import org.springframework.util.CollectionUtils;
import java.lang.reflect.Field;
import java.sql.Date;
import java.text.NumberFormat;
import java.util.*;
import java.util.stream.Collectors;
/**
* @author yaoguanquan
* @creote 2020-08-06-15:36
*/
public class MemoryPagination {
/**
* 给list的每个属性都指定是升序还是降序
* 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 list 数据集合
* @param pageNum 第几页
* @param pageSize 每页多少条
* @param isSort 是否排序
* @param sortNameArr 参数数组
* @param sortArr 每个属性对应的升降序数组， true升序，false降序
*/
public static <E> List<E> sortMemoryPagination(List<E> list, int pageNum, int pageSize,final boolean isSort , final String[] sortNameArr, final boolean[] sortArr) {
if(isSort){
if (sortNameArr.length != sortArr.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 = MemoryPagination.compareObject(sortNameArr[i], sortArr[i], a, b);
if (0 != ret) {
break;
}
}
} catch (Exception e) {
e.printStackTrace();
}
return ret;
}
});
}
return pagination(list,pageNum,pageSize);
}
/**
* 内存分页
*
* @param records 待分页的数据
* @param pageNum 当前页码
* @param pageSize 每页显示的条数
* @return 分页之后的数据
*/
private static <T> List<T> pagination(List<T> records, int pageNum, int pageSize) {
if (CollectionUtils.isEmpty(records)) {
return Collections.emptyList();
}
int totalCount = records.size();
int remainder = totalCount % pageSize;
int pageCount = (remainder > 0) ? totalCount/pageSize + 1 : totalCount/pageSize;
if (remainder == 0) {
return records.stream().skip((pageNum - 1) * pageSize).limit(pageSize).collect(Collectors.toList());
} else {
if (pageNum == pageCount) {
return records.stream().skip((pageNum - 1) * pageSize).limit(totalCount).collect(Collectors.toList());
} else {
return records.stream().skip((pageNum - 1) * pageSize).limit(pageSize).collect(Collectors.toList());
}
}
}
/**
* 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 = MemoryPagination.forceGetFieldValue(a, sortname);
Object value2 = MemoryPagination.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 = MemoryPagination.addZero2Str((Number) value1, maxlen);
str2 = MemoryPagination.addZero2Str((Number) value2, maxlen);
} else if (value1 instanceof java.sql.Date && value2 instanceof java.sql.Date) {
long time1 = ((java.sql.Date) value1).getTime();
long time2 = ((Date) value2).getTime();
int maxlen = Long.toString(Math.max(time1, time2)).length();
str1 = MemoryPagination.addZero2Str(time1, maxlen);
str2 = MemoryPagination.addZero2Str(time2, maxlen);
}
if (isAsc) {
ret = str1.compareTo(str2);
} else {
ret = str2.compareTo(str1);
}
return ret;
}
/**
* 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;
}
/**
* 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);
}
public static void main(String[] args) {
List<SysDict> list = new ArrayList<>();
list.add(new SysDict(1,"test1","1",1,3.32));
list.add(new SysDict(3,"test3","3",3,4.13));
list.add(new SysDict(2,"test2","11",2,4.11));
list.add(new SysDict(4,"test4","4",4,23.23));
list.add(new SysDict(5,"test5","5",5,0.23));
list.add(new SysDict(6,"test6","22",6,0.23));
list.add(new SysDict(7,"test7","3",7,0.23));
list.add(new SysDict(8,"test8","0.2",8,0.23));
String[] sortnameArr = {"ss","sort"};
boolean[] typeArr = {true,false};
List<SysDict> ss = sortMemoryPagination(list, 1, 2, true, sortnameArr,typeArr);
System.out.println(ss.toString());
}
}
//class SysDict {
// private Integer id;
// private String name;
// private String value;
// private Integer sort;
// private Double ss;
//
// public SysDict(Integer id, String name, String value, Integer sort,Double ss) {
// this.id = id;
// this.name = name;
// this.value = value;
// this.sort = sort;
// this.ss = ss;
// }
//
// public Double getSs() {
// return ss;
// }
//
// public void setSs(Double ss) {
// this.ss = ss;
// }
//
// public Integer getId() {
// return id;
// }
//
// public void setId(Integer id) {
// this.id = id;
// }
//
// public String getName() {
// return name;
// }
//
// public void setName(String name) {
// this.name = name;
// }
//
// public String getValue() {
// return value;
// }
//
// public void setValue(String value) {
// this.value = value;
// }
//
// public Integer getSort() {
// return sort;
// }
//
// public void setSort(Integer sort) {
// this.sort = sort;
// }
//
// @Override
// public String toString() {
// return "SysDict{" +
// "id=" + id +
// ", name='" + name + '\'' +
// ", value='" + value + '\'' +
// ", sort=" + sort +
// ", ss=" + ss +
// '}';
// }
//
//}内存分页 二（java8 字段排序）
发布于 2020-08-06 544 次阅读
叨叨几句... NOTHING