Jackson Json parser has a nice feature that it can parse a Json String into a Map. You can then query the entries or simply ask on equality:

import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.*;

public class Test
{
    public static void main(String... args)
    {
        String input1 = "{\"state\":1,\"cmd\":1}";
        String input2 = "{\"cmd\":1,\"state\":1}";
        ObjectMapper om = new ObjectMapper();
        try {
            Map<String, Object> m1 = (Map<String, Object>)(om.readValue(input1, Map.class));
            Map<String, Object> m2 = (Map<String, Object>)(om.readValue(input2, Map.class));
            System.out.println(m1);
            System.out.println(m2);
            System.out.println(m1.equals(m2));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The output is

{state=1, cmd=1}
{cmd=1, state=1}
true

I recommend the zjsonpatch library, which presents the diff information in accordance with RFC 6902 (JSON Patch). You can use it with Jackson:

import com.fasterxml.jackson.databind.{ObjectMapper, JsonNode}
JsonNode beforeNode = jacksonObjectMapper.readTree(beforeJsonString);
JsonNode afterNode = jacksonObjectMapper.readTree(afterJsonString);

import com.flipkart.zjsonpatch.JsonDiff
JsonNode patch = JsonDiff.asJson(beforeNode, afterNode);
String diffs = patch.toString();

This library is better than fge-json-patch (which was mentioned in another answer) because it can detect items being inserted/removed from arrays. Fge-json-patch cannot handle that (if an item is inserted into the middle of an array, it will think that item and every item after that was changed since they are all shifted over by one).

Try Skyscreamer's JSONAssert.

Its non-strict mode has two major advantages that make it less brittle:

• Object extensibility (e.g. With an expected value of {id:1}, this would still pass: {id:1,moredata:'x'}.)
• Loose array ordering (e.g. ['dog','cat']==['cat','dog'])

In strict mode it behaves more like json-lib's test class.

A test looks something like this:

@Test
public void testGetFriends() {
    JSONObject data = getRESTData("/friends/367.json");
    String expected = "{friends:[{id:123,name:\"Corby Page\"}"
        + ",{id:456,name:\"Solomon Duskis\"}]}";
    JSONAssert.assertEquals(expected, data, false);
}

The parameters in the JSONAssert.assertEquals() call are expectedJSONString, actualDataString, and isStrict.

The result messages are pretty clear, which is important when comparing really big JSON objects.