工作记录------List转Map的六种方式Stream

1.key和value都是对象中的某个属性值.
2.key是对象中的某个属性值，value是对象本身（使用返回本身的lambda表达式）
3.key是对象中的某个属性值，value是对象本身（使用Function.identity()的简洁写法
4.key是对象中的某个属性值，value是对象本身，当key冲突时选择第二个key值覆盖第一个key值
5.key是对象中的几个值一起，value是对象本身，当key冲突时选择第二个key值覆盖第一个key值
6.key是几个属性一起，value也是几个属性一起

key和value都是对象中的某个属性值

Map collect = list.stream().collect(Collectors.toMap(PmWorkCellsDto::getColumIndex, PmWorkCellsDto::getWorkCellId));

@Testpublic void testListToMap(){List list = new ArrayList<>();for (int i = 0 ;i<5;i++){PmWorkCellsDto pmAreasT = new PmWorkCellsDto();pmAreasT.setColumIndex(i);pmAreasT.setWorkCellId(i+":value");list.add(pmAreasT);}Map collect = list.stream().collect(Collectors.toMap(PmWorkCellsDto::getColumIndex, PmWorkCellsDto::getWorkCellId));for(Map.Entry entry:collect.entrySet()){System.out.println(entry.getKey()+"--->"+entry.getValue());}}

0—>0:value
1—>1:value
2—>2:value
3—>3:value
4—>4:value

key是对象中的某个属性值，value是对象本身（使用返回本身的lambda表达式）

Map collect = list.stream().collect(Collectors.toMap(PmWorkCellsDto::getColumIndex, PmWorkCellsDto ->PmWorkCellsDto));

@Testpublic void testListToMap(){List list = new ArrayList<>();for (int i = 0 ;i<5;i++){PmWorkCellsDto pmAreasT = new PmWorkCellsDto();pmAreasT.setColumIndex(i);pmAreasT.setWorkCellId(i+":value");list.add(pmAreasT);}Map collect = list.stream().collect(Collectors.toMap(PmWorkCellsDto::getColumIndex, PmWorkCellsDto ->PmWorkCellsDto));for(Map.Entry entry:collect.entrySet()){System.out.println(entry.getKey()+"--->"+entry.getValue());}}

key是对象中的某个属性值，value是对象本身（使用Function.identity()的简洁写法

 @Testpublic void testListToMap(){List list = new ArrayList<>();for (int i = 0 ;i<5;i++){PmWorkCellsDto pmAreasT = new PmWorkCellsDto();pmAreasT.setColumIndex(i);pmAreasT.setWorkCellId(i+":value");list.add(pmAreasT);}Map collect = list.stream().collect(Collectors.toMap(PmWorkCellsDto::getColumIndex,  Function.identity()));for(Map.Entry entry:collect.entrySet()){System.out.println(entry.getKey()+"--->"+entry.getValue());}}

key是对象中的某个属性值，value是对象本身，当key冲突时选择第二个key值覆盖第一个key值

Map collect = list.stream().collect(Collectors.toMap(PmWorkCellsDto::getColumIndex, Function.identity(),(oldValue, newValue) -> newValue));

@Testpublic void testListToMap(){List list = new ArrayList<>();for (int i = 0 ;i<5;i++){PmWorkCellsDto pmAreasT = new PmWorkCellsDto();pmAreasT.setColumIndex(i);pmAreasT.setWorkCellId(i+":value");list.add(pmAreasT);}Map collect = list.stream().collect(Collectors.toMap(PmWorkCellsDto::getColumIndex,  Function.identity(),(oldValue, newValue) -> newValue));for(Map.Entry entry:collect.entrySet()){System.out.println(entry.getKey()+"--->"+entry.getValue());}}

key是对象中的几个值一起，value是对象本身，当key冲突时选择第二个key值覆盖第一个key值

Map collect = list.stream().collect(Collectors.toMap(x->{
return x.getColumIndex()+x.getWorkCellId();
}, Function.identity(),(oldValue, newValue) -> newValue));

 @Testpublic void testListToMap(){List list = new ArrayList<>();for (int i = 0 ;i<5;i++){PmWorkCellsDto pmAreasT = new PmWorkCellsDto();pmAreasT.setColumIndex(i);pmAreasT.setWorkCellId(i+":value");list.add(pmAreasT);}Map collect = list.stream().collect(Collectors.toMap(x->{return x.getColumIndex()+x.getWorkCellId();},  Function.identity(),(oldValue, newValue) -> newValue));for(Map.Entry entry:collect.entrySet()){System.out.println(entry.getKey()+"--->"+entry.getValue());}}

同理如果想要key是几个属性一起，value也是几个属性一起

Map collect = list.stream().collect(Collectors.toMap(x->{
return x.getColumIndex()+x.getWorkCellId();
}, y->{
return y.getColumIndex()+y.getWorkCellId();
},(oldValue, newValue) -> newValue));

@Testpublic void testListToMap(){List list = new ArrayList<>();for (int i = 0 ;i<5;i++){PmWorkCellsDto pmAreasT = new PmWorkCellsDto();pmAreasT.setColumIndex(i);pmAreasT.setWorkCellId(i+":value");list.add(pmAreasT);}Map collect = list.stream().collect(Collectors.toMap(x->{return x.getColumIndex()+x.getWorkCellId();},  y->{return y.getColumIndex()+y.getWorkCellId();},(oldValue, newValue) -> newValue));for(Map.Entry entry:collect.entrySet()){System.out.println(entry.getKey()+"--->"+entry.getValue());}}