java.util.prefs.Preferences.put() 有效，但 Preferences.nodeExists() 总是返回 false

Question

我有一些简单的代码，我正在使用它来学习使用路标库的 OAuth 身份验证。我正在尝试使用 java.util.prefs.Preferences 将请求 token 、 token secret 和 pin 保存为 Java 首选项。将数据放入首选项中效果很好(我检查文件是否已创建并存储了信息)。然而，在我将数据 put() 到 Preferences 文件后，我立即尝试检查该节点是否存在，但我总是得到 false。

我也尝试过重新运行代码，并在尝试再次保存数据之前检查节点是否存在，但我仍然得到错误。

我做错了什么？

代码如下:

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(..)的相反操作是get(..)。所以:

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

get(..) 方法在指定键下没有找到任何内容时返回第二个参数。

nodeExists() 与偏好的层次结构相关，可以在您使用 prefs.node(..) 创建节点时使用.但你似乎需要一个平面结构，所以我认为你不需要层次结构。