Testing two JSON objects for equality ignoring child order in Java

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.

As a general architectural point, I usually advise against letting dependencies on a particular serialization format bleed out beyond your storage/networking layer; thus, I'd first recommend that you consider testing equality between your own application objects rather than their JSON manifestations.

Having said that, I'm currently a big fan of Jackson which my quick read of their ObjectNode.equals() implementation suggests does the set membership comparison that you want:

public boolean equals(Object o)
{
    if (o == this) return true;
    if (o == null) return false;
    if (o.getClass() != getClass()) {
        return false;
    }
    ObjectNode other = (ObjectNode) o;
    if (other.size() != size()) {
        return false;
    }
    if (_children != null) {
        for (Map.Entry<String, JsonNode> en : _children.entrySet()) {
            String key = en.getKey();
            JsonNode value = en.getValue();

            JsonNode otherValue = other.get(key);

            if (otherValue == null || !otherValue.equals(value)) {
                return false;
            }
        }
    }
    return true;
}

Using GSON

JsonParser parser = new JsonParser();
JsonElement o1 = parser.parse("{a : {a : 2}, b : 2}");
JsonElement o2 = parser.parse("{b : 2, a : {a : 2}}");
assertEquals(o1, o2);

Edit: Since GSON v2.8.6 the instance method JsonParser.parse is deprecated. You have to use the static method JsonParser.parseString:

JsonElement o1 = JsonParser.parseString("{a : {a : 2}, b : 2}");
JsonElement o2 = JsonParser.parseString("{b : 2, a : {a : 2}}");
assertEquals(o1, o2);