Back port of Task Thin Execution List and List By Name

Updates api docs for tasks/thinexecutions/name and all HATEOAS links. Updates related tests for links.
Update find by name to return 404 when task definition doesn't exist.
Update version checking in TaskTemplate.

Fixes #5995

Author: Corneil du Plessis

spring-cloud-dataflow-rest-client/src/main/java/org/springframework/cloud/dataflow/rest/client/TaskTemplate.java

@@ -71,6 +71,7 @@ public class TaskTemplate implements TaskOperations {
 	private static final String VALIDATION_THIN_TASK_VERSION = "2.11.3";
 
 	private static final String VALIDATION_TASK_LAUNCH_VERSION = "2.11.0";
+	private static final String VALIDATION_TASK_THIN_BY_NAME = "2.11.6";
 
 	private static final String EXECUTIONS_RELATION = "tasks/executions";
 
@@ -145,14 +146,43 @@ public class TaskTemplate implements TaskOperations {
 
 		this.restTemplate = restTemplate;
 		this.dataFlowServerVersion = dataFlowServerVersion;
+		String version = VersionUtils.getThreePartVersion(dataFlowServerVersion);
+		if (VersionUtils.isDataFlowServerVersionGreaterThanOrEqualToRequiredVersion(version, EXECUTIONS_CURRENT_RELATION_VERSION)) {
+			Assert.isTrue(resources.getLink(EXECUTIONS_CURRENT_RELATION).isPresent(), ()-> EXECUTIONS_CURRENT_RELATION + " relation is required");
+			this.executionsCurrentLink = resources.getLink(EXECUTIONS_CURRENT_RELATION).get();
+		} else {
+			this.executionsCurrentLink = null;
+		}
+		if (VersionUtils.isDataFlowServerVersionGreaterThanOrEqualToRequiredVersion(version, VALIDATION_RELATION_VERSION)) {
+			Assert.isTrue(resources.getLink(VALIDATION_REL).isPresent(), ()->VALIDATION_REL + " relation is required");
+			this.validationLink = resources.getLink(VALIDATION_REL).get();
+		} else {
+			this.validationLink = null;
+		}
 
-		this.validationLink = resources.getLink(VALIDATION_REL).get();
-		this.aboutLink = resources.getLink("about").get();
 
-		this.thinExecutionsLink = resources.getLink(THIN_EXECUTIONS_RELATION).orElse(null);
-		this.thinExecutionsByNameLink = resources.getLink(THIN_EXECUTIONS_BY_NAME_RELATION).orElse(null);
-		this.executionLaunchLink = resources.getLink(EXECUTION_LAUNCH_RELATION).orElse(null);
-		this.executionsCurrentLink = resources.getLink(EXECUTIONS_CURRENT_RELATION).orElse(null);
+		if(VersionUtils.isDataFlowServerVersionGreaterThanOrEqualToRequiredVersion(version, VALIDATION_THIN_TASK_VERSION) && resources.getLink(THIN_EXECUTIONS_RELATION).isPresent()) {
+			Assert.isTrue(resources.getLink(THIN_EXECUTIONS_RELATION).isPresent(), () -> THIN_EXECUTIONS_RELATION + " relation is required");
+			this.thinExecutionsLink = resources.getLink(THIN_EXECUTIONS_RELATION).get();
+		} else {
+			this.thinExecutionsLink = null;
+		}
+		if(VersionUtils.isDataFlowServerVersionGreaterThanOrEqualToRequiredVersion(version, VALIDATION_TASK_THIN_BY_NAME)) {
+			Assert.isTrue(resources.getLink(THIN_EXECUTIONS_BY_NAME_RELATION).isPresent(), () -> THIN_EXECUTIONS_BY_NAME_RELATION + " relation is required");
+			this.thinExecutionsByNameLink = resources.getLink(THIN_EXECUTIONS_BY_NAME_RELATION).get();
+		} else {
+			this.thinExecutionsByNameLink = null;
+		}
+
+		if (VersionUtils.isDataFlowServerVersionGreaterThanOrEqualToRequiredVersion(version, VALIDATION_TASK_LAUNCH_VERSION)) {
+			Assert.isTrue(resources.getLink(EXECUTION_LAUNCH_RELATION).isPresent(), () -> EXECUTION_LAUNCH_RELATION + " relation is required");
+			this.executionLaunchLink = resources.getLink(EXECUTION_LAUNCH_RELATION).get();
+		} else {
+			this.executionLaunchLink = null;
+		}
+
+
+		this.aboutLink = resources.getLink("about").get();
 
 		this.definitionsLink = resources.getLink(DEFINITIONS_RELATION).get();
 		this.definitionLink = resources.getLink(DEFINITION_RELATION).get();

spring-cloud-dataflow-rest-client/src/test/java/org/springframework/cloud/dataflow/rest/client/TaskTemplateTests.java

@@ -54,14 +54,12 @@ public void testOldDataFlow() {
 
 	@Test
 	public void testMinDataFlow() {
-		validateExecutionLinkPresent("1.7.0");
+		validateExecutionLinkPresent("2.10.0");
 	}
 
 	@Test
 	public void testFutureDataFlow() {
-		validateExecutionLinkPresent("1.8.0");
-		validateExecutionLinkPresent("1.9.0");
-		validateExecutionLinkPresent("2.0.0");
+		validateExecutionLinkPresent("2.11.6");
 	}