Validator ignores custom format about json-schema HOT 4 CLOSED

import java.util.Optional;
import org.everit.json.schema.FormatValidator;
public class EvenCharNumValidator implements FormatValidator {
    @Override
      public Optional<String> validate(final String subject) {
        if (subject.length() % 2 == 0) {
            System.out.println(subject);
          return Optional.empty();
        } else {
            System.out.println(subject);
          return Optional.of(String.format("the length of srtring [%s] is odd", subject));
        }
      }
}

        File schemaFile = new File("/Users/UserName/Downloads/schema.json");
        BufferedReader schemaBR = new BufferedReader(new FileReader(schemaFile));
        StringBuffer schemaStrbuf = new StringBuffer();
        String schemaCurrentLine;
        while ((schemaCurrentLine = schemaBR.readLine()) != null)
        {
            schemaStrbuf.append(schemaCurrentLine);
        }

        File dataFile = new File("/Users/UserName/Downloads/data.json");
        BufferedReader dataBR = new BufferedReader(new FileReader(dataFile));
        StringBuffer dataStrbuf = new StringBuffer();
        String dataCurrentLine;
        while ((dataCurrentLine = dataBR.readLine()) != null)
        {
            dataStrbuf.append(dataCurrentLine);
        }

        JSONObject jsonSchema = new JSONObject(new JSONTokener(schemaStrbuf.toString()));

        SchemaLoader schemaLoader = SchemaLoader.builder()
                .schemaJson(jsonSchema) // rawSchema is the JSON representation of the schema utilizing the "evenlength" non-standard format
                .addFormatValidator("evenlength", new EvenCharNumValidator()) // the EvenCharNumValidator gets bound to the "evenlength" keyword
                .build();

        Schema schema = schemaLoader.load().build(); // the schema is created using the above created configuration
        System.out.println(schema);


        JSONObject jsonSubject = new JSONObject(new JSONTokener(dataStrbuf.toString()));

        try
        {
            schema.validate(jsonSubject);  // the document validation happens here
        }
        catch(ValidationException ve)
        {
            System.out.println(ve.getLocalizedMessage());
        }