/**
 * 建議使用RandomUtil類創(chuàng)建RandomMeta對象
 * @author wxf on 14-5-5.
 */ 
public class WeightMeta<T> { 
    private final Random ran = new Random(); 
    private final T[] nodes; 
    private final int[] weights; 
    private final int maxW; 
 
    public WeightMeta(T[] nodes, int[] weights) { 
        this.nodes = nodes; 
        this.weights = weights; 
        this.maxW = weights[weights.length - 1]; 
    } 
 
    /**
     * 該方法返回權重隨機對象
     * @return
     */ 
    public T random() { 
        int index = Arrays.binarySearch(weights, ran.nextInt(maxW) + 1); 
        if (index < 0) { 
            index = -1 - index; 
        } 
        return nodes[index]; 
    } 
 
    public T random(int ranInt) { 
        if (ranInt > maxW) { 
            ranInt = maxW; 
        } else if(ranInt < 0){ 
            ranInt = 1; 
        } else { 
            ranInt ++; 
        } 
        int index = Arrays.binarySearch(weights, ranInt); 
        if (index < 0) { 
            index = -1 - index; 
        } 
        return nodes[index]; 
    } 
 
    @Override 
    public String toString() { 
        StringBuilder l1 = new StringBuilder(); 
        StringBuilder l2 = new StringBuilder("[random]\t"); 
        StringBuilder l3 = new StringBuilder("[node]\t\t"); 
        l1.append(this.getClass().getName()).append(":").append(this.hashCode()).append(":\n").append("[index]\t\t"); 
        for (int i = 0; i < weights.length; i++) { 
            l1.append(i).append("\t"); 
            l2.append(weights[i]).append("\t"); 
            l3.append(nodes[i]).append("\t"); 
        } 
        l1.append("\n"); 
        l2.append("\n"); 
        l3.append("\n"); 
        return l1.append(l2).append(l3).toString(); 
    } 
}

/**
 * 隨機工具類
 *
 * 使用權重的集合Map構建隨機元數(shù)據(jù)對象
 *
 * 比如：
 * 我們有3個url地址，他們的權重分別為1,2,3現(xiàn)在我們利用RandomUtil來根據(jù)權重隨機獲取url：
 *
 * <p><blockquote><pre>
 *
 * map.put(url1, 1);
 * map.put(url2, 2);
 * map.put(url3, 3);
 * RandomMeta<String, Integer> md = RandomUtil.buildWeightMeta(map);
 * String weightRandomUrl = md.random();
 *
 * </pre></blockquote><p>
 *
 * @author wxf on 14-5-5.
 */ 
public class RandomUtil { 
    public static <T> WeightMeta<T> buildWeightMeta(final Map<T, Integer> weightMap) { 
        final int size = weightMap.size(); 
        Object[] nodes = new Object[size]; 
        int[] weights = new int[size]; 
        int index = 0; 
        int weightAdder = 0; 
        for (Map.Entry<T, Integer> each : weightMap.entrySet()) { 
            nodes[index] = each.getKey(); 
            weights[index++] = (weightAdder = weightAdder + each.getValue()); 
        } 
        return new WeightMeta<T>((T[]) nodes, weights); 
    } 
}