Add ability to start a job flow with a decider

Resolves #4411

spring-batch-core/src/main/java/org/springframework/batch/core/job/builder/FlowJobBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2011 the original author or authors.
+ * Copyright 2006-2023 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.
@@ -19,6 +19,7 @@ import org.springframework.batch.core.Job;
 import org.springframework.batch.core.Step;
 import org.springframework.batch.core.job.flow.Flow;
 import org.springframework.batch.core.job.flow.FlowJob;
+import org.springframework.batch.core.job.flow.JobExecutionDecider;
 import org.springframework.batch.core.step.builder.StepBuilderException;
 
 /**
@@ -61,6 +62,16 @@ public class FlowJobBuilder extends JobBuilderHelper<FlowJobBuilder> {
 		return new JobFlowBuilder(this, step);
 	}
 
+	/**
+	 * Start a job with this decider, but expect to transition from there to other flows
+	 * or steps.
+	 * @param decider the decider to start with
+	 * @return a builder to enable fluent chaining
+	 */
+	public JobFlowBuilder start(JobExecutionDecider decider) {
+		return new JobFlowBuilder(this, decider);
+	}
+
 	/**
 	 * Provide a single flow to execute as the job.
 	 * @param flow the flow to execute

spring-batch-core/src/main/java/org/springframework/batch/core/job/builder/JobBuilder.java

@@ -17,6 +17,7 @@ package org.springframework.batch.core.job.builder;
 
 import org.springframework.batch.core.Step;
 import org.springframework.batch.core.job.flow.Flow;
+import org.springframework.batch.core.job.flow.JobExecutionDecider;
 import org.springframework.batch.core.repository.JobRepository;
 
 /**
@@ -61,16 +62,25 @@ public class JobBuilder extends JobBuilderHelper<JobBuilder> {
 	/**
 	 * Create a new job builder that will execute a flow.
 	 * @param flow a flow to execute
-	 * @return a {@link SimpleJobBuilder}
+	 * @return a {@link JobFlowBuilder}
 	 */
 	public JobFlowBuilder start(Flow flow) {
 		return new FlowJobBuilder(this).start(flow);
 	}
 
+	/**
+	 * Create a new job builder that will start with a decider.
+	 * @param decider a decider to start with
+	 * @return a {@link JobFlowBuilder}
+	 */
+	public JobFlowBuilder start(JobExecutionDecider decider) {
+		return new FlowJobBuilder(this).start(decider);
+	}
+
 	/**
 	 * Create a new job builder that will execute a step or sequence of steps.
 	 * @param step a step to execute
-	 * @return a {@link SimpleJobBuilder}
+	 * @return a {@link JobFlowBuilder}
 	 */
 	public JobFlowBuilder flow(Step step) {
 		return new FlowJobBuilder(this).start(step);

spring-batch-core/src/test/java/org/springframework/batch/core/job/builder/FlowJobBuilderTests.java

@@ -235,6 +235,24 @@ class FlowJobBuilderTests {
 		assertEquals(2, execution.getStepExecutions().size());
 	}
 
+	@Test
+	void testBuildWithDeciderAtStart() {
+		JobExecutionDecider decider = new JobExecutionDecider() {
+			private int count = 0;
+
+			@Override
+			public FlowExecutionStatus decide(JobExecution jobExecution, @Nullable StepExecution stepExecution) {
+				count++;
+				return count < 2 ? new FlowExecutionStatus("ONGOING") : FlowExecutionStatus.COMPLETED;
+			}
+		};
+		JobFlowBuilder builder = new JobBuilder("flow", jobRepository).start(decider);
+		builder.on("COMPLETED").end().from(decider).on("*").to(step1).end();
+		builder.build().preventRestart().build().execute(execution);
+		assertEquals(BatchStatus.COMPLETED, execution.getStatus());
+		assertEquals(1, execution.getStepExecutions().size());
+	}
+
 	@Test
 	void testBuildWithIntermediateSimpleJob() {
 		SimpleJobBuilder builder = new JobBuilder("flow", jobRepository).start(step1);