Allow custom operations/providers in addition to interceptors (#654)

* Allow custom operations/providers to be added in the same way custom interceptors are currently loaded

* Add new property to documentation and default yaml file

* Add test for custom operation

src/test/java/ca/uhn/fhir/jpa/starter/CustomOperationTest.java

@@ -0,0 +1,71 @@
+package ca.uhn.fhir.jpa.starter;
+
+import ca.uhn.fhir.context.FhirContext;
+import ca.uhn.fhir.rest.api.MethodOutcome;
+import ca.uhn.fhir.rest.client.api.IGenericClient;
+import ca.uhn.fhir.rest.client.api.ServerValidationModeEnum;
+import org.hl7.fhir.r4.model.Binary;
+import org.hl7.fhir.r4.model.Parameters;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.web.server.LocalServerPort;
+
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT, classes = {Application.class}, properties = {
+		"hapi.fhir.custom-bean-packages=some.custom.pkg1",
+		"hapi.fhir.custom-provider-classes=some.custom.pkg1.CustomOperationBean,some.custom.pkg1.CustomOperationPojo",
+		"spring.datasource.url=jdbc:h2:mem:dbr4",
+		"hapi.fhir.cr_enabled=false",
+		// "hapi.fhir.enable_repository_validating_interceptor=true",
+		"hapi.fhir.fhir_version=r4"
+})
+
+class CustomOperationTest {
+
+	@LocalServerPort
+	private int port;
+
+	private IGenericClient client;
+	private FhirContext ctx;
+
+	@BeforeEach
+	void setUp() {
+		ctx = FhirContext.forR4();
+		ctx.getRestfulClientFactory().setServerValidationMode(ServerValidationModeEnum.NEVER);
+		ctx.getRestfulClientFactory().setSocketTimeout(1200 * 1000);
+		String ourServerBase = "http://localhost:" + port + "/fhir/";
+		client = ctx.newRestfulGenericClient(ourServerBase);
+
+		// Properties props = new Properties();
+		// props.put("spring.autoconfigure.exclude", "org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration");
+	}
+
+	@Test
+	void testCustomOperations() {
+
+		// we registered two custom operations via the property 'hapi.fhir.custom-provider-classes'
+		// one is discovered as a Spring Bean ($springBeanOperation), one instantiated via reflection ($pojoOperation)
+		// both should be registered with the server and will add a custom operation.
+
+		// test Spring bean operation
+		MethodOutcome springBeanOutcome = client.operation().onServer().named("$springBeanOperation")
+			.withNoParameters(Parameters.class).returnMethodOutcome().execute();
+
+		// the hapi client will return our operation result (just a string) as a Binary with the string stored as the
+		// data
+		Assertions.assertEquals(200, springBeanOutcome.getResponseStatusCode());
+		Binary springReturnResource = (Binary) springBeanOutcome.getResource();
+		String springReturn = new String(springReturnResource.getData());
+		Assertions.assertEquals("springBean", springReturn);
+
+		// test Pojo bean
+		MethodOutcome pojoOutcome = client.operation().onServer().named("$pojoOperation")
+			.withNoParameters(Parameters.class).returnMethodOutcome().execute();
+
+		Assertions.assertEquals(200, pojoOutcome.getResponseStatusCode());
+		Binary pojoReturnResource = (Binary) pojoOutcome.getResource();
+		String pojoReturn = new String(pojoReturnResource.getData());
+		Assertions.assertEquals("pojo", pojoReturn);
+	}
+}