Question 121556 in Redis Question posted in
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Redis – Java Merge 2 HashMap without null values

I know that this question has been already posted. But after many days searching a solution, i can’t find one..

I have two objects, which are converted to HashMap.
Once these HashMap I need to merge object 1 into object 2.
Namely: These objects can contain null keys.

I want the attribute of object 1 to replace the attribute of object 2 only if the attribute of object 1 is not null.


private <T> Map<String, T> mergeObjects(T first, T second) {
        ObjectMapper oMapper = new ObjectMapper();

        // On transforme l'objet en une MAP afin de faciliter le merge
        Map<String, T> objet1Map = oMapper.convertValue(first, Map.class);
        Map<String, T> objet2Map = oMapper.convertValue(second, Map.class);


        // Merge object 1 into object 2 (but it merges null values, i don't want that..)
        objet2Map.putAll(objet1Map);

        return objet2Map;
    }

My object is something like that :

{
        "environment": "d",
        "type": "deploymentconfig",
        "component": {
            "template": "redis-template.yaml",
            "routes": null,
            "parameters": {
                "REQUESTS_CPU": "25m",
                "LIMITS_MEMORY": null,
                "PROBE_PATH": null,
                "IMAGE_STREAM": "my-image",
                "IMAGE_STREAM_TAG": "6.9.6"
}
...
...
}

Edit 1 :

objet1 : {component={template=redis-pvc-component-template.yaml, parameters={REQUESTS_CPU=25m, IMAGE_STREAM=redis-5-rhel7-gtec, IMAGE_STREAM_TAG=5.16_19.12, MEMORY_LIMIT=298Mi}}, type=deploymentconfig}

objet2: {component={parameters={STORAGECLASS=prod}}, environment=p, type=deploymentconfig}

Result ->

{
        "environment": "p",
        "type": "deploymentconfig",
        "component": {
            "template": null,
            "routes": null,
            "parameters": {
                "REQUESTS_CPU": null, // disappeared
                "LIMITS_MEMORY": null,
                "PROBE_PATH": null,
                "IMAGE_STREAM": null, // disappeared
                "IMAGE_STREAM_TAG": null, // disappeared
                "MEMORY_LIMIT": null, // disappeared
                "STORAGECLASS": "prod",
                "VOLUME": null,
                "ROUTE_HOSTNAME": null,
                "IMAGE_STREAM_PROJECT": null,
                "LIVENESS_PROBE_PATH": null,
                "LIVENESS_PROBE_DELAY": null,
                "READINESS_PROBE_PATH": null,
                "READINESS_PROBE_DELAY": null,
                "JAVA_OPTIONS": null,
                "ENVIRONMENT": null
            }
        },
        "autoscaler": null
    }

As you can see many properties have disappeared after the putAll..

Tags:

3

Answers


  1. Chosen as BEST ANSWER
    0

    Answer that works for me : -> https://stackoverflow.com/a/29698326/13761574

    // This is fancier than Map.putAll(Map)
private static Map deepMerge(Map original, Map newMap) {
    for (Object key : newMap.keySet()) {
        if (newMap.get(key) instanceof Map && original.get(key) instanceof Map) {
            Map originalChild = (Map) original.get(key);
            Map newChild = (Map) newMap.get(key);
            original.put(key, deepMerge(originalChild, newChild));
        } else if (newMap.get(key) instanceof List && original.get(key) instanceof List) {
            List originalChild = (List) original.get(key);
            List newChild = (List) newMap.get(key);
            for (Object each : newChild) {
                if (!originalChild.contains(each)) {
                    originalChild.add(each);
                }
            }
        } else {
            original.put(key, newMap.get(key));
        }
    }
    return original;
}

  2. 0

    Edit 1:

        @Test
    public void test() throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.setSerializationInclusion(Include.NON_NULL);

        HashMap<String,String> map = new HashMap<>();

        map.put("some","some");
        map.put("other",null);

        HashMap<String,Object> othermap = new HashMap<>();
        othermap.put("keey","value");
        othermap.put("nested",map);

        final String asString = objectMapper.writeValueAsString(othermap);
        System.out.println(asString);
    }
}

    without serialization config.

    {"keey":"value","nested":{"some":"some","other":null}}.

    with serialization config.

    {"keey":"value","nested":{"some":"some"}} //non null inclusion.

    Can you try setting objectmapper to exclude null properties?

    mapper.setSerializationInclusion(Include.NON_NULL);

    https://www.baeldung.com/jackson-ignore-null-fields#globally

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  3. 0

    You’ll need to merge the individual entries of the maps.

    If you just want to keep the value of the first map, you can just use putIfAbsent().

    Map<String, T> map1 = ...
Map<String, T> map2 = ...
Map<String, T> result = new HashMap<>(map1);

map2.forEach((key, value) -> result.putIfAbsent(key, value);

    If you have the value in both maps, you can use merge to define behavior to calculate what value you want.

    map2.forEach((key, value) -> result.merge(key, value, // put if absent
   (v1, v2) -> v1); // calculate new value if present in both
}

    The latter example I give behaves equivalent to the first, ie it keeps the existing value in the map.

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