Learn to write CSV data using FlatFileItemWriter. It is an item writer that writes data to a file or stream. The location of the output file is defined by a Resource and must represent a writable file.
Table of Contents Project Structure Write data CSV files with FlatFileItemWriter Maven Dependency Demo
Project Structure
In this project, we will learn to –
- Read 3 CSV files from
input/*.csvusingMultiResourceItemReader. - Write whole data to
output/outputData.csvfile usingFlatFileItemWriter.
Write data CSV files with FlatFileItemWriter
You need to use FlatFileItemWriter to write lines which were read from CSV files. It write the content to any Resource passed to writer.setResource() method.
package com.howtodoinjava.demo.config;
import org.springframework.batch.core.Job;
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.support.RunIdIncrementer;
import org.springframework.batch.item.file.FlatFileItemReader;
import org.springframework.batch.item.file.FlatFileItemWriter;
import org.springframework.batch.item.file.MultiResourceItemReader;
import org.springframework.batch.item.file.mapping.BeanWrapperFieldSetMapper;
import org.springframework.batch.item.file.mapping.DefaultLineMapper;
import org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor;
import org.springframework.batch.item.file.transform.DelimitedLineAggregator;
import org.springframework.batch.item.file.transform.DelimitedLineTokenizer;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.FileSystemResource;
import org.springframework.core.io.Resource;
import com.howtodoinjava.demo.model.Employee;
@Configuration
@EnableBatchProcessing
public class BatchConfig
{
@Autowired
private JobBuilderFactory jobBuilderFactory;
@Autowired
private StepBuilderFactory stepBuilderFactory;
@Value("input/inputData*.csv")
private Resource[] inputResources;
private Resource outputResource = new FileSystemResource("output/outputData.csv");
@Bean
public FlatFileItemWriter<Employee> writer()
{
//Create writer instance
FlatFileItemWriter<Employee> writer = new FlatFileItemWriter<>();
//Set output file location
writer.setResource(outputResource);
//All job repetitions should "append" to same output file
writer.setAppendAllowed(true);
//Name field values sequence based on object properties
writer.setLineAggregator(new DelimitedLineAggregator<Employee>() {
{
setDelimiter(",");
setFieldExtractor(new BeanWrapperFieldExtractor<Employee>() {
{
setNames(new String[] { "id", "firstName", "lastName" });
}
});
}
});
return writer;
}
@Bean
public Job readCSVFilesJob() {
return jobBuilderFactory
.get("readCSVFilesJob")
.incrementer(new RunIdIncrementer())
.start(step1())
.build();
}
@Bean
public Step step1() {
return stepBuilderFactory.get("step1").<Employee, Employee>chunk(5)
.reader(multiResourceItemReader())
.writer(writer())
.build();
}
@Bean
public MultiResourceItemReader<Employee> multiResourceItemReader()
{
MultiResourceItemReader<Employee> resourceItemReader = new MultiResourceItemReader<Employee>();
resourceItemReader.setResources(inputResources);
resourceItemReader.setDelegate(reader());
return resourceItemReader;
}
@SuppressWarnings({ "rawtypes", "unchecked" })
@Bean
public FlatFileItemReader<Employee> reader()
{
//Create reader instance
FlatFileItemReader<Employee> reader = new FlatFileItemReader<Employee>();
//Set number of lines to skips. Use it if file has header rows.
reader.setLinesToSkip(1);
//Configure how each line will be parsed and mapped to different values
reader.setLineMapper(new DefaultLineMapper() {
{
//3 columns in each row
setLineTokenizer(new DelimitedLineTokenizer() {
{
setNames(new String[] { "id", "firstName", "lastName" });
}
});
//Set values in Employee class
setFieldSetMapper(new BeanWrapperFieldSetMapper<Employee>() {
{
setTargetType(Employee.class);
}
});
}
});
return reader;
}
}
public class Employee {
String id;
String firstName;
String lastName;
//public setter and getter methods
}
id,firstName,lastName 1,Lokesh,Gupta 2,Amit,Mishra 3,Pankaj,Kumar 4,David,Miller
id,firstName,lastName 5,Ramesh,Gupta 6,Vineet,Mishra 7,Amit,Kumar 8,Dav,Miller
id,firstName,lastName 9,Vikas,Kumar 10,Pratek,Mishra 11,Brian,Kumar 12,David,Cena
Maven Dependency
Look at project dependencies.
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd; <modelVersion>4.0.0</modelVersion> <groupId>com.howtodoinjava</groupId> <artifactId>App</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>App</name> <url>http://maven.apache.org</url> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.3.RELEASE</version> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-batch</artifactId> </dependency> <dependency> <groupId>com.h2database</groupId> <artifactId>h2</artifactId> <scope>runtime</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> <repositories> <repository> <id>repository.spring.release</id> <name>Spring GA Repository</name> <url>http://repo.spring.io/release</url> </repository> </repositories> </project>
Demo
Before running the application, look at complete code of App.java which run the application as Spring boot application.
package com.howtodoinjava.demo;
import org.springframework.batch.core.Job;
import org.springframework.batch.core.JobParameters;
import org.springframework.batch.core.JobParametersBuilder;
import org.springframework.batch.core.launch.JobLauncher;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.annotation.Scheduled;
@SpringBootApplication
@EnableScheduling
public class App
{
@Autowired
JobLauncher jobLauncher;
@Autowired
Job job;
public static void main(String[] args)
{
SpringApplication.run(App.class, args);
}
@Scheduled(cron = "0 */1 * * * ?")
public void perform() throws Exception
{
JobParameters params = new JobParametersBuilder()
.addString("JobID", String.valueOf(System.currentTimeMillis()))
.toJobParameters();
jobLauncher.run(job, params);
}
}
#Disable batch job's auto start spring.batch.job.enabled=false spring.main.banner-mode=off
Run the application
Run the application as Spring boot application, and watch the console. Batch job will start at start of each minute. It will read the input file, and print the read values in console.
1,Lokesh,Gupta 2,Amit,Mishra 3,Pankaj,Kumar 4,David,Miller 5,Ramesh,Gupta 6,Vineet,Mishra 7,Amit,Kumar 8,Dav,Miller 9,Vikas,Kumar 10,Pratek,Mishra 11,Brian,Kumar 12,David,Cena
Drop me your questions in comments section.
Happy Learning !!