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Java8 Stream對兩個 List 遍歷匹配數(shù)據(jù)的優(yōu)化處理操作

更新時間：2020年08月17日 09:59:12 作者：yang名揚(yáng)

這篇文章主要介紹了Java8 Stream對兩個 List 遍歷匹配數(shù)據(jù)的優(yōu)化處理操作，具有很好的參考價值，希望對大家有所幫助。一起跟隨小編過來看看吧

使用場景，有兩個List<Map<String,Object>>集合，第一個集合的所有元素都是需要保留的。

第一個集合的值為：

{name=張三豐1, id=1}
{name=張三豐2, id=2}
{name=張三豐3, id=3}
{name=張三豐4, id=4}
{name=張三豐5, id=5}
{name=張三豐6, id=6}
{name=張三豐7, id=7}
{name=張三豐8, id=8}

第二個集合的值為：

{grade=61, id=1}
{grade=62, id=2}
{grade=63, id=3}
{grade=64, id=4}

需要根據(jù)兩個集合中id值相同，就把第二個集合中的grade值賦給第一個集合，如果不匹配，默認(rèn)grade值為0

結(jié)果是這樣：

{grade=61, name=張三豐1, id=1}
{grade=62, name=張三豐2, id=2}
{grade=63, name=張三豐3, id=3}
{grade=64, name=張三豐4, id=4}
{grade=0, name=張三豐5, id=5}
{grade=0, name=張三豐6, id=6}
{grade=0, name=張三豐7, id=7}
{grade=0, name=張三豐8, id=8}

具體實(shí)現(xiàn)代碼：

  @Test
  public void demo01(){
    List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();
    for (int i=1;i<9;i++){
      Map<String,Object> map = new HashMap<>();
      map.put("id",i);
      map.put("name","張三豐"+i);
      list.add(map);
    }
    Stream<Map<String, Object>> s1 = list.stream();
    list.stream().forEach(map-> System.out.println(map));
 
    List<Map<String,Object>> list2 = new ArrayList<Map<String,Object>>();
    for (int i=1;i<5;i++){
      Map<String,Object> map2 = new HashMap<>();
      map2.put("id",i);
      map2.put("grade",i+60);
      list2.add(map2);
    }
    list2.stream().forEach(s-> System.out.println(s));
/**
 * List<Map<Object, Object>> resultList = oneList.stream().map(map -> twoList.stream()
 *         .filter(m -> Objects.equals(m.get("id"), map.get("id")))
 *         .findFirst().map(m -> {
 *           map.putAll(m);
 *           map.put("grade",90);
 *           return map;
 *         }).orElse(null))
      *         .filter(Objects::nonNull).collect(Collectors.toList());
 */
   /* List<Map<String, Object>> resultList2 = list.stream().map(m->{
          m.put("grade",0);
          for (int i=0;i<list2.size();i++){
            if(m.get("id").equals(list2.get(i).get("id"))){
              m.put("grade",list2.get(i).get("grade"));
              break;
            }
          }
          return m;
        }).collect(Collectors.toList());*/
    List<Map<String, Object>> resultList2 = list.stream().map(m->{
      m.put("grade",0);
      list2.stream().filter(m2->Objects.equals(m.get("id"), m2.get("id"))).forEach(s-> m.put("grade",s.get("grade")));
      return m;
    }).collect(Collectors.toList());
    resultList2.stream().forEach(s-> System.out.println(s));
  }

補(bǔ)充知識：Java-8新特性-通過Stream獲取兩個List復(fù)雜對象的交并差集

思路：首先獲取兩個list的id，通過id比較獲取id的交并差集，再通過一次獲取list對象里面的交并差集元素

代碼直接可運(yùn)行，個人覺得java8的stream非常類似ES6的集合運(yùn)算，filter、foreach、map、reduce基本可以一一對應(yīng)

代碼：

package com.stream;
 
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
 
/**
 *
 * @ClassName: TwoListCopare
 * @Description: 兩個List<對象>取交集\并集\差集</>
 **/
public class TwoListCopare {
  public static void main(String[] args) {
    UserDTO userOld1 = new UserDTO("1","aaa",22);
    UserDTO userOld2 = new UserDTO("2","bbb",32);
    UserDTO userOld3 = new UserDTO("3","ccc",11);
    UserDTO userOld4 = new UserDTO("4","ddd",42);
    UserDTO userOld5 = new UserDTO("5","bbb",22);
    UserDTO userOld6 = new UserDTO("6","eee",24);
 
    UserDTO userNew1 = new UserDTO("7","dada",22);   //新增一個
    UserDTO userNew2 = new UserDTO("2","bbb",32);   //不變一個
    UserDTO userNew3 = new UserDTO("3","kaka",33);   //更新一個
    UserDTO userNew4 = new UserDTO("8","dbdb",42);   //新增一個
    UserDTO userNew5 = new UserDTO("5","bbb",100);   //更新一個
    //當(dāng)然，少了1,4,6
 
    List<UserDTO> mapAdd = new ArrayList<>();
 
    List<UserDTO> oldList = new ArrayList<>();
    List<UserDTO> newList = new ArrayList<>();
 
    //添加老數(shù)據(jù)
    oldList.add(userOld1);
    oldList.add(userOld2);
    oldList.add(userOld3);
    oldList.add(userOld4);
    oldList.add(userOld5);
    oldList.add(userOld6);
    //添加新數(shù)據(jù)
    newList.add(userNew1);
    newList.add(userNew2);
    newList.add(userNew3);
    newList.add(userNew4);
    newList.add(userNew5);
 
    //去交集,既獲取id相同的交集，需要更新
    //1.先提取出id和結(jié)果，用map形式
    List<String> oldIds = new ArrayList<>();
    List<String> newIds = new ArrayList<>();
    oldList.stream().forEach(it->oldIds.add(it.getId()));
    newList.stream().forEach(it->newIds.add(it.getId()));
//    oldIds.stream().forEach(System.out::println);
//    newIds.stream().forEach(System.out::println);
 
    //取交集id
    System.out.println("-----------------交集----------------------");
    List<String> collectUpdate = newIds.stream().filter(it -> oldIds.contains(it)).collect(Collectors.toList());
    collectUpdate.stream().forEach(System.out::println);
    //取對應(yīng)交集的對象
    System.out.println("------------------交集的對象---------------------");
    List<UserDTO> userUpdate = newList.stream().filter(it -> collectUpdate.contains(it.getId())).collect(Collectors.toList());
    userUpdate.stream().forEach(System.out::println);
 
    //取old的差集
    System.out.println("-----------------old的差集----------------------");
    List<String> collectDelete = oldIds.stream().filter(it -> !newIds.contains(it)).collect(Collectors.toList());
    collectDelete.stream().forEach((System.out::println));
    //取對應(yīng)old差集對象
    System.out.println("-----------------old差集對象----------------------");
    List<UserDTO> userDelete = oldList.stream().filter(it -> collectDelete.contains(it.getId())).collect(Collectors.toList());
    userDelete.stream().forEach(System.out::println);
 
    //取new的差集
    System.out.println("-----------------new的差集----------------------");
    List<String> collectAdd = newIds.stream().filter(it -> !oldIds.contains(it)).collect(Collectors.toList());
    collectAdd.stream().forEach((System.out::println));
    //取對應(yīng)old差集對象
    System.out.println("-------------------old差集對象--------------------");
    List<UserDTO> userAdd = newList.stream().filter(it -> collectAdd.contains(it.getId())).collect(Collectors.toList());
    userAdd.stream().forEach(System.out::println);
 
    //取并集
    System.out.println("-------------------并集--------------------");
    List<String> allIds = new ArrayList<>();
    //獲取一個包含了oldIds和newIds的總結(jié)合,但是沒有去重
    allIds.addAll(oldIds);
    allIds.addAll(newIds);
    //去重，獲取并集ids的新集合
    List<String> joinIds = allIds.stream().distinct().collect(Collectors.toList());
    joinIds.stream().forEach(System.out::println);
  }
}

結(jié)果：