最近在做一個大的項目，其中有一個通過List里面對象的屬性值來去重List，并把相同屬性的其他屬性相加，都說通過Map的key唯一，來去重。記錄一下

首先有一個實體類User

package com.fmj.test;public class User {private String id;private String name;private String password;private int age;private int jine;private String desc;public int getAge() {return age;}public void setAge(int age) {this.age = age;}public int getJine() {return jine;}public void setJine(int jine) {this.jine = jine;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getDesc() {return desc;}public void setDesc(String desc) {this.desc = desc;}public User(String id, String name, String password, int age, int jine, String desc) {this.jine = jine;this.age = age;this.password = password;this.id = id;this.name = name;this.desc = desc;}public User(String id, String name) {this.id = id;this.name = name;}public User() {}@Overridepublic String toString() {return "User [id=" + id + ", name=" + name + ", password=" + password + ", age=" + age + ", jine=" + jine+ ", desc=" + desc + "]";}}

我們想?通過?id?和name來去重，并把age?和jine?相加起來

private static void sub() {List<User> userList = new ArrayList<User>();User u1 = new User("1", "zhangyi", "zhangyipwd", 21, 101, "yiban1");User u2 = new User("2", "zhanger", "zhangerpwd", 22, 102, "yiban2");User u3 = new User("1", "zhangyi", "zhangyipwd", 23, 103, "yiban3");User u4 = new User("4", "zhansi", "zhangsipwd", 24, 104, "yiban4");User u5 = new User("5", "zhangwu", "zhangwupwd", 25, 105, "yiban5");User u6 = new User("6", "zhangliu", "zhangliupwd", 26, 106, "yiban6");userList.add(u1);userList.add(u2);userList.add(u3);userList.add(u4);userList.add(u5);userList.add(u6);List<User> newuserList = new ArrayList<User>();userList.parallelStream().collect(Collectors.groupingBy(o -> (o.getId() + o.getName()), Collectors.toList())).forEach((id, transfer) -> {transfer.stream().reduce((a, b) -> new User(a.getId(), a.getName(), a.getPassword(), a.getAge() + b.getAge(), a.getJine() + b.getJine(), a.getDesc())).ifPresent(newuserList:: add);});System.out.println("處理過的List:--");newuserList.forEach(item->{System.out.println(item.toString());});}

我上面的例子，可以看出u1?和?u3?會被合并，變成一條，運行結果如下

處理過的List:-- User [id=2, name=zhanger, password=zhangerpwd, age=22, jine=102, desc=yiban2] User [id=6, name=zhangliu, password=zhangliupwd, age=26, jine=106, desc=yiban6] User [id=5, name=zhangwu, password=zhangwupwd, age=25, jine=105, desc=yiban5] User [id=4, name=zhansi, password=zhangsipwd, age=24, jine=104, desc=yiban4] User [id=1, name=zhangyi, password=zhangyipwd, age=44, jine=204, desc=yiban3]

這就實現了去重累加，這里我復制了，https://www.cnblogs.com/edda/p/14191917.html，這個文章，對這個tream?確實，小有難度

還記得我上面說過的用Map來處理嗎？下面這個例子會容易理解一點

public static List<User> sub1(List<User> list) {Map<String, User> map = new HashMap<String, User>();list.stream().forEach(user -> {User last = map.get(user.getId()+user.getName());if(map.containsKey(user.getId()+user.getName())){user.setAge(user.getAge() + last.getAge());user.setJine(user.getJine() + last.getJine());map.put(user.getId()+user.getName(), user );}else{map.put(user.getId()+user.getName(), user);}});return map.values().stream().collect(Collectors.toList());}

使用

private static void sub() {List<User> userList = new ArrayList<User>();User u1 = new User("1", "zhangyi", "zhangyipwd", 21, 101, "yiban1");User u2 = new User("2", "zhanger", "zhangerpwd", 22, 102, "yiban2");User u3 = new User("1", "zhangyi", "zhangyipwd", 23, 103, "yiban3");User u4 = new User("4", "zhansi", "zhangsipwd", 24, 104, "yiban4");User u5 = new User("5", "zhangwu", "zhangwupwd", 25, 105, "yiban5");User u6 = new User("6", "zhangliu", "zhangliupwd", 26, 106, "yiban6");userList.add(u1);userList.add(u2);userList.add(u3);userList.add(u4);userList.add(u5);userList.add(u6);List<User> newuserList1 = sub1(userList);System.out.println("處理過的List:--");newuserList1.forEach(item->{System.out.println(item.toString());});}

結果如下：

處理過的List:-- User [id=2, name=zhanger, password=zhangerpwd, age=22, jine=102, desc=yiban2] User [id=6, name=zhangliu, password=zhangliupwd, age=26, jine=106, desc=yiban6] User [id=5, name=zhangwu, password=zhangwupwd, age=25, jine=105, desc=yiban5] User [id=1, name=zhangyi, password=zhangyipwd, age=44, jine=204, desc=yiban3] User [id=4, name=zhansi, password=zhangsipwd, age=24, jine=104, desc=yiban4]

加上?這一句?排序

Collections.sort(newuserList1, (o1, o2)-> Integer.parseInt(o1.getId()) - Integer.parseInt(o2.getId()));

結果如下

處理過的List:-- User [id=1, name=zhangyi, password=zhangyipwd, age=44, jine=204, desc=yiban3] User [id=2, name=zhanger, password=zhangerpwd, age=22, jine=102, desc=yiban2] User [id=4, name=zhansi, password=zhangsipwd, age=24, jine=104, desc=yiban4] User [id=5, name=zhangwu, password=zhangwupwd, age=25, jine=105, desc=yiban5] User [id=6, name=zhangliu, password=zhangliupwd, age=26, jine=106, desc=yiban6]

總結

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