Embed the API

The REST API is an artifact of its own, which means that it can be embedded in any other JAX-RS application independently of the engine.

Prerequisites

The REST API classes are tested with Resteasy, Jersey and Wink as the JAX-RS implementation. Furthermore, the engine classes and Jackson’s com.fasterxml.jackson.jaxrs:jackson-jaxrs-json-provider artifact (as well as transitive Jackson dependencies) have to be on the classpath.

Required Steps

Step 1: Add the REST API to your project as a Maven dependency.

Please import the Camunda BOM to ensure correct versions for every Camunda project.

<dependency>
  <groupId>org.camunda.bpm</groupId>
  <artifactId>camunda-engine-rest</artifactId>
  <classifier>classes</classifier>
</dependency>

Step 2: Add the REST resources that you need to your JAX-RS application. Example:

@ApplicationPath("/")
public class MyApplication extends Application {
  @Override
  public Set<Class<?>> getClasses() {
    Set<Class<?>> classes = new HashSet<Class<?>>();
    // add your own classes
    ...
    // add all camunda engine rest resources (or just add those that you actually need).
    classes.addAll(CamundaRestResources.getResourceClasses());

    // mandatory
    classes.addAll(CamundaRestResources.getConfigurationClasses());

    return classes;
  }
}

CamundaRestResources.getResourceClasses() contains two JAX-RS resources that serve as the entry points. One of these (org.camunda.bpm.engine.rest.impl.NamedProcessEngineRestServiceImpl) provides all of the REST resources listed in this document on paths beginning with /engine/{name} while the other (org.camunda.bpm.engine.rest.impl.DefaultProcessEngineRestServiceImpl) provides access to the default engine’s resources on the root path /.

To restrict the exposed REST resources to specific types (e.g. only process-definition-related methods), a subclass of org.camunda.bpm.engine.rest.impl.AbstractProcessEngineRestServiceImpl can be implemented and registered with the JAX-RS application. Such a subclass can control which resources get exposed by offering JAX-RS-annotated methods. See the sources of NamedProcessEngineRestServiceImpl and DefaultProcessEngineRestServiceImpl for an example. Note: The path to a subresource should always match the path defined in the subresource’s interface.

The configuration class JacksonConfigurator is required to correctly configure the serialization of date fields. You may also have to add the following Jackson providers: com.fasterxml.jackson.jaxrs.json.JacksonJsonProvider, org.camunda.bpm.engine.rest.exception.JsonMappingExceptionHandler and org.camunda.bpm.engine.rest.exception.JsonParseExceptionHandler. Depending on the runtime environment, this may not be necessary. On JBoss AS 7/Wildfly 8 these should be automatically added as an implicit module dependency.

For proper exception responses of the format as described in the Introduction, it is necessary to include RestExceptionHandler. ProcessEngineExceptionHandler is used to translate any exception thrown by the engine that is not explicitly handled by the REST API classes to a generic HTTP 500 error with the same response body format. If you would like to have all kinds of exceptions translated to this format, you can use org.camunda.bpm.engine.rest.exception.ExceptionHandler instead of ProcessEngineExceptionHandler.

Next is the wiring of the REST API and the process engine(s). To do this, you must create a Service Provider that implements the interface ProcessEngineProvider and declare it in a file META-INF/services/org.camunda.bpm.engine.rest.spi.ProcessEngineProvider. You may also declare the class org.camunda.bpm.engine.rest.impl.application.ContainerManagedProcessEngineProvider which comes with the REST API and uses the methods that the class org.camunda.bpm.BpmPlatform provides.

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