java8的stream流处理使用例子

数据准备

		//准备map数据
        List> mapDatas = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            Map map = new HashMap<>();
            if (i % 2 == 0){
                map.put("province","北京");
                map.put("listcount",""+i*Math.round(15f));
                map.put("index","count"+i);
            }else {
                map.put("province","上海");
                map.put("listcount",""+i*Math.round(15f));
                map.put("index","count"+i);
            }
            mapDatas.add(map);
        }

        //准备entity数据
        List studentList = new ArrayList<>();
        studentList.add(new Student("1231","典韦","男","2011-09-08","12379","刀"));
        studentList.add(new Student("1233","孙尚香","女","2012-09-08","12379","枪"));
        studentList.add(new Student("1232","李白","男","2010-09-08","12379","剑"));
        studentList.add(new Student("1234","王昭君","女","2010-09-08","12379","棍子"));

1. stream().forEach

		//1 stream().forEach的使用(对象list跟maplist是一样使用的)
        mapDatas.stream().forEach(map -> {
            System.err.println(map);
        });        

2. stream().filter

		//2 stream().filter 的用法 过滤出北京的数据
        List> filterDatas = mapDatas.stream().filter(map -> {
            return map.get("province").equals("北京");
        }).collect(Collectors.toList());
        System.err.println(filterDatas);
        结果:
        [{listcount=0, province=北京, index=count0}, {listcount=30, province=北京, index=count2}, {listcount=60, province=北京, index=count4}, {listcount=90, province=北京, index=count6}, {listcount=120, province=北京, index=count8}]

3. stream().map

		//3 stream().map 提取list对象的某个属性为list,也可以提取map的某个key
        List snames = studentList.stream().map(student -> {
            return student.getSname();
        }).collect(Collectors.toList());
        System.err.println(snames);
        结果:
        [典韦, 孙尚香, 李白, 王昭君]

4. stream().sorted

		//4 stream().sorted 根据某个属性排序
        // 升序
        // entity排序
        List sortStudents = studentList.stream()
                .sorted(Comparator.comparing(Student::getSno))
                .collect(Collectors.toList());
        System.err.println(sortStudents);
        System.err.println("-------------");

        // map 排序
        List> mapSortDatas = mapDatas.stream()
                .sorted(Comparator.comparing(map -> (map.get("index"))))
                .collect(Collectors.toList());
        System.err.println(mapSortDatas);
        System.err.println("------------------");

        //降序
        // entity排序
        List sortStudents2 = studentList.stream()
                .sorted((student1, student2) -> student2.getSno().compareTo(student1.getSno()))
                .collect(Collectors.toList());
        System.err.println(sortStudents2);
        System.err.println("-------------");

        // map 排序
        List> mapSortDatas2 = mapDatas.stream()
                .sorted((map1, map2) -> map2.get("index").compareTo(map1.get("index")))
                .collect(Collectors.toList());
        System.err.println(mapSortDatas2);
		结果:
		[Student{sno='1231', sname='典韦', sex='男', birthday='2011-09-08', phone='12379', dorm='刀'}, Student{sno='1232', sname='李白', sex='男', birthday='2010-09-08', phone='12379', dorm='剑'}, Student{sno='1233', sname='孙尚香', sex='女', birthday='2012-09-08', phone='12379', dorm='枪'}, Student{sno='1234', sname='王昭君', sex='女', birthday='2010-09-08', phone='12379', dorm='棍子'}]
		-------------
		[{listcount=0, province=北京, index=count0}, {listcount=15, province=上海, index=count1}, {listcount=30, province=北京, index=count2}, {listcount=45, province=上海, index=count3}, {listcount=60, province=北京, index=count4}, {listcount=75, province=上海, index=count5}, {listcount=90, province=北京, index=count6}, {listcount=105, province=上海, index=count7}, {listcount=120, province=北京, index=count8}, {listcount=135, province=上海, index=count9}]
		------------------
		[Student{sno='1234', sname='王昭君', sex='女', birthday='2010-09-08', phone='12379', dorm='棍子'}, Student{sno='1233', sname='孙尚香', sex='女', birthday='2012-09-08', phone='12379', dorm='枪'}, Student{sno='1232', sname='李白', sex='男', birthday='2010-09-08', phone='12379', dorm='剑'}, Student{sno='1231', sname='典韦', sex='男', birthday='2011-09-08', phone='12379', dorm='刀'}]
		-------------
		[{listcount=135, province=上海, index=count9}, {listcount=120, province=北京, index=count8}, {listcount=105, province=上海, index=count7}, {listcount=90, province=北京, index=count6}, {listcount=75, province=上海, index=count5}, {listcount=60, province=北京, index=count4}, {listcount=45, province=上海, index=count3}, {listcount=30, province=北京, index=count2}, {listcount=15, province=上海, index=count1}, {listcount=0, province=北京, index=count0}]

5. stream().collect 利用Collectors分组
   //list entity分组
   
   //list map 分组
   
   分组过后排序
   list entity 分组排序

		Map> sortGroupStudent = studentList.stream()
                .sorted(Comparator.comparing(Student::getSno))
                .collect(Collectors.groupingBy(Student::getSex));
        System.err.println(sortGroupStudent);
        结果:
        {女=[Student{sno='1233', sname='孙尚香', sex='女', birthday='2012-09-08', phone='12379', dorm='枪'}, Student{sno='1234', sname='王昭君', sex='女', birthday='2010-09-08', phone='12379', dorm='棍子'}], 男=[Student{sno='1231', sname='典韦', sex='男', birthday='2011-09-08', phone='12379', dorm='刀'}, Student{sno='1232', sname='李白', sex='男', birthday='2010-09-08', phone='12379', dorm='剑'}]}

	list map 分组排序

		Map>> sortGroupMap = mapDatas.stream().sorted(Comparator.comparing(map -> map.get("index")))
                .collect(Collectors.groupingBy(map -> (map.get("province"))));
        System.err.println(sortGroupMap);
        结果:
        {上海=[{listcount=15, province=上海, index=count1}, {listcount=45, province=上海, index=count3}, {listcount=75, province=上海, index=count5}, {listcount=105, province=上海, index=count7}, {listcount=135, province=上海, index=count9}], 北京=[{listcount=0, province=北京, index=count0}, {listcount=30, province=北京, index=count2}, {listcount=60, province=北京, index=count4}, {listcount=90, province=北京, index=count6}, {listcount=120, province=北京, index=count8}]}