sort 根据实体类中指定的列名对List中的对象进行排序
在list中经常需要对其中的对象进行排序，有时候排序的需求不一样，根据不同的字段进行排序。
这就使用到了比较器 comparator
不废话，上代码:
下面是3个代码文件。
第一个是实体类，书籍:
package userSort;
public class Book {
private Long id;//书本编号
private String name;//书本名称
private double price;//书本价格
private String author;//作者
private Integer weight;//权重
public Book(Long Id,String Name,double Price,String Author,Integer Weight) {
this.id=Id;
this.name=Name;
this.price=Price;
this.author=Author;
this.weight=Weight;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public Integer getWeight() {
return weight;
}
public void setWeight(Integer weight) {
this.weight = weight;
}
}
第二个代码文件就是本次的重点了，比较器：实现对任何指定的列名进行排序
package userSort;
import java.lang.reflect.Method;
import java.util.Comparator;
/**
* 此文件是根据输入的参数进行排序
* eg： 输入参数为 (String propertyName ,boolean isASC) 返回的结果为 list, 不过是根据propertyName升序排列后的结果
* 根据Student类中的propertyName字段进行排序。
* T表示是Student类，propertyName是类中的一个字段名称
*
* @author YinLinFei
* @param
*/
/**
* 字段名的首字母需要大写
* @author YinLinFei
*
*/
public class sortList implements Comparator {
private String propertyName;
private boolean isAsc;
public sortList(String propertyname, boolean isasc) {
this.propertyName = propertyname;
this.isAsc = isasc;
}
/**
* 需要的是：根据类中的字段对对象进行排序
*
* @return
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
@Override
public int compare(T b1, T b2) {
Class clz = b1.getClass();
Method mth = getPropertyMethod(clz, propertyName);
try {
Object o1 = mth.invoke(b1);
Object o2 = mth.invoke(b2);
if (o1 == null || o2 == null) return 0;
Comparable value1 = (Comparable) o1;
Comparable value2 = (Comparable) o2;
if (isAsc) {
return value1.compareTo(value2);
} else {
return value2.compareTo(value1);
}
} catch (Exception e) {
e.printStackTrace();
}
return 0;
//原先的固定的根据某一个固定的字段进行排序
// if (b1 == null || b2 == null) {
// return 0;
// }
// if (isAsc) {
// return b1.getWeight().compareTo(b2.getWeight());
// } else {
// return b2.getWeight().compareTo(b1.getWeight());
// }
}
// 获取类名
@SuppressWarnings({ "unchecked", "rawtypes" })
public static Method getPropertyMethod(Class clz, String propertyName) {
Method mth = null;
try {
mth = clz.getMethod("get" + propertyName);
} catch (Exception e) {
System.out.println("获取类名发生错误！");
}
return mth;
}
public String getPropertyName() {
return propertyName;
}
public void setPropertyName(String propertyName) {
this.propertyName = propertyName;
}
public boolean isAsc() {
return isAsc;
}
public void setAsc(boolean isAsc) {
this.isAsc = isAsc;
}
}
最后一个是测试文件：
package userSort;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class Main {
public static List getBookList() {
List books = new ArrayList();
Book book1 = new Book(1L, "first", 10.00, "zhangsan", 19);
Book book2 = new Book(2L, "first", 9.00, "zhangsan", 24);
Book book3 = new Book(3L, "first", 8.00, "zhangsan", 29);
Book book4 = new Book(4L, "first", 7.00, "zhangsan", 13);
Book book5 = new Book(5L, "first", 6.00, "zhangsan", 14);
books.add(book1);
books.add(book2);
books.add(book3);
books.add(book4);
books.add(book5);
return books;
}
/**
* 打印函数
*
* @param lisbk
*/
public static void printf(List lisbk) {
if (lisbk.isEmpty() || lisbk == null) {
System.out.println("没有数据");
return;
}
for (Book book : lisbk) {
System.out.println("Id: " + book.getId() + " price: " + book.getPrice() + " weight:" + book.getWeight());
}
System.out.println();
return;
}
public static void main(String[] args) {
List bks = getBookList();
System.out.println("原先的顺序：");
printf(bks);
System.out.println("根据价格排序：");
Collections.sort(bks, new sortList("Price",true));
printf(bks);
System.out.println("根据Id排序：");
Collections.sort(bks, new sortList("Id",true));
printf(bks);
System.out.println("根据weight排序：");
Collections.sort(bks, new sortList("Weight",true));
printf(bks);
}
}
打印结果：
Id: 1 price: 10.0 weight:19
Id: 2 price: 9.0 weight:24
Id: 3 price: 8.0 weight:29
Id: 4 price: 7.0 weight:13
Id: 5 price: 6.0 weight:14
根据价格排序：
Id: 5 price: 6.0 weight:14
Id: 4 price: 7.0 weight:13
Id: 3 price: 8.0 weight:29
Id: 2 price: 9.0 weight:24
Id: 1 price: 10.0 weight:19
根据Id排序：
Id: 1 price: 10.0 weight:19
Id: 2 price: 9.0 weight:24
Id: 3 price: 8.0 weight:29
Id: 4 price: 7.0 weight:13
Id: 5 price: 6.0 weight:14
根据weight排序：
Id: 4 price: 7.0 weight:13
Id: 5 price: 6.0 weight:14
Id: 1 price: 10.0 weight:19
Id: 2 price: 9.0 weight:24
Id: 3 price: 8.0 weight:29