https://stackoverflow.com/questions/51767049/spring-batch-limits-number-of-concurrent-threads-to-10

MyJob.java

/*
 * Copyright 2018 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.batch.sample;

import org.springframework.batch.core.Job;
import org.springframework.batch.core.JobParameters;
import org.springframework.batch.core.JobParametersBuilder;
import org.springframework.batch.core.Step;
import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
import org.springframework.batch.core.configuration.annotation.JobBuilderFactory;
import org.springframework.batch.core.configuration.annotation.StepBuilderFactory;
import org.springframework.batch.core.configuration.annotation.StepScope;
import org.springframework.batch.core.launch.JobLauncher;
import org.springframework.batch.core.launch.support.SimpleJobLauncher;
import org.springframework.batch.core.repository.JobRepository;
import org.springframework.batch.core.step.tasklet.Tasklet;
import org.springframework.batch.repeat.RepeatStatus;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.task.TaskExecutor;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

@Configuration
@EnableBatchProcessing
public class MyJob {

	@Autowired
	private JobBuilderFactory jobs;

	@Autowired
	private StepBuilderFactory steps;

	@Autowired
	private JobRepository jobRepository;

	@Bean
	@StepScope
	public Tasklet tasklet(@Value("#{jobParameters['name']}") String name) {
		return (contribution, chunkContext) -> {
			System.out.println(Thread.currentThread().getName() + ": working on " + name);
			Thread.sleep(1000 * 10);
			System.out.println(Thread.currentThread().getName() + ": work on " + name + " done");
			return RepeatStatus.FINISHED;
		};
	}

	@Bean
	public Step step() {
		return steps.get("step")
				.tasklet(tasklet(null))
				.build();
	}

	@Bean
	public Job job() {
		return jobs.get("job")
				.start(step())
				.build();
	}

	@Bean
	public ThreadPoolTaskExecutor taskExecutor() {
		ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
		taskExecutor.setCorePoolSize(15);
		taskExecutor.setMaxPoolSize(15);
		taskExecutor.setQueueCapacity(0);
		taskExecutor.setWaitForTasksToCompleteOnShutdown(true);
		return taskExecutor;
	}

	@Bean
	public JobLauncher jobLauncher(TaskExecutor taskExecutor) {
		SimpleJobLauncher jobLauncher = new SimpleJobLauncher();
		jobLauncher.setJobRepository(jobRepository);
		jobLauncher.setTaskExecutor(taskExecutor);
		return jobLauncher;
	}

	public static void main(String[] args) throws Exception {
		ApplicationContext context = new AnnotationConfigApplicationContext(MyJob.class);
		JobLauncher jobLauncher = context.getBean(JobLauncher.class);
		Job job = context.getBean(Job.class);

		for (int i = 1; i <= 16; i++) { // submitting more jobs than the thread pool size
			JobParameters jobParameters = new JobParametersBuilder()
					.addString("name", "foo" + i)
					.toJobParameters();
			jobLauncher.run(job, jobParameters);
		}

		ThreadPoolTaskExecutor taskExecutor = context.getBean(ThreadPoolTaskExecutor.class);
		taskExecutor.shutdown();
	}

}

Output:

taskExecutor-2: working on foo2
taskExecutor-15: working on foo15
taskExecutor-14: working on foo14
taskExecutor-13: working on foo13
taskExecutor-12: working on foo12
taskExecutor-11: working on foo11
taskExecutor-10: working on foo10
taskExecutor-9: working on foo9
taskExecutor-8: working on foo8
taskExecutor-7: working on foo7
taskExecutor-6: working on foo6
taskExecutor-5: working on foo5
taskExecutor-1: working on foo1
taskExecutor-3: working on foo3
taskExecutor-4: working on foo4
taskExecutor-15: work on foo15 done
taskExecutor-14: work on foo14 done
taskExecutor-13: work on foo13 done
taskExecutor-12: work on foo12 done
taskExecutor-2: work on foo2 done
taskExecutor-11: work on foo11 done
taskExecutor-10: work on foo10 done
taskExecutor-9: work on foo9 done
taskExecutor-8: work on foo8 done
taskExecutor-7: work on foo7 done
taskExecutor-6: work on foo6 done
taskExecutor-5: work on foo5 done
taskExecutor-1: work on foo1 done
taskExecutor-3: work on foo3 done
taskExecutor-4: work on foo4 done