Add Task Event Listener

Adds a Task Listener that emits the TaskExecution as an event via a
Spring Cloud Stream channel (essentially the listener serves as a SCSt
Source).

Resolves spring-cloud/spring-cloud-task#11

spring-cloud-task-stream/src/main/java/org/springframework/cloud/task/listener/TaskEventAutoConfiguration.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.cloud.task.listener;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.cloud.stream.annotation.EnableBinding;
+import org.springframework.cloud.stream.annotation.Output;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.PropertySource;
+import org.springframework.integration.gateway.GatewayProxyFactoryBean;
+import org.springframework.messaging.MessageChannel;
+
+/**
+ *
+ * @author Michael Minella
+ */
+@Configuration
+@ConditionalOnClass(EnableBinding.class)
+@ConditionalOnBean(TaskLifecycleListener.class)
+@ConditionalOnProperty(prefix = "spring.cloud.task.events", name = "enabled", havingValue = "true", matchIfMissing = true)
+@PropertySource("classpath:/org/springframework/cloud/task/application.properties")
+public class TaskEventAutoConfiguration {
+
+	@Configuration
+	@EnableBinding(TaskEventChannels.class)
+	public static class ListenerConfiguration {
+
+		@Autowired
+		private TaskEventChannels taskEventChannels;
+
+		@Bean
+		public GatewayProxyFactoryBean taskEventListener() {
+			GatewayProxyFactoryBean factoryBean =
+					new GatewayProxyFactoryBean(TaskExecutionListener.class);
+
+			factoryBean.setDefaultRequestChannel(taskEventChannels.taskEvents());
+
+			return factoryBean;
+		}
+	}
+
+	public interface TaskEventChannels {
+
+		String TASK_EVENTS = "task-events";
+
+		@Output(TASK_EVENTS)
+		MessageChannel taskEvents();
+	}
+}

spring-cloud-task-stream/src/main/resources/META-INF/spring.factories

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+org.springframework.boot.autoconfigure.EnableAutoConfiguration=org.springframework.cloud.task.listener.TaskEventAutoConfiguration

spring-cloud-task-stream/src/main/resources/org/springframework/cloud/task/application.properties

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+spring.cloud.stream.bindings.task-events.contentType=application/json