如何使用Java流过滤地图地图

问题描述

如何使用java流过滤地图。我可以使用双循环来做到这一点，但我认为这样做效率不高。

public class MapUsage {
    static Map> parentMap = new HashMap();
    static Map userRole = new HashMap();

    public static void main(String ... args){
        initializeData();
        displayMapForUser("user1", parentMap);
//        printMap(parentMap);

    }


    private static void displayMapForUser(String user1, Map> parentMap) {
        Integer role = new Integer(userRole.get(user1));
        Map> userMap = new HashMap();
        Map childMap = new HashMap();
        for(Map.Entry> entry : parentMap.entrySet()){
            for(Map.Entry entry1: entry.getValue().entrySet()){
                if(entry1.getKey().equals(role))
                    childMap.put(entry1.getKey(), entry1.getValue());
            }
            userMap.put(entry.getKey(), childMap);
        }
        printMap(userMap);
    }

    private static void printMap(Map> parentMap) {
        for(Map.Entry > entry: parentMap.entrySet()){
            System.out.println("key: "+entry.getKey());
            System.out.println("value: "+entry.getValue());
        }
    }

    private static void initializeData() {
        Map childMap1 = new HashMap();
        Map childMap2 = new HashMap();
        userRole.put("user1", "1");
        userRole.put("user2", "2");
        userRole.put("user3", "3");
        userRole.put("user4", "4");

        childMap1.put(1, "one");
        childMap1.put(2, "two");
        childMap1.put(3, "three");
        childMap1.put(4, "four");
        parentMap.put(1, childMap1);

        childMap2.put(1, "one");
        childMap2.put(2, "two");
        childMap2.put(3, "three");
        parentMap.put(2, childMap2);
    }
}

输出为：

key: 1
value: {1=one}
key: 2
value: {1=one}

思路：

您可以在此处使用Collectors.toMap：