import com.alibaba.fastjson.JSON;
import org.springframework.beans.BeanUtils;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
/**
* @author
* @date 2019-12-30 17:47
* @description
*/
public class TestMain {
public static void main(String[] args) {
List<User> list = new ArrayList<>();
User user1 = new User();
user1.setUserId("11111");
user1.setUserName("張三");
user1.setAmount(BigDecimal.valueOf(1500));
User user2 = new User();
user2.setUserId("11111");
user2.setUserName("張三");
user2.setAmount(BigDecimal.valueOf(200));
User user3 = new User();
user3.setUserId("22222");
user3.setUserName("李四");
user3.setAmount(BigDecimal.valueOf(2000));
list.add(user1);
list.add(user2);
list.add(user3);
List<User> data = merged(list);
// 根據用戶ID升序排序,從小到大
data = data.stream().sorted(Comparator.comparing(User::getUserId)).collect(Collectors.toList());
// 根據用戶ID降序排序,從大到小
data = data.stream().sorted(Comparator.comparing(User::getUserId).reversed()).collect(Collectors.toList());
System.out.println(JSON.toJSONString(data));
}
/**
* 根據用戶ID、用戶名對集合中的數據去重,並且合併金額的值
* @param list
* @return
*/
private static List<User> merged(List<User> list) {
List<User> data = new ArrayList<>();
// Collectors.groupingBy根據指定字符串分組排序,由於需要根據多個屬性,先把多個屬性拼接成一個字符串
Map<String, List<User>> collect = list.stream().collect(Collectors.groupingBy(e -> fetchGroupKey(e)));
for (Map.Entry<String, List<User>> entry : collect.entrySet()) {
User user = new User();
// 使用BeanUtils進行重新賦值到新的對象當中,因爲合併,所以只需要保留分組後的一個對象的值
BeanUtils.copyProperties(entry.getValue().get(0), user);
// 由於需要返回一個新的值所以使用map而不是使用forEach,對集合當中的對象某一個屬性的值進行相加
BigDecimal total = entry.getValue().stream().map(User::getAmount).reduce(BigDecimal.ZERO, BigDecimal::add);
user.setAmount(total);
data.add(user);
}
return data;
}
/**
* 根據多個屬性拼接成一個字符串
* @param user
* @return
*/
private static String fetchGroupKey(User user) {
return user.getUserId() + user.getUserName();
}
}
運行輸出
[{"amount":2000,"userId":"22222","userName":"李四"},{"amount":1700,"userId":"11111","userName":"張三"}]
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.stream.Collectors;
/**
* @author
* @date 2019-12-30 17:47
* @description
*/
public class SortUtils {
/**
* 對map的key進行排序
* @param map
* @return
*/
public static Map<String, String> sortMapKey(Map<String,String> map) {
Map<String, String> result = map.entrySet().stream()
.sorted(Map.Entry.comparingByKey())
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
(oleValue, newValue) -> oleValue, LinkedHashMap::new));
return result;
}
/**
* 對map的value進行排序
* @param map
* @return
*/
public static Map<String,String> sortMapValue(Map<String,String> map){
Map<String, String> result = map.entrySet().stream()
.sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
(oldValue, newValue) -> oldValue, LinkedHashMap::new));
return result;
}
}