How can i convert Map of Strings and Object to a Map of Strings and List

Question

I have method that should return Map<Strings, List<String>> but in the mean time my method gives me a Map<Strings, Object>, I want to transfer the values of object into a List of Strings.

Here is the current code:

    @SuppressWarnings("unchecked")
    static Map<String, List<String>> getQueryParameters(JsonObject inputJsonObject) {

        JsonArray parameters = inputJsonObject.getJsonArray("parameters");

        Optional<JsonObject> queryParameters = parameters.stream().
            filter(JsonObject.class::isInstance).
            map(JsonObject.class::cast).
            filter(jsonObject -> jsonObject.getJsonObject("queryParameters") != null).
            map(item -> item.getJsonObject("queryParameters")).findFirst();

        Map<String, Object> paramMap = queryParameters.get().getMap();

paramMap contains key and value , values could be an arrays of integers so I want to put them into the map below:

 Map<String, List<String>> mystore = new LinkedHashMap<String, List<String>>();

My solution is this which did not work correctly

 Map<String, List<String>> mystore = new LinkedHashMap<String, List<String>>();

        Map<String, Object> paramMap = queryParameters.get().getMap();

        Iterator it = paramMap.entrySet().iterator();

          while (it.hasNext()) {
            String key = it.next().toString();
            if (!mystore.containsKey(key)) ;

            mystore.put(key, new LinkedList<String>());

            mystore.get(key).add(it.next().toString());
        }

I was a key holding another key as value and is just a mix up , any suggestions? After debuging what happens i see that mystore holds both "key and value" together as a key and value it hold the next "key and value as value

Bart · Accepted Answer · 2018-07-12 07:13:39Z

2

Should be something like this:

while (it.hasNext()) {
        Map.Entry<String, Object> next = iterator.next();
        String key = next.getKey();
        Object value = next.getValue();
        if (!mystore.containsKey(key)) mystore.put(key, new LinkedList<String>());
        mystore.get(key).add(value.toString());
    }

answered Jul 12, 2018 at 7:13

Bart

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2 Comments

valik Over a year ago

iterator.nexr() need to be casted like this (Map.Entry<String, Object>) and also i think you mean it.next as was written in while statement

Bart Over a year ago

it.next returns the the next key-value entry of the map. No cast should be needed.

Karthik R · Accepted Answer · 2018-07-12 07:05:45Z

I'm not writing a program for you, but instead help you in finding a problem. You are confused with Entry. If you are using IDE, you should solve it easier. Look for this line :

String key = it.next().toString();

Entry has a K,V pair. The iterator returns an EntrySet and thus usage to get key is it.next().getKey() and it.next().getValue()

Now that you have a correct key, please go on debugging. Instead of putting and getting and manipulating in below lines of your code. Put with correct value instead?

Yours:

mystore.put(key, new LinkedList<String>());
mystore.get(key).add(it.next().toString());

What about?:

Entry entry = it.next();
//Get key and value here. DO coding using Entry's methods
List<String> ll = new LinkedList<String>();
ll.add(value)
mystore.put(key, ll);

Tip: Always have the Javadoc or reference documentation handy for knowing more. That's how you learn the language. Refer:https://docs.oracle.com/javase/7/docs/api/java/util/Map.Entry.html

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