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Diff Field Builder

The "diff" field builder is useful for debugging a change in state in complex objects because it can compare "before" and "after" objects and only render the changes between the two values, using RFC 6902 format with zjsonpatch.

To add the diff field builder, add the diff module:

implementation "com.tersesystems.echopraxia:diff:<VERSION>"

And implement DiffFieldBuilder:

import com.tersesystems.echopraxia.diff.DiffFieldBuilder;

class PersonFieldBuilder implements DiffFieldBuilder {
  // ...
  public FieldBuilderResult diff(String name, Person before, Person after) {
    return diff(name, personValue(before), personValue(after), Field.class);

You can then compare a change in an object by rendering the diff:

Logger<PersonFieldBuilder> logger = LoggerFactory.getLogger().withFieldBuilder(PersonFieldBuilder.instance);

Person before = new Person("Jim", 1);
Person after = before.withName("Will");"{}", fb -> fb.diff("personDiff", before, after));

The diff field builder depends on Jackson 2.13, and will use a static object mapper by default, which you can override using the _objectMapper method.