List根据对象中的指定元素进行排序
背景: 在实际开发中,产品对数据会有个各种要求,排序应该最常见,也是比较麻烦的一件事情,很多时候数据不是一条SQL查询出来的,我们将其封装在List中,那么问题来了,怎么才能实现产品的变态要求呢?接下来就是见证奇迹了!
排序功能
代码如下（示例）：
import java.lang.reflect.Field;
import java.text.NumberFormat;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.List;
/**
* @author xzx
* 在数据库中查出来的列表中，往往需要对不同的字段重新排序。 一般的做法都是使用排序的字段，重新到数据库中查询。
* 如果不到数据库查询，直接在第一次查出来的list中排序，无疑会提高系统的性能。 下面就写一个通用的方法，对list排序，
*
* 至少需要满足以下5点：
*
* ①.list元素对象类型任意
* ---->使用泛型解决
*
* ②.可以按照list元素对象的任意多个属性进行排序,即可以同时指定多个属性进行排序
* --->使用java的可变参数解决
*
* ③.list元素对象属性的类型可以是数字(byte、short、int、long、float、double等，包括正数、负数、0)、字符串(char、String)、日期(java.util.Date)
* --->对于数字：统一转换为固定长度的字符串解决,比如数字3和123，转换为"003"和"123" ;再比如"-15"和"7"转换为"-015"和"007"
* --->对于日期：可以先把日期转化为long类型的数字，数字的解决方法如上
*
* ④.list元素对象的属性可以没有相应的getter和setter方法
* --->可以使用java反射进行获取private和protected修饰的属性值
*
* ⑤.list元素对象的对象的每个属性都可以指定是升序还是降序
* -->使用2个重写的方法(一个方法满足所有属性都按照升序(降序)，另外一个方法满足每个属性都能指定是升序(降序))
*
*
*/
public class ListUtilsMain {
/**
* 对list的元素按照多个属性名称排序,
* list元素的属性可以是数字（byte、short、int、long、float、double等，支持正数、负数、0）、char、String、java.util.Date
*
*
* @param lsit
* @param sortname
* list元素的属性名称
* @param isAsc
* true升序，false降序
*/
public static <E> void sort(List<E> list, final boolean isAsc, final String... sortnameArr) {
Collections.sort(list, new Comparator<E>() {
public int compare(E a, E b) {
int ret = 0;
try {
for (int i = 0; i < sortnameArr.length; i++) {
ret = ListUtilsMain.compareObject(sortnameArr[i], isAsc, a, b);
if (0 != ret) {
break;
}
}
} catch (Exception e) {
e.printStackTrace();
}
return ret;
}
});
}
/**
* 给list的每个属性都指定是升序还是降序
*
* @param list
* @param sortnameArr 参数数组
* @param typeArr 每个属性对应的升降序数组， true升序，false降序
*/
public static <E> void sort(List<E> list, final String[] sortnameArr, final boolean[] typeArr) {
if (sortnameArr.length != typeArr.length) {
throw new RuntimeException("属性数组元素个数和升降序数组元素个数不相等");
}
Collections.sort(list, new Comparator<E>() {
public int compare(E a, E b) {
int ret = 0;
try {
for (int i = 0; i < sortnameArr.length; i++) {
ret = ListUtilsMain.compareObject(sortnameArr[i], typeArr[i], a, b);
if (0 != ret) {
break;
}
}
} catch (Exception e) {
e.printStackTrace();
}
return ret;
}
});
}
/**
* 对2个对象按照指定属性名称进行排序
*
* @param sortname
* 属性名称
* @param isAsc
* true升序，false降序
* @param a
* @param b
* @return
* @throws Exception
*/
private static <E> int compareObject(final String sortname, final boolean isAsc, E a, E b) throws Exception {
int ret;
Object value1 = ListUtilsMain.forceGetFieldValue(a, sortname);
Object value2 = ListUtilsMain.forceGetFieldValue(b, sortname);
String str1 = value1.toString();
String str2 = value2.toString();
if (value1 instanceof Number && value2 instanceof Number) {
int maxlen = Math.max(str1.length(), str2.length());
str1 = ListUtilsMain.addZero2Str((Number) value1, maxlen);
str2 = ListUtilsMain.addZero2Str((Number) value2, maxlen);
} else if (value1 instanceof Date && value2 instanceof Date) {
long time1 = ((Date) value1).getTime();
long time2 = ((Date) value2).getTime();
int maxlen = Long.toString(Math.max(time1, time2)).length();
str1 = ListUtilsMain.addZero2Str(time1, maxlen);
str2 = ListUtilsMain.addZero2Str(time2, maxlen);
}
if (isAsc) {
ret = str1.compareTo(str2);
} else {
ret = str2.compareTo(str1);
}
return ret;
}
/**
* 给数字对象按照指定长度在左侧补0.
*
* 使用案例: addZero2Str(11,4) 返回 "0011", addZero2Str(-18,6)返回 "-000018"
*
* @param numObj
* 数字对象
* @param length
* 指定的长度
* @return
*/
public static String addZero2Str(Number numObj, int length) {
NumberFormat nf = NumberFormat.getInstance();
// 设置是否使用分组
nf.setGroupingUsed(false);
// 设置最大整数位数
nf.setMaximumIntegerDigits(length);
// 设置最小整数位数
nf.setMinimumIntegerDigits(length);
return nf.format(numObj);
}
/**
* 获取指定对象的指定属性值（去除private,protected的限制）
*
* @param obj
* 属性名称所在的对象
* @param fieldName
* 属性名称
* @return
* @throws Exception
*/
public static Object forceGetFieldValue(Object obj, String fieldName) throws Exception {
Field field = obj.getClass().getDeclaredField(fieldName);
Object object = null;
boolean accessible = field.isAccessible();
if (!accessible) {
// 如果是private,protected修饰的属性，需要修改为可以访问的
field.setAccessible(true);
object = field.get(obj);
// 还原private,protected属性的访问性质
field.setAccessible(accessible);
return object;
}
object = field.get(obj);
return object;
}
}
测试类
代码如下（示例）：
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;
public class Test {
public static void main(String[] args) throws Exception {
Test testObj = new Test();
List<UserInfo> list = new ArrayList<UserInfo>();
// public UserInfo(Integer userId, String username, Date birthDate,Integer age, float fRate, char ch)
SimpleDateFormat formater = new SimpleDateFormat("yyyy-MM-dd");
UserInfo user1 = new UserInfo(3, "bbb", formater.parse("1980-12-01"), 1, 1.2f, 'a');
UserInfo user2 = new UserInfo(0, "126", formater.parse("1900-10-11"), 03, -3.6f, 'c');
UserInfo user3 = new UserInfo(12, "5", formater.parse("1973-08-21"), 15, 9.32f, 'f');
UserInfo user4 = new UserInfo(465, "1567", formater.parse("2012-01-26"), 20, 12.56f, '0');
UserInfo user5 = new UserInfo(2006, "&4m", formater.parse("2010-05-08"), 100, 165.32f, '5');
UserInfo user6 = new UserInfo(5487, "hf67", formater.parse("2016-12-30"), 103, 56.32f, 'm');
UserInfo user7 = new UserInfo(5487,"jigg", formater.parse("2000-10-16"), 103, 56.32f, 'm');
UserInfo user8 = new UserInfo(5487, "jigg", formater.parse("1987-07-25"), 103, 56.32f, 'm');
list.add(user1);
list.add(user2);
list.add(user3);
list.add(user4);
list.add(user5);
list.add(user6);
list.add(user7);
list.add(user8);
System.out.println("\n-------原来序列-------------------");
testObj.printfUserInfoList(list);
// 按userId升序、username降序、birthDate升序排序
String [] sortNameArr = {"userId","username","birthDate"};
boolean [] isAscArr = {true,false,true};
ListUtilsMain.sort(list,sortNameArr,isAscArr);
System.out.println("\n--------按按userId升序、username降序、birthDate升序排序（如果userId相同，则按照username降序,如果username相同，则按照birthDate升序）------------------");
testObj.printfUserInfoList(list);
// 按userId、username、birthDate都升序排序
ListUtilsMain.sort(list, true, "userId", "username","birthDate");
System.out.println("\n--------按userId、username、birthDate排序（如果userId相同，则按照username升序,如果username相同，则按照birthDate升序）------------------");
testObj.printfUserInfoList(list);
// 按userId、username都倒序排序
ListUtilsMain.sort(list, false, "userId", "username");
System.out.println("\n--------按userId和username倒序（如果userId相同，则按照username倒序）------------------");
testObj.printfUserInfoList(list);
// 按username、birthDate都升序排序
ListUtilsMain.sort(list, true, "username", "birthDate");
System.out.println("\n---------按username、birthDate升序（如果username相同，则按照birthDate升序）-----------------");
testObj.printfUserInfoList(list);
// 按birthDate倒序排序
ListUtilsMain.sort(list, false, "birthDate");
System.out.println("\n---------按birthDate倒序-----------------");
testObj.printfUserInfoList(list);
// 按fRate升序排序
ListUtilsMain.sort(list, true, "fRate");
System.out.println("\n---------按fRate升序-----------------");
testObj.printfUserInfoList(list);
// 按ch倒序排序
ListUtilsMain.sort(list, false, "ch");
System.out.println("\n---------按ch倒序-----------------");
testObj.printfUserInfoList(list);
}
private void printfUserInfoList(List<UserInfo> list) {
for (UserInfo user : list) {
System.out.println(user.toString());
}
}
}
实体类
package com.smartxp.api.test;
import java.text.SimpleDateFormat;
import java.util.Date;
public class UserInfo {
private static final long serialVersionUID = -3522051445403971732L;
private Integer userId;
private String username;
private Date birthDate;
private Integer age;
private float fRate;
private char ch;
public Date getBirthDate() {
return birthDate;
}
public String getBirthDatestr() {
SimpleDateFormat formater = new SimpleDateFormat("yyyy-MM-dd");
return formater.format(getBirthDate());
}
public UserInfo(Integer userId, String username, Date birthDate, Integer age, float fRate, char ch) {
super();
this.userId = userId;
this.username = username;
this.birthDate = birthDate;
this.age = age;
this.fRate = fRate;
this.ch = ch;
}
@Override
public String toString() {
return "UserInfo [userId=" + userId + ", \tusername=" + username + ", \tbirthDate=" + getBirthDatestr()
+ ", \tage=" + age + ", fRate=" + fRate + ", ch=" + ch + "]";
}
}
运行结果
-------原来序列-------------------
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
--------按按userId升序、username降序、birthDate升序排序（如果userId相同，则按照username降序,如果username相同，则按照birthDate升序）------------------
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
--------按userId、username、birthDate排序（如果userId相同，则按照username升序,如果username相同，则按照birthDate升序）------------------
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
--------按userId和username倒序（如果userId相同，则按照username倒序）------------------
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
---------按username、birthDate升序（如果username相同，则按照birthDate升序）-----------------
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
---------按birthDate倒序-----------------
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
---------按fRate升序-----------------
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
---------按ch倒序-----------------
UserInfo [userId=5487, username=hf67, birthDate=2016-12-30, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=2000-10-16, age=103, fRate=56.32, ch=m]
UserInfo [userId=5487, username=jigg, birthDate=1987-07-25, age=103, fRate=56.32, ch=m]
UserInfo [userId=12, username=5, birthDate=1973-08-21, age=15, fRate=9.32, ch=f]
UserInfo [userId=0, username=126, birthDate=1900-10-11, age=3, fRate=-3.6, ch=c]
UserInfo [userId=3, username=bbb, birthDate=1980-12-01, age=1, fRate=1.2, ch=a]
UserInfo [userId=2006, username=&4m, birthDate=2010-05-08, age=100, fRate=165.32, ch=5]
UserInfo [userId=465, username=1567, birthDate=2012-01-26, age=20, fRate=12.56, ch=0]