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Getting Started with KaiZen OpenAPI Parser


KaiZen-OpenAPI-Parser requires a Java 8 JDK, and will require changes to build on later Java versions. All the software currently resides in a single Eclipse/Maven project located in kaizen-openapi-parser.

From this directory, you can use:

  • mvn package to build locally
  • mvn install to build and install into your local maven repository cache
  • mvn test to compile and run tests
  • etc.

Special Considerations for Tests

If you expect to frequently run tests, you should set GITHUB_AUTH environment variable to your GitHub username:password. The ExamplesTest test uses the GitHub API to retrieve the latest examples from the OAI/OpenAPI-Specification repo (specifically, folder examples/v3.0 in the master branch), and rate limits are severe for unauthenticated requests.

Regenerating Code

The KaiZen parser uses JsonOverlay to generate interfaces and implementation classes for all OpenAPI object types, based on information provided in a YAML-based DSL (types3.yaml). The git repo always contains up-to-date copies of all these generated sources, but if you ever want to regenerate them, you need to activate the gen maven profile, as in:

mvn test -P gen

Code generation takes place during the maven generate-sources phase, preceding compilation. The gen profile is disabled by default, so unless you specifically activate it, your build will use existing sources, without regeneration.

The generator makes use of a Java parser to parse existing source files before regenerating them. This is so that class members that are not marked with the @Generated annotation can be preserved during regeneration. If this parse fails for whatever reason, the overall build will be interrupted at that point and will fail. To recover from this scenario, you can check out the most recently checked-in files from your git working tree and then retry. To ensure that this will be possible as you make your own changes to the code it is recommended that you ALWAYS check in parseable copies of the generated sources after regeneration, before you begin any customization of those sources (adding non-generated members or replacements for nonrmally-generated members).

Learn About the APIs

See the API Overview for a detailed description of the APIs offered by the parser, the serializer, and the model representation, including reference treatments.

A Simple Example

You can take the parser for a spin with the following simple program, or of course explore with your own models.

The program parses each of the example OpenAPI 3.0 models currently available in the OAI/OpenAPI-Specification GitHub Repo. In each case, if validation succeeds, a summary of all the model's paths, operations and operation parameters is printed. Otherwise, all validation messages are printed.

At the time of this writing, validation fails on the callback-example because that example does not include the required openapi and info properties.

package test;

import java.util.Arrays;

import com.reprezen.jsonoverlay.Overlay;
import com.reprezen.kaizen.oasparser.OpenApi3Parser;
import com.reprezen.kaizen.oasparser.model3.OpenApi3;
import com.reprezen.kaizen.oasparser.model3.Operation;
import com.reprezen.kaizen.oasparser.model3.Parameter;
import com.reprezen.kaizen.oasparser.model3.Path;
import com.reprezen.kaizen.oasparser.model3.Schema;
import com.reprezen.kaizen.oasparser.val.ValidationResults.ValidationItem;

public class GettingStarted {

	public static void main(String[] args) throws Exception {
		boolean validate = !(args.length >= 1 && args[0].equals("-n"));
		for (String modelName : Arrays.asList("api-with-examples", "callback-example", "link-example", "petstore",
				"petstore-expanded", "uspto")) {
			URI modelUri = new URI(""
					+ modelName + ".yaml");
			processModel(modelUri, validate);

	private static void processModel(URI modelUri, boolean validate) throws Exception {
		OpenApi3 model = new OpenApi3Parser().parse(modelUri, validate);
		System.out.printf("== Model %s\n", modelUri);
		if (!validate || model.isValid()) {
		} else {
			for (ValidationItem item : model.getValidationItems()) {

	private static void describeModel(OpenApi3 model) {
		System.out.printf("Title: %s\n", model.getInfo().getTitle());
		for (Path path : model.getPaths().values()) {
			System.out.printf("Path %s:\n", Overlay.of(path).getPathInParent());
			for (Operation op : path.getOperations().values()) {
				System.out.printf("  %s: [%s] %s\n", Overlay.of(op).getPathInParent().toUpperCase(),
						op.getOperationId(), op.getSummary());
				for (Parameter param : op.getParameters()) {
					System.out.printf("    %s[%s]:, %s - %s\n", param.getName(), param.getIn(), getParameterType(param),

	private static String getParameterType(Parameter param) {
		Schema schema = param.getSchema();
		return schema != null ? schema.getType() : "unknown";

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