集合分组工具类

电玩女神 2023-10-04 10:11 31阅读 0赞

### 自定义分组 ###

/**
     * 集合分组工具类
     *
     * @autor WYH
     */
    public class GroupUtils {
        
    
        /**
         * 集合分组算法封装。
         *
         * @param colls 待分组的集合
         * @param gb    分组依据
         * @return Map<T, List < E>>
         */
        public static final <T extends Comparable<T>, E> Map<T, List<E>> group(Collection<E> colls, GroupBy<T> gb) {
        
    
            if (colls == null || colls.isEmpty()) {
         // 分组集合为空
                return null;
            }
            if (gb == null) {
        // 分组依据为空
                return null;
            }
            Map<T, List<E>> map = new HashMap<T, List<E>>();
            Iterator<E> it = colls.iterator();
            while (it.hasNext()) {
        
                E e = it.next();
                T t = gb.groupby(e);
                if (map.containsKey(t)) {
        
                    map.get(t).add(e);
                } else {
        
                    List<E> list = new ArrayList<E>();
                    list.add(e);
                    map.put(t, list);
                }
            }
            return map;
        }
    
        /**
         * 返回空数据
         *
         * @param colls
         * @param gb
         * @param <T>
         * @param <E>
         * @return
         */
        public static <T extends Comparable<T>, E> Map<T, List<E>> groupNew(Collection<E> colls, GroupBy<T> gb) {
        
    
            if (colls == null || colls.isEmpty()) {
         // 分组集合为空
                return new HashMap<>();
            }
            if (gb == null) {
        // 分组依据为空
                return new HashMap<>();
            }
            Map<T, List<E>> map = new HashMap<T, List<E>>();
            Iterator<E> it = colls.iterator();
            while (it.hasNext()) {
        
                E e = it.next();
                T t = gb.groupby(e);
                if (map.containsKey(t)) {
        
                    map.get(t).add(e);
                } else {
        
                    List<E> list = new ArrayList<E>();
                    list.add(e);
                    map.put(t, list);
                }
            }
            return map;
        }
    }

/**
     * 分组依据接口
     *
     * @autor WYH
     * @since 2019-08-22
     */
    public interface GroupBy<T> {
        
    
        T groupby(Object obj);
    }

测试

public class GroupTest {
        
    
        public static void main(String[] args) {
        
    
            Map<String, String> map = new HashMap<>();
            map.put("name","张三");
            map.put("age","20");
            map.put("dept","开发");
            Map<String, String> map1 = new HashMap<>();
            map1.put("name","李四");
            map1.put("age","21");
            map1.put("dept","人事");
            Map<String, String> map2 = new HashMap<>();
            map2.put("name","王五");
            map2.put("age","22");
            map2.put("dept","行政");
            Map<String, String> map3 = new HashMap<>();
            map3.put("name","米卡");
            map3.put("age","22");
            map3.put("dept","人事");
    
            List<Map<String, String>> list = new ArrayList<>();
            list.add(map);
            list.add(map1);
            list.add(map2);
            list.add(map3);
            // 将数据分组
            Map<String, List<Map<String, String>>> group = GroupUtils.group(list, new GroupBy<String>() {
        
                @Override
                public String groupby(Object obj) {
        
                    if (obj instanceof Map) {
        
                        Map<String, String> map = (Map<String, String>) obj;
                        return (String) map.get("age");
                    }
                    return null;
                }
            });
            System.out.println(group);
        }
    }

打印结果：

{22=[{name=王五, dept=行政, age=22}, {name=米卡, dept=人事, age=22}], 20=[{name=张三, dept=开发, age=20}], 21=[{name=李四, dept=人事, age=21}]}

### Java8 ###

//按照多个属性分组，key为多个属性合
    Map<String, List<Map<String, String>>> collect = list.stream().collect(Collectors.groupingBy(e -> e.get("dept") + e.get("age")));
    System.out.println(collect);
    //按照多个属性分组，key为单个属性合
    Map<String, Map<String, List<Map<String, String>>>> result = list.stream().collect(Collectors.groupingBy(e -> e.get("dept"), Collectors.groupingBy(e -> e.get("age"))));
    System.out.println(result);