ListResourceBundle.java

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/*
 * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - 1998 - All Rights Reserved
 *
 * The original version of this source code and documentation
 * is copyrighted and owned by Taligent, Inc., a wholly-owned
 * subsidiary of IBM. These materials are provided under terms
 * of a License Agreement between Taligent and Sun. This technology
 * is protected by multiple US and International patents.
 *
 * This notice and attribution to Taligent may not be removed.
 * Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.util;

import sun.util.ResourceBundleEnumeration;

/**
 * <code>ListResourceBundle</code> is an abstract subclass of
 * <code>ResourceBundle</code> that manages resources for a locale
 * in a convenient and easy to use list. See <code>ResourceBundle</code> for
 * more information about resource bundles in general.
 *
 * <P>
 * Subclasses must override <code>getContents</code> and provide an array,
 * where each item in the array is a pair of objects.
 * The first element of each pair is the key, which must be a
 * <code>String</code>, and the second element is the value associated with
 * that key.
 *
 * <p>
 * The following <a id="sample">example</a> shows two members of a resource
 * bundle family with the base name "MyResources".
 * "MyResources" is the default member of the bundle family, and
 * "MyResources_fr" is the French member.
 * These members are based on <code>ListResourceBundle</code>
 * (a related <a href="PropertyResourceBundle.html#sample">example</a> shows
 * how you can add a bundle to this family that's based on a properties file).
 * The keys in this example are of the form "s1" etc. The actual
 * keys are entirely up to your choice, so long as they are the same as
 * the keys you use in your program to retrieve the objects from the bundle.
 * Keys are case-sensitive.
 * <blockquote>
 * <pre>
 *
 * public class MyResources extends ListResourceBundle {
 *     protected Object[][] getContents() {
 *         return new Object[][] {
 *         // LOCALIZE THIS
 *             {"s1", "The disk \"{1}\" contains {0}."},  // MessageFormat pattern
 *             {"s2", "1"},                               // location of {0} in pattern
 *             {"s3", "My Disk"},                         // sample disk name
 *             {"s4", "no files"},                        // first ChoiceFormat choice
 *             {"s5", "one file"},                        // second ChoiceFormat choice
 *             {"s6", "{0,number} files"},                // third ChoiceFormat choice
 *             {"s7", "3 Mar 96"},                        // sample date
 *             {"s8", new Dimension(1,5)}                 // real object, not just string
 *         // END OF MATERIAL TO LOCALIZE
 *         };
 *     }
 * }
 *
 * public class MyResources_fr extends ListResourceBundle {
 *     protected Object[][] getContents() {
 *         return new Object[][] {
 *         // LOCALIZE THIS
 *             {"s1", "Le disque \"{1}\" {0}."},          // MessageFormat pattern
 *             {"s2", "1"},                               // location of {0} in pattern
 *             {"s3", "Mon disque"},                      // sample disk name
 *             {"s4", "ne contient pas de fichiers"},     // first ChoiceFormat choice
 *             {"s5", "contient un fichier"},             // second ChoiceFormat choice
 *             {"s6", "contient {0,number} fichiers"},    // third ChoiceFormat choice
 *             {"s7", "3 mars 1996"},                     // sample date
 *             {"s8", new Dimension(1,3)}                 // real object, not just string
 *         // END OF MATERIAL TO LOCALIZE
 *         };
 *     }
 * }
 * </pre>
 * </blockquote>
 *
 * <p>
 * The implementation of a {@code ListResourceBundle} subclass must be thread-safe
 * if it's simultaneously used by multiple threads. The default implementations
 * of the methods in this class are thread-safe.
 *
 * @see ResourceBundle
 * @see PropertyResourceBundle
 * @since 1.1
 */
// 简化的资源集，属性集硬编码到代码中，子类可以实现为国际化资源，然后从ResourceBundle内加载
public abstract class ListResourceBundle extends ResourceBundle {
    // 属性集
    private volatile Map<String, Object> lookup = null;
    
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    public ListResourceBundle() {
    }
    
    // 由key查找value
    public final Object handleGetObject(String key) {
        // 懒加载，创建属性集
        if(lookup == null) {
            loadLookup();
        }
        
        if(key == null) {
            throw new NullPointerException();
        }
        
        return lookup.get(key); // this class ignores locales
    }
    
    /**
     * Returns an <code>Enumeration</code> of the keys contained in
     * this <code>ResourceBundle</code> and its parent bundles.
     *
     * @return an <code>Enumeration</code> of the keys contained in
     * this <code>ResourceBundle</code> and its parent bundles.
     *
     * @see #keySet()
     */
    // 返回所有key的集合，包括父级资源的key
    public Enumeration<String> getKeys() {
        // lazily load the lookup hashtable.
        if(lookup == null) {
            loadLookup();
        }
        
        ResourceBundle parent = this.parent;
        return new ResourceBundleEnumeration(lookup.keySet(), (parent != null) ? parent.getKeys() : null);
    }
    
    /**
     * Returns an array in which each item is a pair of objects in an
     * <code>Object</code> array. The first element of each pair is
     * the key, which must be a <code>String</code>, and the second
     * element is the value associated with that key.  See the class
     * description for details.
     *
     * @return an array of an <code>Object</code> array representing a
     * key-value pair.
     */
    // 获取硬编码的所有键值对资源（要求key是非空字符串，值非空）
    protected abstract Object[][] getContents();
    
    /**
     * Returns a <code>Set</code> of the keys contained
     * <em>only</em> in this <code>ResourceBundle</code>.
     *
     * @return a <code>Set</code> of the keys contained only in this
     * <code>ResourceBundle</code>
     *
     * @see #keySet()
     * @since 1.6
     */
    // 返回key的集合
    protected Set<String> handleKeySet() {
        if(lookup == null) {
            loadLookup();
        }
        return lookup.keySet();
    }
    
    /**
     * We lazily load the lookup hashtable.  This function does the
     * loading.
     */
    // 创建属性集
    private synchronized void loadLookup() {
        if(lookup != null) {
            return;
        }
        
        Object[][] contents = getContents();
        HashMap<String, Object> temp = new HashMap<>(contents.length);
        for(Object[] content : contents) {
            // key must be non-null String, value must be non-null
            String key = (String) content[0];
            Object value = content[1];
            if(key == null || value == null) {
                throw new NullPointerException();
            }
            temp.put(key, value);
        }
        
        lookup = temp;
    }
}