java 8 对JSONArray 按指定字段排序，升序和倒序，经典

java 8 对JSONArray 按指定字段排序，升序和倒序，经典

以前在内存中用大数据量的排序不论使用冒泡排序还是使用Collections.sort效率都相当低下，现如今Java 8 出现了Comparator 首先这并不是一个方法，而是一个接口

@FunctionalInterface
public interface Comparator<T> {
}

在此不过多阐述它实现的原理，只在这里介绍它的两个实现方法

/**
     * Accepts a function that extracts a {@link java.lang.Comparable
     * Comparable} sort key from a type {@code T}, and returns a {@code
     * Comparator} that compares by that sort key.
     *
     * 
The returned comparator is serializable if the specified function
     * is also serializable.
     *
     * @apiNote
     * For example, to obtain a {@code Comparator} that compares {@code
     * Person} objects by their last name,
     *
     * 
{@code
     *     Comparator byLastName = Comparator.comparing(Person::getLastName);
     * }
     *
     * @param   the type of element to be compared
     * @param   the type of the {@code Comparable} sort key
     * @param  keyExtractor the function used to extract the {@link
     *         Comparable} sort key
     * @return a comparator that compares by an extracted key
     * @throws NullPointerException if the argument is null
     * @since 1.8
     */
    public static <T, U extends Comparable<? super U>> Comparator<T> comparing(
            Function<? super T, ? extends U> keyExtractor)
    {
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)
            (c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
    }

/**
     * Returns a comparator that imposes the reverse ordering of this
     * comparator.
     *
     * @return a comparator that imposes the reverse ordering of this
     *         comparator.
     * @since 1.8
     */
    default Comparator<T> reversed() {
        return Collections.reverseOrder(this);
    }

一、comparing 方法的使用

从注释信息不难看出 comparing 方法 传入一个函数，这个函数携带一个参数，参数类型为List对象或者JSONArray对象
例子：

//json 字符串
String dd = "[{id:1,adress:上海,age:21},{id:2,adress:上海,age:32},{id:3,adress:上海,age:28},{id:4,adress:上海,age:27}]";
//字符串转对象
JSONArray listObjectFifth = JSONObject.parseArray(dd);
//根据age升序排序
listObjectFifth.sort(Comparator.comparing(obj -> ((JSONObject) obj).getBigDecimal("age")));

二、reversed 方法的使用

从注释信息不难看出 reversed 方法返回一个比较器，而且是强制执行此逆序
例子：

//json 字符串
String dd = "[{id:1,adress:上海,age:21},{id:2,adress:上海,age:32},{id:3,adress:上海,age:28},{id:4,adress:上海,age:27}]";
//字符串转对象
JSONArray listObjectFifth = JSONObject.parseArray(dd);
//根据age降序排序
listObjectFifth.sort(Comparator.comparing(obj -> ((JSONObject) obj).getBigDecimal("age")).reversed());

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