Revisit the configuration code of EnableBatchProcessing

Before this commit, the configuration of infrastructure beans
was confusing and not straightforward to customize. This commit
changes the way Batch infrastructure beans are configured.
The most important changes are:

* EnableBatchProcessing now provides new attributes to
configure properties of infrastructure beans
* Bean registration is now done programmatically with a
BeanDefinitionRegistrar instead of importing a class with
statically annotated bean definition methods
* Bean are now resolved from the application context directly
instead of being resolved from a BatchConfigurer
* Both a data source and a transaction manager are now
required to be defined in the application context

Issue spring-projects#3942

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/annotation/AutomaticJobRegistrarBeanPostProcessor.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2022 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
+ *
+ *      https://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.batch.core.configuration.annotation;
+
+import java.util.Iterator;
+
+import org.springframework.batch.core.configuration.JobRegistry;
+import org.springframework.batch.core.configuration.support.ApplicationContextFactory;
+import org.springframework.batch.core.configuration.support.AutomaticJobRegistrar;
+import org.springframework.batch.core.configuration.support.DefaultJobLoader;
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+
+/**
+ * Post processor that configures the {@link AutomaticJobRegistrar} registered by
+ * {@link BatchRegistrar} with required properties.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 5.0
+ */
+public class AutomaticJobRegistrarBeanPostProcessor implements BeanFactoryPostProcessor, BeanPostProcessor {
+
+	private ConfigurableListableBeanFactory beanFactory;
+
+	@Override
+	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
+		this.beanFactory = beanFactory;
+	}
+
+	@Override
+	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
+		if (bean instanceof AutomaticJobRegistrar) {
+			AutomaticJobRegistrar automaticJobRegistrar = (AutomaticJobRegistrar) bean;
+			automaticJobRegistrar.setJobLoader(new DefaultJobLoader(this.beanFactory.getBean(JobRegistry.class)));
+			for (ApplicationContextFactory factory : this.beanFactory.getBeansOfType(ApplicationContextFactory.class)
+					.values()) {
+				automaticJobRegistrar.addApplicationContextFactory(factory);
+			}
+			return automaticJobRegistrar;
+		}
+		return bean;
+	}
+
+}