Spring Batch example of how to use a ClassifierCompositeItemWriter #SpringBatch https://stackoverflow.com/questions/53377660

MyJob.java

package org.springframework.batch.sample;

import java.util.Arrays;

import org.springframework.batch.core.Job;
import org.springframework.batch.core.JobParameters;
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.launch.JobLauncher;
import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.ItemWriter;
import org.springframework.batch.item.file.FlatFileItemWriter;
import org.springframework.batch.item.file.builder.FlatFileItemWriterBuilder;
import org.springframework.batch.item.file.transform.PassThroughLineAggregator;
import org.springframework.batch.item.support.ClassifierCompositeItemWriter;
import org.springframework.batch.item.support.ListItemReader;
import org.springframework.classify.Classifier;
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.io.FileSystemResource;

@Configuration
@EnableBatchProcessing
public class MyJob {

	private JobBuilderFactory jobBuilderFactory;

	private StepBuilderFactory stepBuilderFactory;

	public MyJob(JobBuilderFactory jobBuilderFactory, StepBuilderFactory stepBuilderFactory) {
		this.jobBuilderFactory = jobBuilderFactory;
		this.stepBuilderFactory = stepBuilderFactory;
	}

	@Bean
	public ItemReader<Person> itemReader() {
		Person foo1 = new Person();foo1.setId(1);foo1.setName("foo1");
		Person foo2 = new Person();foo2.setId(2);foo2.setName("foo2");
		Person bar1 = new Person();bar1.setId(3);bar1.setName("bar1");
		Person bar2 = new Person();bar2.setId(4);bar2.setName("bar2");
		return new ListItemReader<>(Arrays.asList(foo1, foo2, bar1, bar2));
	}

	@Bean
	public ClassifierCompositeItemWriter<Person> classifierCompositeItemWriter(ItemWriter<Person> fooItemWriter, ItemWriter<Person> barItemWriter) {
		ClassifierCompositeItemWriter<Person> classifierCompositeItemWriter = new ClassifierCompositeItemWriter<>();
		classifierCompositeItemWriter.setClassifier((Classifier<Person, ItemWriter<? super Person>>) person -> {
			if (person.getName().startsWith("foo")) {
				return fooItemWriter;
			} else {
				return barItemWriter;
			}
		});
		return classifierCompositeItemWriter;
	}

	@Bean
	public FlatFileItemWriter<Person> fooItemWriter() {
		return new FlatFileItemWriterBuilder<Person>()
				.name("fooItemWriter")
				.resource(new FileSystemResource("foos.txt"))
				.lineAggregator(new PassThroughLineAggregator<>())
				.build();
	}

	@Bean
	public FlatFileItemWriter<Person> barItemWriter() {
		return new FlatFileItemWriterBuilder<Person>()
				.name("barItemWriter")
				.resource(new FileSystemResource("bars.txt"))
				.lineAggregator(new PassThroughLineAggregator<>())
				.build();
	}

	@Bean
	public Step dataExtractionStep() {
		return stepBuilderFactory.get("dataExtractionStep")
				.<Person, Person>chunk(2)
				.reader(itemReader())
				.writer(classifierCompositeItemWriter(fooItemWriter(), barItemWriter()))
				.stream(fooItemWriter())
				.stream(barItemWriter())
				.build();
	}

	@Bean
	public Job dataExtractionJob() {
		return jobBuilderFactory.get("dataExtractionJob")
				.start(dataExtractionStep())
				.build();
	}

	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);
		jobLauncher.run(job, new JobParameters());
	}

	public static class Person {

		private int id;

		private String name;

		public Person() {
		}

		public Person(int id, String name) {
			this.id = id;
			this.name = name;
		}

		public int getId() {
			return id;
		}

		public void setId(int id) {
			this.id = id;
		}

		public String getName() {
			return name;
		}

		public void setName(String name) {
			this.name = name;
		}

		@Override
		public String toString() {
			return "Person{" +
					"id=" + id +
					", name='" + name + '\'' +
					'}';
		}
	}

}

XmlJobConfig.java

package io.github.benas.sbi;

import java.util.Arrays;

import javax.xml.bind.annotation.XmlRootElement;

import org.springframework.batch.core.Job;
import org.springframework.batch.core.JobParameters;
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.launch.JobLauncher;
import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.ItemWriter;
import org.springframework.batch.item.support.ClassifierCompositeItemWriter;
import org.springframework.batch.item.support.ListItemReader;
import org.springframework.batch.item.xml.StaxEventItemWriter;
import org.springframework.classify.Classifier;
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.io.FileSystemResource;
import org.springframework.oxm.jaxb.Jaxb2Marshaller;

@Configuration
@EnableBatchProcessing
public class XmlJobConfig {

	private JobBuilderFactory jobBuilderFactory;

	private StepBuilderFactory stepBuilderFactory;

	public XmlJobConfig(JobBuilderFactory jobBuilderFactory, StepBuilderFactory stepBuilderFactory) {
		this.jobBuilderFactory = jobBuilderFactory;
		this.stepBuilderFactory = stepBuilderFactory;
	}

	@Bean
	public ItemReader<Person> itemReader() {
		Person foo1 = new Person();foo1.setId(1);foo1.setName("foo1");
		Person foo2 = new Person();foo2.setId(2);foo2.setName("foo2");
		Person bar1 = new Person();bar1.setId(3);bar1.setName("bar1");
		Person bar2 = new Person();bar2.setId(4);bar2.setName("bar2");
		return new ListItemReader<>(Arrays.asList(foo1, foo2, bar1, bar2));
	}

	@Bean
	public ClassifierCompositeItemWriter<Person> classifierCompositeItemWriter(
			ItemWriter<Person> fooItemWriter,
			ItemWriter<Person> barItemWriter
	) {
		ClassifierCompositeItemWriter<Person> classifierCompositeItemWriter = new ClassifierCompositeItemWriter<>();
		classifierCompositeItemWriter.setClassifier(new Classifier<Person, ItemWriter<? super Person>>() {
			@Override
			public ItemWriter<? super Person> classify(Person person) {
				if (person.getName().startsWith("foo")) {
					return fooItemWriter;
				} else {
					return barItemWriter;
				}
			}
		});
		return classifierCompositeItemWriter;
	}

	@Bean
	public StaxEventItemWriter<Person> fooItemWriter() {
		StaxEventItemWriter<Person> itemWriter = new StaxEventItemWriter<>();
		itemWriter.setRootTagName("persons");
		itemWriter.setResource(new FileSystemResource("foos.xml"));

		Jaxb2Marshaller marshaller = new Jaxb2Marshaller();
		marshaller.setClassesToBeBound(Person.class);
		itemWriter.setMarshaller(marshaller);

		return itemWriter;
	}

	@Bean
	public StaxEventItemWriter<Person> barItemWriter() {
		StaxEventItemWriter<Person> itemWriter = new StaxEventItemWriter<>();
		itemWriter.setRootTagName("persons");
		itemWriter.setResource(new FileSystemResource("bars.xml"));

		Jaxb2Marshaller marshaller = new Jaxb2Marshaller();
		marshaller.setClassesToBeBound(Person.class);
		itemWriter.setMarshaller(marshaller);

		return itemWriter;
	}

	@Bean
	public Step dataExtractionStep() {
		return stepBuilderFactory.get("dataExtractionStep")
				.<Person, Person>chunk(2)
				.reader(itemReader())
				.writer(classifierCompositeItemWriter(fooItemWriter(), barItemWriter()))
				.stream(fooItemWriter())
				.stream(barItemWriter())
				.build();
	}

	@Bean
	public Job dataExtractionJob() {
		return jobBuilderFactory.get("dataExtractionJob")
				.start(dataExtractionStep())
				.build();
	}

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

	@XmlRootElement
	public static class Person {

		private int id;

		private String name;

		public Person() {
		}

		public Person(int id, String name) {
			this.id = id;
			this.name = name;
		}

		public int getId() {
			return id;
		}

		public void setId(int id) {
			this.id = id;
		}

		public String getName() {
			return name;
		}

		public void setName(String name) {
			this.name = name;
		}
	}

}

Is it possible to have each itemwriter write to the same file

	public FlatFileItemWriter<Person> fooItemWriter() {
		return new FlatFileItemWriterBuilder<Person>()
				.name("fooItemWriter")
				.resource(new FileSystemResource("foos.txt"))
				.lineAggregator(new PassThroughLineAggregator<>())
				.build();
	}

	@Bean
	public FlatFileItemWriter<Person> barItemWriter() {
		return new FlatFileItemWriterBuilder<Person>()
				.name("barItemWriter")
				.resource(new FileSystemResource("foos.txt"))
				.lineAggregator(new PassThroughLineAggregator<>())
				.build();
	}
``

@tommy3531

Is it possible to have each itemwriter write to the same file

That's not the goal in the first place when using a classifier composite item writer. The goal is to classify items and write them in different files. But nothing prevents you from doing it. However I'm not sure if it would work, try and see.