List集合中元素排序

　　  public static final String DESC = "desc"; 
     public static final String ASC = "asc"; 
    
    
    /**
     * 用途:对一个List集合数组进行排序
     * 
     * 说明:
     *         目前可以对List<java.lang.Class>、List<POJO>、List<Map>这三种类型集合进行排序
     * 
     * @param list       排序操作的集合对象
     * @param property  指定集合中元素的排序字段,如果集合元素不是对象类型可以传值为null 
     * @param sort        用于指定是升序还是降序     CollectionsUtil.DESC--降序      CollectionsUtil.ASC--升序
     * @date 2018.04.27 PM
     */
    public static <T> void sortOnList(List<T> list,final Object property,final String sort){
        Collections.sort(list,new Comparator<T>(){
            @Override
            public int compare(T o1, T o2) {
                Integer a1 = null;
                Integer a2 = null;
                if(o1 instanceof Integer) {  //针对List<Integer>
                    a1 = (Integer) o1;
                    a2 = (Integer) o2;
                } else if(o1 instanceof String) { //针对List<String>
                    a1 = Integer.valueOf(o1.toString());
                    a2 = Integer.valueOf(o2.toString());
                } else if(o1 instanceof Map) {   //针对List<Map<String,String>类型
                    Map temp1 = (Map) o1;
                    Map temp2 = (Map) o2;
                    Object object = temp1.get(property);
                    if(object instanceof Integer) { 
                        a1 = (Integer) object;
                        a2 = (Integer) temp2.get(property);
                    } else if(object instanceof String){ //根据Map中value来进行排序String类型需要转换
                        a1 = Integer.parseInt(object.toString());
                        a2 = Integer.parseInt(temp2.get(property).toString());
                    }
                } else  {   //针对对象类型
                    Class c1 = o1.getClass();
                    Class c2 = o2.getClass();
                    try {
                        Field declaredField1 = c1.getDeclaredField(property.toString());
                        Field declaredField2 = c2.getDeclaredField(property.toString());
                        declaredField1.setAccessible(true);  
                        declaredField2.setAccessible(true);  
                        a1 = Integer.parseInt(declaredField1.get(o1).toString());  
                        a2 = Integer.parseInt(declaredField2.get(o2).toString());  
                    } catch (Exception e) {
                        e.printStackTrace();
                    } 
                }
                if(sort.equals(CollectionsUtil.ASC))   //升序
                    return a1.compareTo(a2);
                else                                   //降序
                    return a2.compareTo(a1);
            }
        });
    }

package hello1;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import hello.Student;

public class Main {
    
    public static void main(String[] args) {
        Student s1 = new Student();
        s1.setId(6);
        
        Student s2 = new Student();
        s2.setId(66);
        
        Student s3 = new Student();
        s3.setId(1);
        
        Student s4 = new Student();
        s4.setId(55);
        
        List<Student> list = new ArrayList<>();
        list.add(s1);
        list.add(s2);
        list.add(s3);
        list.add(s4);
        
        System.out.println("未排序结果:"+ list);
        
        
        //根据Student对象id属性排序
        Collections.sort(list, new Comparator<Student>() {

            @Override
            public int compare(Student o1, Student o2) {
                return o1.getId() - o2.getId();
            }
            
        });
        
        System.out.println("排序后结果:"+ list);
        
    }

}