java List Collections.sort 排序 支持 对象属性 普通数据类型 升序 降序 正序 倒序 排列
import java.lang.reflect.Method;??
import java.text.SimpleDateFormat;??
import java.util.*;??
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public class ListComparator implements Comparator {??
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??? public ListComparator() {}??
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??? public ListComparator(String methodName) {??
??????? this.methodName = methodName;??
??? }??
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??? //空:普通的数据类型 非空:对象数据类型 取methodName返回值比较??
??? String methodName;??
??????
??? public Object getValue(Object bean, String methodName) throws Exception {??
??????? Method getMethod = bean.getClass().getMethod(methodName, null);??
??????? return getMethod.invoke(bean, null);??
??? }??
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??? public int compare(Object obj1, Object obj2) {??
??????? int val = -1;??
??????? try {??
??????????? if ( methodName == null ) {??
??????????????? val = _compare(obj1, obj2);??
??????????? } else {??
??????????????? val = _compare(getValue(obj1, methodName), getValue(obj2, methodName));??
??????????? }??
??????? } catch (Exception ex) {ex.printStackTrace();}??
??????? return val;??
??? }??
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??? public int _compare(Object obj1, Object obj2) throws Exception {??
??????? if ( obj1 == null || obj2 == null ) return obj1 == null ? -1 : 1;??
??????? Class cl = obj1.getClass();??
??????? if ( obj1 instanceof java.lang.Comparable ) {??
??????? //byte int long float..number, date , boolean , char??
??????????? Method getMethod = obj1.getClass().getMethod("compareTo", new Class[]{cl});??
??????????? return (Integer) getMethod.invoke(obj1, new Object[]{obj2});??
??????? }??
??????? return -1;??
??? }??
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}??
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//测试类??
class Test {??
??? Long id;??
??? public Long getId() {??
??????? return id;??
??? }??
??? public void setId(Long id) {??
??????? this.id = id;??
??? }??
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??? public static void main(String[] args) {??
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??????? //普通数据类型? 升序??
??????? SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");??
??????? List list = new ArrayList();??
??????? for (long i = 0; i < 5; i++) {??
??????????? list.add( new Date(System.currentTimeMillis() + (int) (Math.random() *
1000000000)) );??
??????? }??
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??????? ListComparator c = new ListComparator();??
??????? Collections.sort(list, c);??
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??????? for (int i = 0; i < list.size(); i++) {??
??????????? System.out.println(simpleDateFormat.format(list.get(i)));??
??????? }??
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???????? //对象数据类型 降序??
??????? List<Test> userList = new ArrayList();??
??????? Test test = new Test();??
??????? test.setId(null);??
??????? userList.add(test);??
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??????? for (long i = 0; i < 5; i++) {??
??????????? test = new Test();??
??????????? test.setId(i);??
??????????? userList.add(test);??
??????? }??
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??????? c = new ListComparator("getId");??
??????? Collections.sort(userList,Collections.reverseOrder(c));??
??????????
??????? for (int i = 0; i < userList.size(); i++) {??
??????????? System.out.println(userList.get(i).getId());??
??????? }??
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??? }??
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}?
