JSON - Check if an array exists

Question

I have a JSON file filled with some arrays. I was wondering if anyone knows how i can check if a specifik array exists in the file.

EDIT: This is how my file is organized.

           {
                   'Objects':
                    {
                             'array1':
                              [
                                         {
                                         'element1': 'value',
                                         'element1': 'value',                                                   
                                         'element1': 'value'
                                         }
                             ],
                             // more arrays. 
                   }

I want to search through the arrays and check if a specifik array exists or not. If it doese then I will serialize it. }

Thanks in advance for all help

Answer 1

Following is an example of an approach you could take using Jackson. It uses the same JSON structure presented in the latest question updates, along with a matching Java data structure. This allows for very easy deserialization, with just one line of code.

I chose to just deserialize the JSON array to a Java List. It's very easy to change this to use a Java array instead.

(Note that there are issues with this JSON structure that I suggest changing, if it's in your control to change it.)

input.json:

{
    "objects": {
        "array1": [
            {
                "element1": "value1",
                "element2": "value2",
                "element3": "value3"
            }
        ],
        "array2": [
            {
                "element1": "value1",
                "element2": "value2",
                "element3": "value3"
            }
        ],
        "array3": [
            {
                "element1": "value1",
                "element2": "value2",
                "element3": "value3"
            }
        ]
    }
}

Java Code:

import java.io.File;
import java.util.List;
import java.util.Map;

import org.codehaus.jackson.annotate.JsonAutoDetect.Visibility;
import org.codehaus.jackson.map.ObjectMapper;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    ObjectMapper mapper = new ObjectMapper();
    // configure Jackson to access non-public fields
    mapper.setVisibilityChecker(mapper.getVisibilityChecker().withFieldVisibility(Visibility.ANY));

    // deserialize JSON to instance of Thing
    Thing thing = mapper.readValue(new File("input.json"), Thing.class);

    // look for the target named array2
    if (thing.objects.containsKey("array2"))
    {
      // an element with the target name is present, make sure it's a list/array
      if (thing.objects.get("array2") instanceof List)
      {
        // found it
        List<OtherThing> target = thing.objects.get("array2");
        OtherThing otherThing = target.get(0);
        System.out.println(otherThing.element1); // value1
        System.out.println(otherThing.element2); // value2
        System.out.println(otherThing.element3); // value3
      }
      // else do something
    }
    // else do something
  }
}

class Thing
{
  Map<String, List<OtherThing>> objects;
}

class OtherThing
{
  String element1;
  String element2;
  String element3;
}

Answer 2

So you want to load a file with some JSON arrays and search those arrays for something? I would recommend using a good JSON parser like Jackson.