Merge arraylist of maps in json, java

Question

I have 2 arraylists(of same size) in json as below:

List<HashMap<String, String>> list1 = new Arraylist<HashMap<String, String>>();

List<HashMap<String, String>> list2 = new Arraylist<HashMap<String, String>>();

I want to merge the above lists into a single one.

For ex:

List1:

[{ " key1": "value1", " key2": "value2"}, 
{ " key11": "value11", " key22": "value22"}]

List2:

[{ " key3": "value3"},{" key33": "value33"}]

Expected output:

[{ " key1": "value1", " key2": "value2", " key3": "value3"}, 
{ " key11": "value11", " key22": "value22", " key3": "value3"}]

An early response will be highly appreciated. Thanks a lot in advance.

What is your original input? Are these the JSON values or the Java POJOs? — fge
– fge, Commented Apr 8, 2016 at 6:12
Original input are the lists that I want to merge and are json values — learner
– learner, Commented Apr 8, 2016 at 6:15

Wakachopo · Accepted Answer · 2016-04-08 06:11:35Z

2

If the two ArrayList have the same type (they seem to be arraylist of maps):

 list1.addAll(list2)

answered Apr 8, 2016 at 6:11

Wakachopo

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1 Comment

learner Over a year ago

Thanks for your response. list1.addAll(list2) gives the following O/p: [{{ " key1": "value1", " key2": "value2"},{ " key3": "value3"}}, {{ " key11": "value11", " key22": "value22"},{ " key3": "value3"}}]

Eric Wei · Accepted Answer · 2016-04-08 06:38:44Z

1

Your expected output probably be:

[{ " key1": "value1", " key2": "value2", " key3": "value3"}, { " key11": "value11", " key22": "value22", " key33": "value33"}]

You didn't indicate whether two lists had same size or not. According to your example, I assumed the lists had same size. So the code could be like below:

for (int i = 0; i < list1.size(); i++) {
  list1.get(i).putAll(list2.get(i));
}

answered Apr 8, 2016 at 6:38

Eric Wei

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1 Comment

learner Over a year ago

Superb!! Thanks a tonne. This is what i was looking for. I will edit the question to mention about the same size.

Abi · Accepted Answer · 2016-04-08 06:56:50Z

0

You Just have to retrieve the Hashmap from the individual Lists and then merge them all together

for eg

HashMap m = new HashMap();
        m.put("key1", "val1");
        m.put("key2", "val2");

        HashMap m1 = new HashMap();
        m1.put("key3", "val3");
HashMap mergeMap = new HashMap();
        mergeMap.putAll(m);
        mergeMap.putAll(m1);

        System.out.println("Map:" + mergeMap);

Output

Map:{key3=val3, key2=val2, key1=val1}

answered Apr 8, 2016 at 6:56

Abi

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Comments

Muhammad Suleman · Accepted Answer · 2016-04-08 07:00:59Z

0

Edit: you can do like this

    for (HashMap<String, String> m : list2) {
        HashMap<String, String> t = list1.get(list2.indexOf(m));
        for(String key: t.keySet()){
            m.put(key, t.get(key));
        }
    }

Now Merged items are in list2.

edited Apr 8, 2016 at 7:00

answered Apr 8, 2016 at 6:15

Muhammad Suleman

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5 Comments

learner Over a year ago

Thanks for your response. list1.addAll(list2) doesnt give the expected O/p i.e. it gives: [{{ " key1": "value1", " key2": "value2"},{ " key3": "value3"}}, {{ " key11": "value11", " key22": "value22"},{ " key3": "value3"}}]

Muhammad Suleman Over a year ago

I have checked, the correct json is : [{" key1":"value1"," key2":"value2"},{" key3":"value3"},{" key11":"value11"," key22":"value22"},{" key3":"value3"}] your json is invalid in 1st place

[{{ " key1": "value1", " key2": "value2"},{ " key3": "value3"}}, {{ " key11": "value11", " key22": "value22"},{ " key3": "value3"}}]

how you have got this wrong one ?

learner Over a year ago

Sorry if I was not clear. As you have noted, after doing list1.addAll(list2)... O/P is [{" key1":"value1"," key2":"value2"},{" key3":"value3"},{" key11":"value11"," key22":"value22"},{" key3":"value3"}]. However as stated in the question, the O/P I need is: [{ " key1": "value1", " key2": "value2", " key3": "value3"}, { " key11": "value11", " key22": "value22", " key3": "value3"}]

Muhammad Suleman Over a year ago

Ahh, I got it you want to merge objects rather lists. I guess there is no built in method for this you have to write it on your own.

Muhammad Suleman Over a year ago

See my Edit on answer i wrote code for you :) which generate json of yours [{" key1":"value1"," key2":"value2"," key3":"value3"},{" key11":"value11"," key22":"value22"," key3":"value3"}]

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