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前言

对于list集合进行去重操作,多种情况进行记录.

只记录在学习与实践过程中需要对集合操作的场景,方便下次能够直接快速的回忆起来.

当然这些方法的使用与操作皆是对于Java8的stream操作,TreeSet不重复特性进行的运用.

如果能够更好更快的达成目的,也是不必拘泥于某一些固定的方式去处理数据,以效率与程序开销优先.

正文

数据对象

将数据对象写成静态不可变的list来方便我们对于程序进行调用验证

private static final List<SyncBalance> list = asList(new SyncBalance(BigDecimal.ZERO, "12345678", 0, 1, "GGBond", 32, 0),new SyncBalance(BigDecimal.ZERO, "22345678", 0, 1, "GGBond", 32, 0),new SyncBalance(BigDecimal.ZERO, "22345678", 1, 1, "GGBond", 32, 0),new SyncBalance(BigDecimal.ZERO, "22345678", 1, 1, "GGBond", 32, 0)
);

1. 对象整体去重

/*** 1. 对所有属性一样的数据进行去重*/
public static void allColumnDistinct() {List<SyncBalance> allColumnDistinct = list.stream().distinct().collect(Collectors.toList());
}

2. 单个属性去重(只返回属性)

/*** 2. 对单个属性去重，只返回去重的属性*/
public static void columnDistinct() {List<String> columnDistinct = list.stream().map(SyncBalance::getMobile).distinct().collect(Collectors.toList());
}

3. 单个属性去重

/*** 3-1. 对单个属性一样的数据进行去重，下面是对`mobile`去重*/
public static void oneColumnDistinctMethodOne() {List<SyncBalance> oneColumnDistinctMethodOne = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(SyncBalance::getMobile))), ArrayList::new));
}

/*** 3-2. 对单个属性一样的数据进行去重,下面是对`mobile`去重(通过自定义属性去重方法)*/
public static void oneColumnDistinctMethodTwo() {List<SyncBalance> oneColumnDistinctMethodTwo = list.stream().filter(distinctByKey(i -> i.getMobile())).collect(Collectors.toList());
}/**
* list对象单个个字段去重(自定义属性)
* @param keyExtractor 去重的对象字段
* @return
* @param <T>
*/
public static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {Map<Object, Boolean> seen = new ConcurrentHashMap<>();return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
}

/*** 3-3. 对单个属性一样的数据进行去重,下面是对`mobile`去重* 利用TreeSet进行去重*/
public static void oneColumnDistinctMethodThree() {TreeSet<SyncBalance> oneColumnDistinctMethodThree = new TreeSet<>(Comparator.comparing(i -> i.getMobile()));list.forEach(a -> oneColumnDistinctMethodThree.add(a));
}

4. 多个属性去重

/*** 4. 多个字段条件去重*/
public static void twoColumnDistinct() {List<SyncBalance> twoColumnDistinct = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(p -> p.getMobile() + ";" + p.getStatus()))), ArrayList::new));
}

验证方法

对于验证方法添加了一些分隔的数据

/*** 验证的main方法* @param args*/
public static void main(String[] args) {allColumnDistinct();columnDistinct();oneColumnDistinctMethodOne();oneColumnDistinctMethodTwo();oneColumnDistinctMethodThree();twoColumnDistinct();
}

运行结果

allColumnDistinct---v
SyncBalance(accountBalance=0, mobile=12345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
SyncBalance(accountBalance=0, mobile=22345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
SyncBalance(accountBalance=0, mobile=22345678, status=1, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
allColumnDistinct---^
columnDistinct---v
12345678
22345678
columnDistinct---^
oneColumnDistinctMethodOne---v
SyncBalance(accountBalance=0, mobile=12345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
SyncBalance(accountBalance=0, mobile=22345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
oneColumnDistinctMethodOne---^
oneColumnDistinctMethodTwo---v
SyncBalance(accountBalance=0, mobile=12345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
SyncBalance(accountBalance=0, mobile=22345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
oneColumnDistinctMethodTwo---^
oneColumnDistinctMethodThree---v
SyncBalance(accountBalance=0, mobile=12345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
SyncBalance(accountBalance=0, mobile=22345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
oneColumnDistinctMethodThree---^
twoColumnDistinct---v
SyncBalance(accountBalance=0, mobile=12345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
SyncBalance(accountBalance=0, mobile=22345678, status=0, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
SyncBalance(accountBalance=0, mobile=22345678, status=1, sysId=1, loginAccountName=GGBond, keepOrUpdate=32, id=0)
twoColumnDistinct---^

结尾

集合的操作不止拘泥于stream流与TreeSet可以处理,其他一下如果可以实现皆可使用.

以上,皆可直接使用.