Java 使用 Stream 去重

根据对象单个属性进行去重

在项目中可以会获取到一个集合，集合中有很多重复的数据，但是总感觉转成Set去重不太体面，那就可以试试使用 Stream 来实现根据对象的属性进行去重

将集合转为Stream流后通过Collectors.toMap 进行去重

• UserEntity::getName 指定根据名字去重
• user -> user 执行后要转换的类型(因为我们不需要转换所以不处理)
• (u1, u2) -> u1) 然后存在多个时我们保留第一个对象

@Testpublic void propertyDistinct(){UserEntity a1 = new UserEntity().setId(1).setStatus(1).setName("A1");UserEntity a2 = new UserEntity().setId(2).setStatus(2).setName("A2");UserEntity a3 = new UserEntity().setId(3).setStatus(3).setName("A3");UserEntity a4 = new UserEntity().setId(4).setStatus(4).setName("A1");UserEntity a5 = new UserEntity().setId(5).setStatus(3).setName("A5");UserEntity a6 = new UserEntity().setId(6).setStatus(2).setName("A3");UserEntity a7 = new UserEntity().setId(7).setStatus(4).setName("A2");List<UserEntity> userList = Arrays.asList(a1, a2, a3, a4, a5, a6, a7);List<UserEntity> list = userList.stream().collect(Collectors.toMap(UserEntity::getName, user -> user, (u1, u2) -> u1)).values().stream().collect(Collectors.toList());list.forEach(System.out::println);}实现结果：UserEntity(id=1, code=null, status=1, name=A1, sex=null, birthday=null, pingList=null)UserEntity(id=2, code=null, status=2, name=A2, sex=null, birthday=null, pingList=null)UserEntity(id=3, code=null, status=3, name=A3, sex=null, birthday=null, pingList=null)UserEntity(id=5, code=null, status=3, name=A5, sex=null, birthday=null, pingList=null)

根据对象多个属性进行去重

根据集合对象中的 Id+“-”+Name 进行去重

@Testpublic void propertyDistinct(){UserEntity a1 = new UserEntity().setId(1).setStatus(1).setName("A1");UserEntity a2 = new UserEntity().setId(2).setStatus(2).setName("A2");UserEntity a3 = new UserEntity().setId(3).setStatus(3).setName("A3");UserEntity a4 = new UserEntity().setId(1).setStatus(4).setName("A1");UserEntity a5 = new UserEntity().setId(5).setStatus(3).setName("A5");UserEntity a6 = new UserEntity().setId(6).setStatus(2).setName("A3");UserEntity a7 = new UserEntity().setId(7).setStatus(4).setName("A2");List<UserEntity> userList = Arrays.asList(a1, a2, a3, a4, a5, a6, a7);List<UserEntity> uniqueList = userList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getId() + "-" + o.getName()))),ArrayList::new));uniqueList.forEach(System.out::println); }实现结果：UserEntity(id=1, code=null, status=1, name=A1, sex=null, birthday=null, pingList=null)UserEntity(id=2, code=null, status=2, name=A2, sex=null, birthday=null, pingList=null)UserEntity(id=3, code=null, status=3, name=A3, sex=null, birthday=null, pingList=null)UserEntity(id=5, code=null, status=3, name=A5, sex=null, birthday=null, pingList=null)UserEntity(id=6, code=null, status=2, name=A3, sex=null, birthday=null, pingList=null)UserEntity(id=7, code=null, status=4, name=A2, sex=null, birthday=null, pingList=null)

根据对象所有属性进行去重

使用的 stream 的 distinct() 方法必须对象属性都相同

@Testpublic void propertyDistinct(){UserEntity a1 = new UserEntity().setId(1).setStatus(1).setName("A1");UserEntity a2 = new UserEntity().setId(2).setStatus(2).setName("A2");UserEntity a3 = new UserEntity().setId(3).setStatus(3).setName("A3");UserEntity a4 = new UserEntity().setId(1).setStatus(1).setName("A1");UserEntity a5 = new UserEntity().setId(5).setStatus(3).setName("A5");UserEntity a6 = new UserEntity().setId(3).setStatus(3).setName("A3");UserEntity a7 = new UserEntity().setId(7).setStatus(4).setName("A2");List<UserEntity> userList = Arrays.asList(a1, a2, a3, a4, a5, a6, a7);List<UserEntity> uniqueList = userList.stream().distinct().collect(Collectors.toList());uniqueList.forEach(System.out::println);}实现结果：UserEntity(id=1, code=null, status=1, name=A1, sex=null, birthday=null, pingList=null)UserEntity(id=2, code=null, status=2, name=A2, sex=null, birthday=null, pingList=null)UserEntity(id=3, code=null, status=3, name=A3, sex=null, birthday=null, pingList=null)UserEntity(id=5, code=null, status=3, name=A5, sex=null, birthday=null, pingList=null)UserEntity(id=7, code=null, status=4, name=A2, sex=null, birthday=null, pingList=null)