rest/v1/oauth/request_token/", 
        "https://www.readability.com/api/rest/v1/oauth/access_token/", 
        "https://www.readability.com/api/rest/v1/oauth/authorize/"); 

     System.out.println("Fetching request token from Readability..."); 

     Preferences prefs = Preferences.userNodeForPackage(ReadMain.class); 

     final String PREF_TokenSecret = "com/example/TS"; 
     final String PREF_RequestToken = "com/example/RT"; 
     final String PREF_ReadabilityPin = "com/example/RP"; 

     boolean exists = 
      prefs.nodeExists(PREF_TokenSecret) && 
     prefs.nodeExists(PREF_RequestToken) && 
     prefs.nodeExists(PREF_ReadabilityPin); 

     if (prefs.nodeExists(PREF_TokenSecret)) 
     { 
     System.out.println("Token secret exists!"); 
     } 

     if (prefs.nodeExists(PREF_RequestToken)) 
     { 
     System.out.println("Request token exists!"); 
     } 

     if (prefs.nodeExists(PREF_ReadabilityPin)) 
     { 
     System.out.println("Readability pin exists!"); 
     } 

     String pin; 

     if (exists) 
     { 
     consumer.setTokenWithSecret( 
       prefs.get(PREF_RequestToken,""), 
       prefs.get(PREF_TokenSecret,"")); 
      pin = prefs.get(PREF_ReadabilityPin,""); 
     } 
     else 
     { 
     // we do not support callbacks, thus pass OOB 
     String authUrl = provider.retrieveRequestToken(consumer, OAuth.OUT_OF_BAND); 

     System.out.println("Request token: " + consumer.getToken()); 
     System.out.println("Token secret: " + consumer.getTokenSecret()); 

     prefs.put(PREF_RequestToken, consumer.getToken()); 
     prefs.put(PREF_TokenSecret, consumer.getTokenSecret()); 

     System.out.println("Now visit:\n" + authUrl + "\n... and grant this app authorization"); 
     System.out.println("Enter the PIN code and hit ENTER when you're done:"); 

     BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 
     pin = br.readLine(); 

     prefs.put(PREF_ReadabilityPin, pin); 

     if (prefs.nodeExists(PREF_TokenSecret)) 
     { 
      System.out.println("Token secret exists!"); 
     } 

     if (prefs.nodeExists(PREF_RequestToken)) 
     { 
      System.out.println("Request token exists!"); 
     } 

     if (prefs.nodeExists(PREF_ReadabilityPin)) 
     { 
      System.out.println("Readability pin exists!"); 
     } 
     } 

     System.out.println("Fetching access token from Readability..."); 
     provider.retrieveAccessToken(consumer, pin); 

     System.out.println("Access token: " + consumer.getToken()); 
     System.out.println("Token secret: " + consumer.getTokenSecret()); 

     URL url = new URL("https://www.readability.com/api/rest/v1/bookmarks?user=marcusps&archive=1"); 
     HttpURLConnection request = (HttpURLConnection) url.openConnection(); 

     consumer.sign(request); 

     System.out.println("Sending request to Readability..."); 
     request.connect(); 

     System.out.println("Response: " + request.getResponseCode() + " " 
      + request.getResponseMessage()); 
    } 
} 

Answer 1

put(..)的相反操作get(..)。所以：

boolean exists = prefs.get(key, null) != null; 

的get(..)方法，如果有什麼規定項下找到返回第二個參數。

nodeExists()與偏好的層次結構有關，可以在您使用prefs.node(..)創建節點時使用。但是你似乎需要一個扁平的結構，所以你不需要層次結構。