I have a List of inputs which has to be converted into a defined format in Java

Question

Not sure about the best way to get this List in below format. Please suggest better way to get this format in Java. And also below list is dynamic. Sometimes the values can go up to 10 or more

List<String> list = Arrays.asList("ABC", "DEF", "GHI");

Now we want the above list to be printed as below -

[{"key" : "ABC"}, {"key" : "DEF"}, {"key" : "GHI"}]

I tried to use MultiMap like below

Multimap<String, String> multimap = ArrayListMultimap.create();

multimap.put("key", "ABC");
multimap.put("key", "DEF");
multimap.put("key", "GHI");

Which prints values like

{key=[ABC, DEF, GHI]}

Yes. I used MultiMap not Map. if you have any other sugesstion, you are welcome. Thank you. — hdevi, Jan 19 '20 at 05:45
If it's just a question of *printing* the way you showed, then you can try `System.out.println(multimap.entries().stream().map(e -> String.format("{\"%s\": \"%s\"}", e.getKey(), e.getValue())).collect(Collectors.toList()));` — ernest_k, Jan 19 '20 at 05:52
@ernest_k This looks great. In this case, Can I also Just format the List instead of going for MultiMap again ? I mean the List list = Arrays.asList("ABC", "DEF", "GHI"); as in the same format with 'Key' as same for the values in the list — hdevi, Jan 19 '20 at 05:56
Will it always be the same key for each element of the list (such that you can hard-code it there)? — ernest_k, Jan 19 '20 at 05:58
@ernest_k Yes. the Key value is same. Hardcoding is also fine. But in the above example, you are using map. Can we just use for List and get the same format ? — hdevi, Jan 19 '20 at 05:59
Sure, you can `list.stream().map(e -> String.format("{\"key\" : \"%s\"}", e)).collect(Collectors.toList())` — ernest_k, Jan 19 '20 at 06:02
@ernest_k I see an error as 'Incompatible types. Required String but, 'collect' was inferred to R: no instance(s) of type variables(s) T exits so that List confirms to String.' — hdevi, Jan 19 '20 at 06:12
@hdevi `list.stream().map(e -> String.format("{\"key\" : \"%s\"}", e)).collect(Collectors.toList()).toString(); ` You need to convert it to `String` using `toString()` — Govinda Sakhare, Jan 19 '20 at 06:35

Govinda Sakhare · Answer 1 · 2020-01-19T06:37:04.690

You can access underlying entries structure multimap.entries() and format the string as per the need.

multimap.entries().stream()
      .map(entry -> String.format("{\"%s\": \"%s\"}", entry.getKey(), entry.getValue()))
      .collect(Collectors.toList()));

ernest_k has already provided a couple of nice ways to get the desired string in the comment section. You can extend those solutions by writing a custom class that can take a key.

List<String> list = Arrays.asList("ABC", "DEF", "GHI");
MapKeyToValues keyValues = new MapKeyToValues("key", list); // change key as per your need
System.out.println(keyValues);
String formattedString = keyValues.toString();

Custom converter class.

public class MapKeyToValues {
    private final String key;
    private final List<String> list;

    public MapKeyToValues(String key, List< String > list) {
        this.key = key;
        this.list = list;
    }

    @Override
    public String toString( ) {
       // need to handle null cases here
       return list.stream()
                .map(value -> String.format("{\"%s\" : \"%s\"}", key, value))
                .collect(Collectors.toList()).toString();
    }
}

score 0 · Answer 2 · answered Jan 19 '20 at 06:11

0

String are immutable. So you have to set again in the list the value. Try this one.

List<String> list = Arrays.asList("ABC", "DEF", "GHI");
for(int i = 0; i < list.size();i++){                  
    list.set(i,"{\"key\" : \""+list.get(i)+"\"}");
}

answered Jan 19 '20 at 06:11

Abdul Alim Shakir

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I have a List of inputs which has to be converted into a defined format in Java

2 Answers2