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

Java代码


import java.lang.reflect.Method;
import java.text.SimpleDateFormat;
import java.util.*;

public class ListComparator implements Comparator {

public ListComparator() {}

public ListComparator(String methodName) {
this.methodName = methodName;
}

//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);
}

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;
}

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;
}

}

//测试类
class Test {
Long id;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}

public static void main(String[] args) {

//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)) );
}

ListComparator c = new ListComparator();
Collections.sort(list, c);

for (int i = 0; i < list.size(); i++) {
System.out.println(simpleDateFormat.format(list.get(i)));
}

//对象数据类型 降序
List<Test> userList = new ArrayList();
Test test = new Test();
test.setId(null);
userList.add(test);

for (long i = 0; i < 5; i++) {
test = new Test();
test.setId(i);
userList.add(test);
}

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());
}

}

}