Please provide a way to register custom functions.

[tbarabanov]

I'm interested in adding my own custom function which I could use in JsonPath expressions. Particularly I'm interested in alphanumeric sort() function. So $.phonebook.phones.sort() should give phone numbers sorted alphanumerically. Could You please give me an advice?

[tbarabanov]

I thought I found a way but PathFunctionFactory.FUNCTIONS is unmodifiableMap. Is it possible to provide a way to register your own functions? Thanks.

[kallestenflo]

This is currently an internal API. I plan to make it public in future release. Don't know when that is...

[tbarabanov]

Ok, thanks for Your reply. Probably I can do it on my own as a workaround. Anyway It would be nice to have it in the next release.

[adrian-herscu]

Yet another usecase, this one with no reasonable workaround.

Consider a JSON like:
{ "price": "35.56" }
Now, consider this assertion:
assertThat(JSON, hasJsonPath("$.price", equalTo(34.56)));

The above assertion will throw a cast exception because "35.56" is a String.

Of course, we can rewrite the assertions to expect a String, like this:
assertThat(JSON, hasJsonPath("$.price", equalTo("34.56")));

But this will work until somebody will try to do:
assertThat(JSON, hasJsonPath("$.somevalue", allOf(greatThan("-1"), lessThan("1")));

[helsing]

@adrian-herscu In this particular case, since the json representation is a string and not a number, I think it would make sense to do the actual parsing in the assertion rather than as a customized function of the json-path. For example consider the difference when verifying a numerical json representation:

String json = "{ \"price\": 34.56 }";
assertThat(json, hasJsonPath("$.price", equalTo(34.56)));

This json would be different, and you would like your tests to detect if the json representation for some reason accidentally change to a string, right? So in your case, you could do something similar to this:

String json = "{ \"price\": \"34.56\" }";
assertThat(json, hasJsonPath("$.price", doubleAsString(equalTo(34.56))));
assertThat(json, hasJsonPath("$.price", doubleAsString(
    allOf(greaterThan(30.5), lessThan(50.0)))));

with a custom hamcrest-matcher like this:

private static Matcher<String> doubleAsString(final Matcher<? extends Number> numberMatcher) {
    return new TypeSafeMatcher<String>() {
        @Override
        protected boolean matchesSafely(String string) {
            try {
                return numberMatcher.matches(Double.valueOf(string));
            } catch (NumberFormatException e) {
                return false;
            }
        }

        @Override
        public void describeTo(Description description) {
            description.appendText("double as string ").appendDescriptionOf(numberMatcher);
        }
    };
}

This solution would gracefully catch any non-numeric content of the 'price' attribute, as well.

[adrian-herscu]

Great! Works for me :)

[jochenberger]

There's #286 and #354. They use similar approaches but differ in the details. I suggest we decide which one fits better into the current implementation and try to get it ready to be merged.

[venkatramanm]

I need this feature. +1