利用Apache的commons-beanutils和commons-collections包实现Java对象的按属性排序

在日常工作中经常用到需要对java对象集合或者Map集合中的某个属性做排序，这个需求可以利用Apache的commons-beanutils和commons-collections包来实现，主要实现方式如下：

    public static <T> void sort(List<T> list, String property, boolean asc) {
        Comparator<?> comparator = ComparableComparator.getInstance();
        comparator = ComparatorUtils.nullLowComparator(comparator);
        if (!asc) {
            comparator = ComparatorUtils.reversedComparator(comparator);
        }
        Collections.sort(list, new BeanComparator(property, comparator));
    }

下面看看一个具体实现例子，其中有按对象属性排序和Map某个key排序

首先是一个Java对象

package my.commonsstudy.beanutils;

public class User {
    private String username;
    private String password;
    private String email;
    public User(String username, String password, String email) {
        this.username = username;
        this.password = password;
        this.email = email;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    @Override
    public String toString() {
        return this.username + ", " + this.password + ", " + this.email;
    }
}

排序测试类

package my.commonsstudy.beanutils;

import org.apache.commons.beanutils.BeanComparator;
import org.apache.commons.collections.ComparatorUtils;
import org.apache.commons.collections.comparators.ComparableComparator;

import java.util.*;

public class ComparatorTest {

    public static void main(String[] args) throws Exception {
        test1();
        test2();
    }

    private static void test1() {
        List<Map<String, Object>> users = new ArrayList<Map<String, Object>>();
        for (int i = 0; i < 5; i++) {
            Map<String, Object> user = new LinkedHashMap<String, Object>();
            user.put("username", "user_" + i);
            user.put("password", "passwd_" + i);
            user.put("email", "user_" + i + "@localhost");
            users.add(user);
        }
        System.out.println(users);

        sort(users, "username", false);
        System.out.println(users);

        sort(users, "username", true);
        System.out.println(users);
    }

    private static void test2() {
        List<User> users = new ArrayList<User>();
        for (int i = 0; i < 5; i++) {
            users.add(new User("user_" + i, "passwd_" + i, "user_" + i + "@localhost"));
        }
        System.out.println(users);

        sort(users, "username", false);
        System.out.println(users);

        sort(users, "username", true);
        System.out.println(users);
    }

    public static <T> void sort(List<T> list, String property, boolean asc) {
        Comparator<?> comparator = ComparableComparator.getInstance();
        comparator = ComparatorUtils.nullLowComparator(comparator);
        if (!asc) {
            comparator = ComparatorUtils.reversedComparator(comparator);
        }
        Collections.sort(list, new BeanComparator(property, comparator));
    }
}