集合处理利器CollectionsUtil

在我们日常开发工作中, 大部分时间其实都是在和 JAVA集合框架打交道,对集合框架使用溜的话,会非常快捷,下面特别封装十分常用的方法

主要由下面8部分组成:

CollectionsUtil

1.辅助添加

方法	Description
addAllIgnoreNull(Collection, Iterable<? extends O>)	添加所有的Iterable元素到指定的objectCollection,如果 iterable是null将忽略.
addIgnoreNullOrEmpty(Collection, T)	添加 element元素到指定的objectCollection,如果 element 是null或者 empty将忽略.

1.1 addAllIgnoreNull(Collection, Iterable<? extends O>)

对于以下代码:

private Set<String> getItemComboIds(List<ShoppingCartLineCommand> lines){
 Set<String> set = new HashSet<>();
 if (null != lines && lines.size() > 0){
     for (ShoppingCartLineCommand line : lines){
         if (line.getComboIds() != null){
             set.addAll(line.getComboIds());
         }
     }
 }
 return set;
}

**可以重构成: **

private Set<String> getItemComboIds(List<ShoppingCartLineCommand> lines){
 if (isNullOrEmpty(lines)){
     return Collections.emptySet();
 }
 Set<String> set = new HashSet<>();
 for (ShoppingCartLineCommand line : lines){
     CollectionsUtil.addAllIgnoreNull(set, line.getComboIds());
 }
 return set;
}

重构之后,方法的复杂度会更小,阅读性更高

1.2 addIgnoreNullOrEmpty(Collection, T)

对于以下代码:

List<Object[]> dataList = new ArrayList<>();
for (T bean : iterable){
 Object[] objectArray = toObjectArray(bean, propertyNameList);
 if (isNotNullOrEmpty(objectArray)){
     dataList.add(objectArray);
 }
}
return dataList;

**可以重构成: **

List<Object[]> dataList = new ArrayList<>();
for (T bean : iterable){
 addIgnoreNullOrEmpty(dataList, toObjectArray(bean, propertyNameList));
}
return dataList;

重构之后,方法的复杂度会更小,阅读性更高

2.查找

方法	Description
find(Iterable, String, V)	找到 iterable中,第一个 propertyName属性名称值是 propertyValue 的对应元素.
find(Iterable, Predicate)	迭代查找匹配predicate 的第一个元素并返回.

2.1 find(Iterable, String, V)

比如以下代码:

public Boolean hasDistributionMode(CalcFreightCommand calcFreightCommand,Long shopId){
    // 通过收货地址获取支持的物流方式
    List<DistributionMode> distributionModeList = findDistributeMode(
                    shopId,
                    calcFreightCommand.getProvienceId(),
                    calcFreightCommand.getCityId(),
                    calcFreightCommand.getCountyId(),
                    calcFreightCommand.getTownId());

    Boolean flag = false;
    if (Validator.isNotNullOrEmpty(distributionModeList)){
        if (null != calcFreightCommand.getDistributionModeId()){
            for (DistributionMode distributionMode : distributionModeList){
                if (distributionMode.getId().equals(calcFreightCommand.getDistributionModeId())){
                    flag = true;
                }
            }
        }else{
            flag = true;
        }
    }
    return flag;
}

22行代码,可以重构成

public Boolean hasDistributionMode(CalcFreightCommand calcFreightCommand,Long shopId){
    // 通过收货地址获取支持的物流方式
    List<DistributionMode> distributionModeList = findDistributeMode(shopId, calcFreightCommand.getProvienceId(), calcFreightCommand.getCityId(), calcFreightCommand.getCountyId(), calcFreightCommand.getTownId());

    if (isNullOrEmpty(distributionModeList)){
        return false;
    }

    if (isNullOrEmpty(calcFreightCommand.getDistributionModeId())){
        return true;
    }

    DistributionMode distributionMode = CollectionsUtil.find(distributionModeList, "id", calcFreightCommand.getDistributionModeId());
    return null != distributionMode;
}

只需要14行代码,而且可阅读性更高

2.2 find(Iterable, Predicate)

场景: 从list中查找name是 关羽,并且 age等于30的User对象

List<User> list = toList(//
             new User("张飞", 23),
             new User("关羽", 24),
             new User("刘备", 25),
             new User("关羽", 30));

Map<String, Object> map = new HashMap<>();
map.put("name", "关羽");
map.put("age", 30);

Predicate<User> predicate = BeanPredicateUtil.equalPredicate(map);

User user = CollectionsUtil.find(list, predicate);
LOGGER.debug(JsonUtil.format(user));

返回:

{
"age": 30,
"name": "关羽"
}

3. 定位

方法	Description
indexOf(List, String, V)	在list中,查找第一个属性 propertyName 值是指定值 propertyValue 对象的索引位置.

示例:

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("关羽", 24));
list.add(new User("刘备", 25));

CollectionsUtil.indexOf(list, "name", "张飞")                          =   0

CollectionsUtil.indexOf(null, "age", 24)                             =   -1
CollectionsUtil.indexOf(new ArrayList<User>(), "age", 24)    =   -1

说明:

• 常用于浏览历史记录,当前的商品id是否在历史记录中第一条位置,如果是,可能就不会操作Cookie,诸如此类的操作

4. 查询

方法	Description
select(Collection, String, V...)	循环 objectCollection,获得元素 bean的 propertyName的值,判断是否在propertyValues 数组中;如果在,将该对象存入list中返回.
select(Collection, String, Collection)	循环 objectCollection,获得元素 bean 的propertyName的值,判断是否在propertyValueList 集合中;如果在,将该对象存入list中返回.
select(Collection, Predicate)	按照指定的 Predicate,返回查询出来的集合.

4.1 select(Collection, String, V...)

循环 objectCollection,获得元素 bean的 propertyName的值,判断是否在propertyValues 数组中;如果在,将该对象存入list中返回.

注意:

• 查询的结果的顺序按照原来 objectCollection里面的顺序,和参数 propertyValues 无关,如果你需要结果里面的元素按照指定的propertyValues 顺序排序的话,可以将结果再调用SortUtil.sortListByFixedOrderPropertyValueArray(List, String, Object)

示例:

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("关羽", 24));
list.add(new User("刘备", 25));

String[] array = { "刘备", "关羽" };
LOGGER.info(JsonUtil.format(CollectionsUtil.select(list, "name", array)));

返回:

[{
       "age": 24,
       "name": "关羽"
   },{
       "age": 25,
       "name": "刘备"
}]

4.2 select(Collection, String, Collection)

循环 objectCollection,获得元素 bean 的propertyName的值,判断是否在propertyValueList 集合中;如果在,将该对象存入list中返回.

说明:

• 查询的结果的顺序按照原来 objectCollection里面的顺序,和参数 propertyValueList 无关,如果你需要结果里面的元素按照指定的 propertyValueList顺序排序的话,可以将结果再调用SortUtil.sortListByFixedOrderPropertyValueList(List, String, List)

• 和该方法正好相反的是 selectRejected(Collection, String, Collection)

示例: 场景: 查询 name属性是"张飞"或者是"刘备"的 User list

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("关羽", 24));
list.add(new User("刘备", 25));

List<String> propertyValueList = new ArrayList<>();
propertyValueList.add("张飞");
propertyValueList.add("刘备");
LOGGER.info(JsonUtil.format(CollectionsUtil.select(list, "name", propertyValueList)));

返回:

[{
            "age": 23,
            "name": "张飞"
        },{
            "age": 25,
            "name": "刘备"
 }]

重构:

对于以下代码:

// 当前店铺 的物流方式Id set
Set<Long> distributionModeIdSet = new HashSet<>();
for (TemeplateDistributionMode tdCmd : temeplateDistributionModeList){
 distributionModeIdSet.add(tdCmd.getDistributionModeId());
}

// 拿到所有的物流方式 列表
List<DistributionCommand> distributionCommandList = freigthMemoryManager.getDistributionList();

// 根据 物流方式ID 找出 支持本商铺的 DistributionCommand
List<DistributionCommand> curShopDistributionCommandList = new ArrayList<>();

for (Long modeId : distributionModeIdSet){
 for (DistributionCommand distributionCmd : distributionCommandList){
     if (modeId.equals(distributionCmd.getDistributionModeId())){
         curShopDistributionCommandList.add(distributionCmd);
     }
 }
}

可以重构成:

// 当前店铺 的物流方式Id set
Set<Long> distributionModeIdSet = CollectionsUtil.getPropertyValueSet(temeplateDistributionModeList, "distributionModeId");
// 拿到所有的物流方式 列表
List<DistributionCommand> distributionCommandList = freigthMemoryManager.getDistributionList();

// 根据 物流方式ID 找出 支持本商铺的 DistributionCommand
List<DistributionCommand> curShopDistributionCommandList = CollectionsUtil.select(distributionCommandList, "distributionModeId", distributionModeIdSet);

4.3 select(Collection, Predicate)

按照指定的 Predicate,返回查询出来的集合.

说明:

• 和该方法正好相反的是 selectRejected(Collection, Predicate)

示例1: 场景: 查找等于 1的元素

List<Long> list = new ArrayList<>();
list.add(1L);
list.add(1L);
list.add(2L);
list.add(3L);
LOGGER.info(JsonUtil.format(CollectionsUtil.select(list, new EqualPredicate<Long>(1L))));

返回:

[1,1]

示例2: 场景: 查找大于 10的元素

Comparator<Integer> comparator = ComparatorUtils.naturalComparator();
Predicate<Integer> predicate = new ComparatorPredicate<Integer>(10, comparator, Criterion.LESS);

List<Integer> select = CollectionsUtil.select(toList(1, 5, 10, 30, 55, 88, 1, 12, 3), predicate);
LOGGER.debug(JsonUtil.format(select, 0, 0));

返回:

[30,55,88,12]

5. 反查

方法	Description
selectRejected(Collection, String, V...)	循环 objectCollection,获得元素 bean 的 propertyName 属性值都不在 propertyValues 时候的list.
selectRejected(Collection, String, Collection)	循环 objectCollection,获得元素 bean 的 propertyName的值,判断是否不在propertyValueList 集合中;如果不在,将该对象存入list中返回.
selectRejected(Collection, Predicate)	循环 objectCollection,获得元素 bean,判断是否不匹配predicate,如果不匹配 ,将该对象存入list中返回.

5.1 selectRejected(Collection, String, V...)

循环 objectCollection,获得元素 bean 的 propertyName 属性值都不在 propertyValues 时候的list.

示例: 场景: 查询name 不是刘备 也不是张飞的 User list元素

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("关羽", 24));
list.add(new User("刘备", 25));

List<User> selectRejected = CollectionsUtil.selectRejected(list, "name", "刘备", "张飞");
LOGGER.info(JsonUtil.format(selectRejected));

返回:

[{
"age": 24,
"name": "关羽"
}]

5.2 selectRejected(Collection, String, Collection)

循环 objectCollection,获得元素 bean 的 propertyName的值,判断是否不在propertyValueList 集合中;如果不在,将该对象存入list中返回.

示例: 场景: 查询 name属性是不是"张飞",也不是"刘备"的 User list

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("关羽", 24));
list.add(new User("刘备", 25));

List<String> propertyValueList = new ArrayList<>();
propertyValueList.add("张飞");
propertyValueList.add("刘备");
LOGGER.info(JsonUtil.format(CollectionsUtil.selectRejected(list, "name", propertyValueList)));

返回:

[{
"age": 24,
"name": "关羽"
}]

5.3 selectRejected(Collection, Predicate)

循环 objectCollection,获得元素 bean,判断是否不匹配predicate,如果不匹配 ,将该对象存入list中返回.

说明:

• 和该方法正好相反的是 select(Collection, Predicate)

示例: 场景: 从list中查找不等于1的元素

List<Long> list = toList(1L, 1L, 2L, 3L);
CollectionsUtil.selectRejected(list, new EqualPredicate<Long>(1L));

返回:

2L, 3L

6. 提取

方法	Description
getPropertyValueList(Collection, String)	循环集合 objectCollection,取到对象指定的属性 propertyName的值,拼成List(ArrayList).
getPropertyValueSet(Collection, String)	解析迭代集合 objectCollection ,取到对象指定的属性 propertyName的值,拼成Set(LinkedHashSet).
getPropertyValueMap(Collection, String, String)	循环 objectCollection ,以 keyPropertyName属性值为key, valuePropertyName属性值为value,组成map返回.

6.1 getPropertyValueList(Collection, String)

循环集合 objectCollection,取到对象指定的属性 propertyName的值,拼成List(ArrayList).

示例:

场景: 获取user list每个元素的id属性值,组成新的list返回

List<User> list = toList(//
             new User(2L),
             new User(5L),
             new User(5L));

List<Long> resultList = CollectionsUtil.getPropertyValueList(list, "id");
LOGGER.debug(JsonUtil.format(resultList));

返回:

[2,5,5]

6.2 getPropertyValueSet(Collection, String)

解析迭代集合 objectCollection ,取到对象指定的属性 propertyName的值,拼成Set(LinkedHashSet).

说明:

返回的是 LinkedHashSet,顺序是参数 objectCollection 元素的顺序

示例:

List<User> list = new ArrayList<>();
list.add(new User(2L));
list.add(new User(5L));
list.add(new User(5L));

LOGGER.info(JsonUtil.format(CollectionsUtil.getPropertyValueSet(list, "id")));

返回:

 [2,5]

6.3 getPropertyValueMap(Collection, String, String)

循环 objectCollection ,以 keyPropertyName属性值为key, valuePropertyName属性值为value,组成map返回.

说明:

• 返回的是 LinkedHashMap,顺序是参数 objectCollection 元素的顺序

• 如果有元素 keyPropertyName属性值相同,那么后面的值会覆盖前面的值

示例:

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("关羽", 24));
list.add(new User("刘备", 25));

LOGGER.info(JsonUtil.format(CollectionsUtil.getPropertyValueMap(list, "name", "age")));

返回:

{
"张飞": 23,
"关羽": 24,
"刘备": 25
}

如果有元素 keyPropertyName属性值相同,那么后面的值会覆盖前面的值

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("关羽", 24));
list.add(new User("张飞", 25));

LOGGER.info(JsonUtil.format(CollectionsUtil.getPropertyValueMap(list, "name", "age")));

返回:

{
"张飞": 25,
"关羽": 24,
}

7. 分组

方法	Description
group(Collection, String)	循环 objectCollection,以 元素的 propertyName属性值为key,相同值的元素组成list作为value,封装成map返回.
group(Collection, String, Predicate)	循环 objectCollection,找到符合条件的 includePredicate的元素,以元素的 propertyName 属性值为key,相同值的元素组成list作为value,封装成map返回.
group(Collection, Transformer<O, T>)	循环 objectCollection,将元素使用keyTransformer转成key,相同值的元素组成list作为value,封装成map返回.
group(Collection, Predicate, Transformer<O, T>)	循环 objectCollection,找到符合条件的 includePredicate的元素,将元素使用keyTransformer转成key ,相同值的元素组成list作为value,封装成map返回.
groupOne(Collection, String)	循环 objectCollection,以元素的 propertyName属性值为key,元素为value,封装成map返回(map只put第一个匹配的元素,后面出现相同的元素将会忽略).

7.1 group(Collection, String)

循环 objectCollection,以 元素的 propertyName属性值为key,相同值的元素组成list作为value,封装成map返回.

说明:

• 返回的LinkedHashMap,key是 objectCollection中的元素对象中 propertyName的值,value是objectCollection 中的元素对象;

• 顺序是 objectCollection propertyName的值顺序,如果需要排序,可自行调用 SortUtil.sortMapByKeyAsc(Map), SortUtil.sortMapByKeyDesc(Map), SortUtil.sortMapByValueAsc(Map), SortUtil.sortMapByValueDesc(Map)或者, SortUtil.sortMap(Map, java.util.Comparator)

• 属性propertyName值相同的元素,组成集合 list

• 如果value只需要单值的话,可以调用 groupOne(Collection, String)方法

示例:

List<User> list = toList(
             new User("张飞", 23),
             new User("刘备", 25),
             new User("刘备", 30));

Map<String, List<User>> map = CollectionsUtil.group(list, "name");
LOGGER.debug(JsonUtil.format(map));

返回:

{
    "张飞": [ {
        "age": 23,
        "name": "张飞",
    }],
    "刘备": [
        {
            "age": 25,
            "name": "刘备",
        },
        {
            "age": 30,
            "name": "刘备",
        }
    ]
}

7.2 group(Collection, String, Predicate)

循环 objectCollection,找到符合条件的 includePredicate的元素,以元素的 propertyName 属性值为key,相同值的元素组成list作为value,封装成map返回.

说明:

• 返回的LinkedHashMap,key是 objectCollection中的元素对象中 propertyName的值,value是objectCollection 中的元素对象;

• 顺序是 objectCollection propertyName的值顺序,如果需要排序,可自行调用 SortUtil.sortMapByKeyAsc(Map), SortUtil.sortMapByKeyDesc(Map), SortUtil.sortMapByValueAsc(Map), SortUtil.sortMapByValueDesc(Map)或者, SortUtil.sortMap(Map, java.util.Comparator)

示例:

场景: 将age > 20的User,按照name 进行 group

List<User> list = new ArrayList<>();
list.add(new User("张飞", 10));
list.add(new User("张飞", 28));
list.add(new User("刘备", 32));
list.add(new User("刘备", 30));
list.add(new User("刘备", 10));

Map<String, List<User>> map = CollectionsUtil.group(list, "name", new Predicate<User>(){

    @Override
    public boolean evaluate(User user){
        return user.getAge() > 20;
    }
});
LOGGER.info(JsonUtil.format(map));

返回:

{
    "张飞": [{
        "age": 28,
        "name": "张飞"
    }],
    "刘备": [{
            "age": 32,
            "name": "刘备"
        },{
            "age": 30,
            "name": "刘备"
        }
    ]
}

当然,对于上述代码,你还可以优化成:

Predicate<User> comparatorPredicate = BeanPredicateUtil.comparatorPredicate("age", 20, Criterion.LESS);
Map<String, List<User>> map = CollectionsUtil.group(list, "name", comparatorPredicate);

7.3 group(Collection, Transformer<O, T>)

循环 objectCollection,将元素使用keyTransformer转成key,相同值的元素组成list作为value,封装成map返回.

说明:

• 返回的LinkedHashMap,key是 objectCollection中的元素 使用keyTransformer转换的值,value是 objectCollection中的元素对象(相同key值,组成list);

• 返回的LinkedHashMap顺序,是 objectCollection 元素顺序,如果需要排序,可自行调用 SortUtil.sortMapByKeyAsc(Map), SortUtil.sortMapByKeyDesc(Map), SortUtil.sortMapByValueAsc(Map), SortUtil.sortMapByValueDesc(Map)或者, SortUtil.sortMap(Map, java.util.Comparator)

示例: 场景: 从user list中,提取user的姓名的姓为key,user组成list,返回map

User mateng55 = new User("马腾", 55);
User machao28 = new User("马超", 28);
User madai27 = new User("马岱", 27);
User maxiu25 = new User("马休", 25);
User zhangfei28 = new User("张飞", 28);
User liubei32 = new User("刘备", 32);
User guanyu50 = new User("关羽", 50);
User guanping32 = new User("关平", 32);
User guansuo31 = new User("关索", 31);
User guanxing20 = new User("关兴", 18);

//************************************************************************
List<User> list = toList(mateng55, machao28, madai27, maxiu25, zhangfei28, liubei32, guanyu50, guanping32, guansuo31, guanxing20);

//************************************************************************

Map<String, List<User>> map = CollectionsUtil.group(list,new Transformer<User, String>(){

 @Override
 public String transform(User user){
     //提取名字 的姓
     return user.getName().substring(0, 1);
 }
});

LOGGER.debug(JsonUtil.format(map));

返回:

{
    "马":[{
            "age": 55,
            "name": "马腾",
        },{
            "age": 28,
            "name": "马超",
        },{
            "age": 27,
            "name": "马岱",
        },{
            "age": 25,
            "name": "马休",
        }
    ],
    "张": [{
        "age": 28,
        "name": "张飞",
    }],
    "刘": [{
        "age": 32,
        "name": "刘备",
    }],
    "关": [{
            "age": 50,
            "name": "关羽",
        },{
            "age": 32,
            "name": "关平",
        },{
            "age": 31,
            "name": "关索",
        },{
            "age": 18,
            "name": "关兴",
        }
    ]
}

7.4 group(Collection, Predicate, Transformer<O, T>)

循环 objectCollection,找到符合条件的 includePredicate的元素,将元素使用keyTransformer转成key ,相同值的元素组成list作为value,封装成map返回.

说明:

• 返回的LinkedHashMap,key是 objectCollection中的元素 使用keyTransformer转换的值,value是 objectCollection中的元素对象(相同key值,组成list);

• 返回的LinkedHashMap顺序,是 objectCollection 元素顺序,如果需要排序,可自行调用 SortUtil.sortMapByKeyAsc(Map), SortUtil.sortMapByKeyDesc(Map), SortUtil.sortMapByValueAsc(Map), SortUtil.sortMapByValueDesc(Map)或者, SortUtil.sortMap(Map, java.util.Comparator)

示例: 场景: 从user list中,提取 年龄 大于20的user,user的姓名的姓为key,user组成list,返回map

User mateng55 = new User("马腾", 55);
User machao28 = new User("马超", 28);
User madai27 = new User("马岱", 27);
User maxiu25 = new User("马休", 25);
User zhangfei28 = new User("张飞", 28);
User liubei32 = new User("刘备", 32);
User guanyu50 = new User("关羽", 50);
User guanping32 = new User("关平", 32);
User guansuo31 = new User("关索", 31);
User guanxing20 = new User("关兴", 18);

//************************************************************************
List<User> list = toList(mateng55, machao28, madai27, maxiu25, zhangfei28, liubei32, guanyu50, guanping32, guansuo31, guanxing20);

//************************************************************************

Predicate<User> comparatorPredicate = BeanPredicateUtil.comparatorPredicate("age", 20, Criterion.LESS);
Map<String, List<User>> map = CollectionsUtil.group(list, comparatorPredicate, new Transformer<User, String>(){

 @Override
 public String transform(User user){
     //提取名字 的姓
     return user.getName().substring(0, 1);
 }
});

LOGGER.debug(JsonUtil.format(map));

返回:

{
    "马":[{
            "age": 55,
            "name": "马腾",
        },{
            "age": 28,
            "name": "马超",
        },{
            "age": 27,
            "name": "马岱",
        },{
            "age": 25,
            "name": "马休"
        }],
    "张": [{
        "age": 28,
        "name": "张飞"
    }],
    "刘": [{
        "age": 32,
        "name": "刘备"
    }],
    "关": [{
            "age": 50,
            "name": "关羽"
        },{
            "age": 32,
            "name": "关平"
        },{
            "age": 31,
            "name": "关索"
        }]
}

7.5 groupOne(Collection, String)

循环 objectCollection,以元素的 propertyName属性值为key,元素为value,封装成map返回(map只put第一个匹配的元素,后面出现相同的元素将会忽略).

说明:

• 返回的LinkedHashMap,key是 objectCollection中的元素对象中 propertyName的值,value是 objectCollection中的元素对象;

• 顺序是 objectCollection propertyName的值 顺序,如果需要排序,可自行调用 SortUtil.sortMapByKeyAsc(Map), SortUtil.sortMapByKeyDesc(Map), SortUtil.sortMapByValueAsc(Map), SortUtil.sortMapByValueDesc(Map)或者, SortUtil.sortMap(Map, java.util.Comparator)

• 间接的可以做到基于某个属性值去重的效果

• 如果value需要是集合的话,可以调用 group(Collection, String)方法

示例:

List<User> list = new ArrayList<>();
list.add(new User("张飞", 23));
list.add(new User("刘备", 25));
list.add(new User("刘备", 30));

Map<String, User> map = CollectionsUtil.groupOne(list, "name");
LOGGER.info(JsonUtil.format(map));

返回:

{
    "张飞":         {
        "age": 23,
        "name": "张飞"
    },
    "刘备":         {
        "age": 25,
        "name": "刘备"
    }
}

8.删除

方法	Description
remove(Collection, O)	从 objectCollection中 删除removeElement (原集合对象不变).
removeAll(Collection, Collection)	从 objectCollection中删除所有的 removeCollection (原集合对象不变).
removeDuplicate(Collection)	去重,返回没有重复元素的新list (原集合对象不变).

8.1 remove(Collection, O)

从 objectCollection中 删除removeElement (原集合对象不变).

说明:

• 返回剩余的集合 (原集合对象不变),这个方法非常有用,如果你不想修改 collection的话,不能调用 collection.remove(removeElement);.

• 底层实现是调用的 ListUtils.removeAll(Collection, Collection),将不是removeElement 的元素加入到新的list返回.

示例:

List<String> list = new ArrayList<>();
list.add("xinge");
list.add("feilong1");
list.add("feilong2");
list.add("feilong2");

LOGGER.info(JsonUtil.format(CollectionsUtil.remove(list, "feilong2")));

返回:

["xinge","feilong1"]

此时,原来的list不变:

LOGGER.info(JsonUtil.format(list));

**输出 : **

["xinge","feilong1","feilong2","feilong2"]

8.2 removeAll(Collection, Collection)

从 objectCollection中删除所有的 removeCollection (原集合对象不变).

说明:

• 返回剩余的集合 (原集合对象objectCollection不变),如果你不想修改 objectCollection的话,不能直接调用 collection.removeAll(remove);,这个方法非常有用.

• 底层实现是调用的 ListUtils.removeAll(Collection, Collection),将不是removeElement的元素加入到新的list返回.

示例: 场景: 从list中删除 "feilong2","feilong1"元素

List<String> list = toList("xinge", "feilong1", "feilong2", "feilong2");
List<String> removeList = CollectionsUtil.removeAll(list, toList("feilong2", "feilong1"));

返回:

["xinge"]

8.3 removeDuplicate(Collection)

去重,返回没有重复元素的新list (原集合对象不变).

示例:

List<String> list = new ArrayList<>();
list.add("feilong1");
list.add("feilong2");
list.add("feilong2");
list.add("feilong3");

LOGGER.info(JsonUtil.format(CollectionsUtil.removeDuplicate(list)));

返回:

["feilong1","feilong2","feilong3"]

注意:

• 如果原 objectCollection 是有序的,那么返回的结果参照原 objectCollection元素顺序

• 原 objectCollection不变

9.转换

方法	Description
collect(Iterable, Transformer<? super O, ? extends T>)	循环 inputIterable,将每个元素使用 transformer 转换成新的对象,返回新的list.
collect(Iterator, Transformer<? super O, ? extends T>)	循环 inputIterator,将每个元素使用 transformer 转换成新的对象 返回新的list.
collect(Iterable inputBeanIterable, Class outputListBeanType, String... includePropertyNames)	循环 inputBeanIterable,将每个元素使用转换程成新的 outputListBeanType 类型对象(如有需要只copy传入的includePropertyNames属性) 返回新的list..

9.1 collect(Iterable, Transformer<? super O, ? extends T>)

循环 inputIterable,将每个元素使用 transformer 转换成新的对象,返回新的list.

示例:

List<String> list = new ArrayList<>();
list.add("xinge");
list.add("feilong1");
list.add("feilong2");
list.add("feilong2");

Transformer<String, Object> nullTransformer = TransformerUtils.nullTransformer();
List<Object> collect = CollectionsUtil.collect(list, nullTransformer);
LOGGER.info(JsonUtil.format(collect, 0, 0));

返回:

[null,null,null,null]

更多的,使用这个方法来处理两个不同类型的转换:

• 比如购物车功能,有游客购物车CookieShoppingCartLine以及内存购物车对象 ShoppingCartLineCommand,两个数据结构部分元素相同,

• 用户登陆需要把cookie中的购物车转成内存购物车ShoppingCartLineCommand list,这时我们可以先创建ToShoppingCartLineCommandTransformer

**代码示例: **

class ToShoppingCartLineCommandTransformer implements Transformer<CookieShoppingCartLine, ShoppingCartLineCommand>{

 private static final String[] COPY_PROPERTY_NAMES = {"skuId","extentionCode","quantity","createTime","settlementState","lineGroup" };

 public ShoppingCartLineCommand transform(CookieShoppingCartLine cookieShoppingCartLine){
     // 将cookie中的购物车 转换为 shoppingCartLineCommand
     ShoppingCartLineCommand shoppingLineCommand = new ShoppingCartLineCommand();
     PropertyUtil.copyProperties(shoppingLineCommand, cookieShoppingCartLine, COPY_PROPERTY_NAMES);

     shoppingLineCommand.setId(cookieShoppingCartLine.getId());
     shoppingLineCommand.setGift(null == cookieShoppingCartLine.getIsGift() ? false : cookieShoppingCartLine.getIsGift());

     return shoppingLineCommand;
 }
}

然后调用:

public List<ShoppingCartLineCommand> load(HttpServletRequest request){
 // 获取cookie中的购物车行集合
 List<CookieShoppingCartLine> cookieShoppingCartLineList = getCookieShoppingCartLines(request);
 if (isNullOrEmpty(cookieShoppingCartLineList)){
     return null;
 }

 return CollectionsUtil.collect(cookieShoppingCartLineList, new ToShoppingCartLineCommandTransformer());
}

9.2 collect(Iterator, Transformer<? super O, ? extends T>)

循环 inputIterator,将每个元素使用 transformer 转换成新的对象,返回新的list.

示例:

场景: 一个简单的将list中的所有元素转成null

List<String> list = toList("xinge", "feilong1", "feilong2", "feilong2");

Transformer<String, Object> nullTransformer = TransformerUtils.nullTransformer();
List<Object> collect = CollectionsUtil.collect(list.iterator(), nullTransformer);
LOGGER.info(JsonUtil.format(collect, 0, 0));

返回:

[null,null,null,null]

9.3 collect(Iterable inputBeanIterable, Class outputListBeanType, String... includePropertyNames)

循环 inputBeanIterable,将每个元素使用转换程成新的 outputListBeanType 类型对象(如有需要只copy传入的 includePropertyNames 属性) 返回新的 list.示例:已知有以下两个类 User 和 Customer public class User{ // The id. private Long id = 0L; //** The name. private String name = "feilong"; //** 年龄. private Integer age; //setter /getter public User(Long id, String name){ this.id = id; this.name = name; } } public class Customer{ //** The id. private long id; //* The name. private String name; //setter /getter }此时有以下的 List<User> 需要转换成 List<Customer> List<User> list = toList(// new User(23L, "张飞"), new User(24L, "关羽"), new User(25L, "刘备"));以前你需要如此这般写: List<Customer> customerList = new ArrayList<>(); for (User user : list){ Customer customer = new Customer(); customer.setId(user.getId()); customer.setName(user.getName()); customerList.add(customer); }如果属性很多,书写代码很繁琐此时你可以这么写: List<Customer> customerList = CollectionsUtil.collect(list, Customer.class);一行代码搞定集合转换问题如果你只想转换 id 属性,你可以: List<Customer> customerList = CollectionsUtil.collect(list, Customer.class,"id");说明:outputListBeanType 需要有默认的构造函数