Reading nested json file with ObjectMapper

Question

I am trying to read a json file (schools.json) with the help of ObjectMapper. File structure of json was something like this:

[
  {
    "schoolid": "X",
    "schoolname": "ABC",
    "schoolbranch": "DEF",
  },
 {
    "schoolid": "Y",
    "schoolname": "GDF",
    "schoolbranch": "HJG",
  },
]

And this json file was read from java like below:

static final String fileName = "schools.json";

     InputStream iStream = getClass().getClassLoader().getResourceAsStream(fileName);
          schools = objectMapper.readValue(iStream,
                  objectMapper.getTypeFactory().constructCollectionType(List.class, School.class));

Now I updated the json like this:

 [
      {
        "schoolid": "X",
        "schoolname": [{"original": "dfs"},{"translated":  "sfds"}],
        "schoolbranch":  [{"sub": "fdsf5"},{"major": "908fds"}],
      },
     {
        "schoolid": "Y",
        "schoolname": [{"original": "wera"},{"translated":  "sfds"}],
        "schoolbranch":  [{"sub": "mohk"},{"major": "908fds"}],
      },
 ]

Thus School.java is also changed. In previous version every field was a String field. Now schoolname and schoolbranch are other models/objects having fields original,translated etc.

public class School {
private int schoolid;
private SchoolName schoolname;
private SchoolBranch schoolbranch;
... 
// getters and setters here
}

And for example SchoolName.java:

public class SchoolName {
private String original;
private String translated;
// etc.
}

Now, the above java code block is not working. schools object returns null.

I could not make this work. I found some examples where json field is containing array but I could not apply a similar logic for my case. Help is appreciated.

schoolname and schoolbranch should be arrays and not objects. — Smutje
– Smutje, Commented Mar 25, 2020 at 8:47
Either change schoolname and schoolbranch to List/Array in java model, or change your json to "schoolname": {"original": "dfs","translated": "sfds"}, — Smile
– Smile, Commented Mar 25, 2020 at 8:49

MinhazMurks · Accepted Answer · 2020-03-26 05:19:02Z

1

As Smutje and Smile said, your json objects are lists not single objects. Change your java School object to:

public class School {
private int schoolid;
private List<SchoolName> schoolname;
private List<SchoolBranch> schoolbranch;
... 
// getters and setters here
}

answered Mar 26, 2020 at 5:19

MinhazMurks

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