Matching json with mockito

example.md

Now you can use json string as argument matchers

when(myMock.methodCall(jsonEq("{\"firstName\":\"Bill\", \"lastName\":\"Gates\"}"))).thenReturn(myResponse);

or

verify(myMock, times(1)).methodCall(jsonEq("{\"firstName\":\"Bill\", \"lastName\":\"Gates\"}")));

which is useful as it'll be safer than testing with raw string values. This approach allows the json structure to have the fields in any order and will also match regardless of multiple lines or minimal whitespace.

TestUtils.java

import org.mockito.ArgumentMatcher;

// javax.json:javax.json-api
//import javax.json.Json;
//import javax.json.JsonStructure;
//import javax.json.stream.JsonGenerator;

// jakarta.json:jakarta.json-api
import jakarta.json.Json;
import jakarta.json.JsonStructure;
import jakarta.json.stream.JsonGenerator;

import java.io.IOException;
import java.io.Serializable;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.Collections;
import java.util.Map;

import static org.mockito.ArgumentMatchers.argThat;

/**
* Reusable code for test classes
*
*/
public class TestUtils {

    public static String jsonEq(String val) {
        // if this was inside mockito it'd be reportMatcher(new JsonEquals(val));
        argThat(new JsonEquals(val));
        return val;
    }

    static class JsonEquals implements ArgumentMatcher<String> {
        private static final Map<String, Object> OPTIONS = Collections.singletonMap(JsonGenerator.PRETTY_PRINTING, true);
        private final String value;
        private final JsonStructure json;

        public JsonEquals(final String value) {
            if (value == null) throw new IllegalArgumentException("string value is null");
            this.value = value;
            this.json = Json.createReader(new StringReader(value)).read();
        }

        @Override
        public boolean matches(String arg) {
            final JsonStructure argJson = Json.createReader(new StringReader(arg)).read();

            return json.equals(argJson);
        }

        @Override
        public String toString() {
            try (final StringWriter writer = new StringWriter()) {
                Json.createWriterFactory(OPTIONS)
                        .createWriter(writer)
                        .write(json);
                return writer.toString();
            } catch (final IOException e) {
                e.printStackTrace();
                return value;
            }
        }
    }

}