java - Ignore specific nodes/attributes while comparing two JSONs

Question

I want to compare two JSON strings which is a huge hierarchy and want to know where they differ in values. But some values are generated at runtime and are dynamic. I want to ignore those particular nodes from my comparison.

I am currently using JSONAssert from org.SkyScreamer to do the comparison. It gives me nice console output but does not ignore any attributes.

for ex.

java.lang.AssertionError messageHeader.sentTime
expected:null
got:09082016 18:49:41.123

Now this comes dynamic and should be ignored. Something like

JSONAssert.assertEquals(expectedJSONString, actualJSONString,JSONCompareMode, *list of attributes to be ignored*)

It would be great if someone suggests a solution in JSONAssert. However other ways are also welcome.

Answer 1

You can use Customization for this. For example, if you need to ignore a top-level attribute named "timestamp" use:

JSONAssert.assertEquals(expectedResponseBody, responseBody,
            new CustomComparator(JSONCompareMode.LENIENT,
                new Customization("timestamp", (o1, o2) -> true)));

It's also possible to use path expressions like "entry.id". In your Customization you can use whatever method you like to compare the two values. The example above always returns true, no matter what the expected value and the actual value are. You could do more complicated stuff there if you need to.

It is perfectly fine to ignore that values of multiple attributes, for example:

@Test
public void ignoringMultipleAttributesWorks() throws JSONException {
    String expected = "{"timestamp":1234567, "a":5, "b":3 }";
    String actual = "{"timestamp":987654, "a":1, "b":3 }";

    JSONAssert.assertEquals(expected, actual,
            new CustomComparator(JSONCompareMode.LENIENT,
                    new Customization("timestamp", (o1, o2) -> true),
                    new Customization("a", (o1, o2) -> true)
            ));
}

There is one caveat when using Customizations: The attribute whose value is to be compared in a custom way has to be present in the actual JSON. If you want the comparison to succeed even if the attribute is not present at all you would have to override CustomComparator for example like this:

@Test
public void extendingCustomComparatorToAllowToCompletelyIgnoreCertainAttributes() throws JSONException {
    // AttributeIgnoringComparator completely ignores some of the expected attributes
    class AttributeIgnoringComparator extends CustomComparator{
        private final Set<String> attributesToIgnore;

        private AttributeIgnoringComparator(JSONCompareMode mode, Set<String> attributesToIgnore, Customization... customizations) {
            super(mode, customizations);
            this.attributesToIgnore = attributesToIgnore;
        }

        protected void checkJsonObjectKeysExpectedInActual(String prefix, JSONObject expected, JSONObject actual, JSONCompareResult result) throws JSONException {
            Set<String> expectedKeys = getKeys(expected);
            expectedKeys.removeAll(attributesToIgnore);
            for (String key : expectedKeys) {
                Object expectedValue = expected.get(key);
                if (actual.has(key)) {
                    Object actualValue = actual.get(key);
                    compareValues(qualify(prefix, key), expectedValue, actualValue, result);
                } else {
                    result.missing(prefix, key);
                }
            }
        }
    }

    String expected = "{"timestamp":1234567, "a":5}";
    String actual = "{"a":5}";

    JSONAssert.assertEquals(expected, actual,
            new AttributeIgnoringComparator(JSONCompareMode.LENIENT,
                    new HashSet<>(Arrays.asList("timestamp")))
            );
} 

(With this approach you still could use Customizations to compare other attributes' values in the way you want.)