Processing Json stored as a HashMap with multiple elements stored in values

Question

I have a json document with multiple objects. I have managed to print this out as a map but I want to be able to access elements within the values.

I can print the Map, but want to be able to print specific elements within the keys

for (Map.Entry<String,Object> entry : myMap.entrySet()) {
        System.out.println("Key: "+entry.getKey() + " Value: "+entry.getValue());
    }

This outputs the following:

Key: header1 Value: {id=123456, contents=[cat,dog,hamster]}
Key: header2 Value: {id=234567, contents=[spoon,knife,fork]}

I would like to be able to loop through and on each iteration assign id to a string and contents to a list

What have you tried so far. Sounds like homework and is too broad. — Nicholas K
– Nicholas K, Commented Jan 24, 2019 at 9:42
Sadly I am a bit old for homework! My issue is I'm not really sure if what I'm asking is possible with the data structure without using a split or something equally bodged! I am trying to access with something like myMap.get("contents") but this doesn't work and I'm not really sure what sort of thing I should be looking up with regards to the syntax — Ben
– Ben, Commented Jan 24, 2019 at 10:07

Radoslav Mitev · Accepted Answer · 2019-01-24 10:06:46Z

1

The easiest solution is to make a Class, which represents the JSON. For you, it will be like this:

public class Contents {
    private int id;
    private List<String> contents;

    //No arguments constructor, getters and setters for every field
    //You can make with @JsonCreator, too. Read Jackson documentation
};

Then you just read it as object using Jackson's ObjectMapper:

ObjectMapper mapper = new ObjectMapper();
Contents result = mapper.readValue(entry.getValue(), Contents.class);

After, this you can do whatever you like with the object. Later, you can even write it to File/Stream etc.

answered Jan 24, 2019 at 10:06

Radoslav Mitev

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Comments

Ben · Accepted Answer · 2019-01-24 12:43:56Z

0

I had a couple of issues with code I had assume to be working but have solved this now with a little help from a colleague.

value.getContents();

Was the thing I was looking for!

answered Jan 24, 2019 at 12:43

Ben

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