CODEWITHSUNDEEP
jsonspring-mvcjackson
genxgeek
genxgeek

Reputation: 13367

Json jackson mapping ask

How can I map the following json payload to a more friendly dictionary like look up? The data I get back is coming back as generic key values in a list. But I want to be able to access everything as a dictionary lookup by the key instead of storing everything as a list.

[
   {
      "key":"value1",
      "values":[
         10.5
      ]
   },
   {
      "key":"value2",
      "values":[
         20.5
      ]
   }
   o o o more values here... o o o
]

This is what I have for object to map but I want to map by key to automatically building a hashmap or dictionary withough having to iterate thought the list. 

class keyValPairObject {
    private String key;
    private List<?> values;
}

class mainMapper {
    List<keyValPairObject> theKeyValPairValues;
}

I'd like to store it in an object where I can access it like:

 theKeyValPairValues["values1"].values;

Upvotes: 1

Views: 276

Answers (2)

WalkerDev
WalkerDev

Reputation: 1322

Okay I hope this helps you. Here is some code:

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.codehaus.jackson.map.ObjectMapper;

public String hashmapToJson() {

    ObjectMapper mapper = new ObjectMapper();
    String result = "";

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

    String key1 = "values1";
    String key2 = "values2";
    String key3 = "values3";

    List<String> list1 = new ArrayList<String>();
    List<String> list2 = new ArrayList<String>();
    List<String> list3 = new ArrayList<String>();

    for(int i = 0; i < 3; i++){
        list1.add("Element" + i);
        list2.add("Element" + i);
        list3.add("Element" + i);
    }

    map.put(key1, list1);
    map.put(key2, list2);
    map.put(key3, list3);

    try {
        result = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(map);
    } catch (IOException e) {
        e.printStackTrace();
    }

    return result;

}

This will return:

{
 "values1":["Element0","Element1","Element2"],
 "values2":["Element0","Element1","Element2"],
 "values3":["Element0","Element1","Element2"]
}

Is this what you were looking for?

Upvotes: 1

StaxMan
StaxMan

Reputation: 116620

Perhaps you should use "Tree Models", so that:

JsonNode root = mapper.readTree(jsonSource);

and then you can traverse values using "get()" and "path()" methods. path() is nice since you can skip any null checks (if a node does not exist, a virtual "missing" node is included, so you can freely chain calls).

That way you would do like:

int value = rootNode.path(0).path("value").path(0).asIntValue();

to get that 10.5 value from your structure.

Bit more info can be found from this entry and from "Tree Model" of databind project's readme.

Upvotes: 1

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