如何通过将其中一个值切换为键来创建 HashMap 的 HashMap

Question

I have a map of maps as follows:- myMap = {cfds2={fname=ck1, uname=jk1, tenant=ABC1}, cfds1={fname=ck, uname=jk, tenant=ABC}} and expecting a returned map as :- {tenant={fname=ck, handler=cfds1, uname=jk, tenant=ABC}} when getIoiProperties(String tenant) is being called with ABC . So Create a new map by using one of the key of the inner map to be key of a newly created map and key of the outer map becomes one of the values.

import com.google.common.collect.Maps;
import java.util.Map;

public class MapTest
{
   public Map<String, Map<String, String>> getIoiProperties(String tenant) 
  {
    Map<String, String> tenantMap = Maps.newHashMap();
    tenantMap.put("tenant", "ABC");
    tenantMap.put("uname", "jk");
    tenantMap.put("fname", "ck");
    //Map of Maps
    Map<String, Map<String, String>> myMap = Maps.newHashMap();
    myMap.put("cfds1", tenantMap);

    Map<String, String> tenantMap1 = Maps.newHashMap();
    tenantMap1.put("tenant", "ABC1");
    tenantMap1.put("uname", "jk1");
    tenantMap1.put("fname", "ck1");

    myMap.put("cfds2", tenantMap1);

    System.out.println("myMap = " + myMap);

    Map<String, Map<String, String>> result = Maps.newHashMap();
    //iterate map
    for (Map.Entry<String, Map<String, String>> entry : myMap.entrySet()) {
        String key = entry.getKey();
        for (Map.Entry<String, String> entry1 : entry.getValue().entrySet())
            if (entry1.getKey().equals("tenant") && entry1.getValue().equals(tenant)) {
                entry.getValue().put("handler", key);
                result.put(entry1.getKey(), entry.getValue());
            }
    }

    System.out.println(result);
    System.out.println("myMap = " + myMap);
    return result;
}

public static void main(String[] args) {
    MapTest mp = new MapTest();
    Map<String, Map<String, String>> res = mp.getIoiProperties("ABC");
    System.out.println(res.get("tenant"));
}

}

Answer 1

Before reading my algorithm, note that I did not check if the conditionals in the for loops work properly, that is on you. However, if they are alright, it should work perfectly.

Map<String, Map<String, String>> result = Maps.newHashMap();

for (Map.Entry<String, Map<String, String>> entry : myMap.entrySet()) {
    Map<String, String> handlerMap = Maps.newHashMap();
    handlerMap.put("handler", entry.getKey());
    boolean save = false;

    for (Map.Entry<String, String> entry1 : entry.getValue().entrySet())
        if (entry1.getKey().equals("tenant")){
            if (entry1.getValue().equals(tenant){
                save = true;
            }
        }
        handlerMap.put(entry1.getKey(), entry1.getValue());   
    }
    if (save){
        result.put("tenant", handlerMap);
        breaK; // Since there is just 1 tenant x handler, I stop the loop
    }
 }

Answer 2

Please check the below code

public Map<String, Map<String, String>> getIoiProperties(String tenant)
    {
        Map<String, String> tenantMap = new HashMap<>();
        tenantMap.put("tenant", "ABC");
        tenantMap.put("uname", "jk");
        tenantMap.put("fname", "ck");
        //Map of Maps
        Map<String, Map<String, String>> myMap =new HashMap<>();
        myMap.put("cfds1", tenantMap);

        Map<String, String> tenantMap1 = new HashMap<>();
        tenantMap1.put("tenant", "ABC1");
        tenantMap1.put("uname", "jk1");
        tenantMap1.put("fname", "ck1");

        myMap.put("cfds2", tenantMap1);

        System.out.println("myMap = " + myMap);

        Map<String, Map<String, String>> result = new HashMap<>();
        //iterate map
        for (Map.Entry<String, Map<String, String>> entry : myMap.entrySet()) {
            String key = entry.getKey();
            for (Map.Entry<String, String> entry1 : entry.getValue().entrySet())
                if (entry1.getKey().equals("tenant") && entry1.getValue().equals(tenant)) {
                    entry.getValue().put("handler", key);
                    result.put(entry1.getValue(), entry.getValue());
                    result.get(tenant).remove("tenant");
                }
        }

        System.out.println(result);
        //System.out.println("myMap = " + myMap);
        return result;
    }

Two issues were there in your code

1. "tenant" key not removed from the inner map

2. Instead of result.put(entry1.getKey(), entry.getValue()); result.put(entry1.getValue(), entry.getValue()); should be used.

Answer 3

As you said, the previous code by dassum worked. Based on that, I decided to improve it to try to make it work. So, what is happening is that entry.getValue().put("handler", key); cannot be done while iterating. You can't modify the entry, as another thread is iterating over it; which throws the ConcurrentModificationException . So here's a way to solve it, I reused some of the code proportioned by erickson . What I did is create another map outside the loop to store the data that will be returned. Then, I merge both the previous and stored data. I hope this time it works.

 public Map<String, Map<String, String>> getIoiProperties(String tenant)
{
    Map<String, String> tenantMap = new HashMap<>();
    tenantMap.put("tenant", "ABC");
    tenantMap.put("uname", "jk");
    tenantMap.put("fname", "ck");
    //Map of Maps
    Map<String, Map<String, String>> myMap =new HashMap<>();
    Map<String, Map<String, String>> store =new HashMap<>();
    myMap.put("cfds1", tenantMap);

    Map<String, String> tenantMap1 = new HashMap<>();
    tenantMap1.put("tenant", "ABC1");
    tenantMap1.put("uname", "jk1");
    tenantMap1.put("fname", "ck1");

    myMap.put("cfds2", tenantMap1);

    System.out.println("myMap = " + myMap);

    Map<String, Map<String, String>> result = new HashMap<>();
    //iterate map
    for (Map.Entry<String, Map<String, String>> entry : myMap.entrySet()) {
        String key = entry.getKey();
        for (Map.Entry<String, String> entry1 : entry.getValue().entrySet())
            if (entry1.getKey().equals("tenant") && entry1.getValue().equals(tenant)) {
                store.put("handler", key);
                result.put(entry1.getValue(), entry.getValue());
                result.get(tenant).remove("tenant");
            }
    }
    Map<String, Map<String, String>> tmp =new HashMap<>(store);
    tmp.keySet().removeAll(result.keySet());
    result.putAll(tmp);
    store.forEach(target::putIfAbsent);

    System.out.println(result);
    //System.out.println("myMap = " + myMap);
    return result;
}