Spring Bactch writes empty file - spring

Question

I am new to batch programming and I am using Spring Batch. tried to use some online examples but after fixing lot of errors i am getting an empty file. I am trying to read from a simple MySql database and writing to a CSV file. users.csv is located in resource folder. Spent a lot of time to see what wrong I am doing. There is no error message but it is always showing empty file. I would really appreciate if anyone can help me to fix this issue. Here is my code;
BatchConfig.class
#Configuration
#EnableBatchProcessing
public class BatchConfig {
#Autowired
private JobBuilderFactory jobBuilderFactory;
#Autowired
private StepBuilderFactory stepBuilderFactory;
#Autowired
private DataSource dataSource;
#Bean
public JdbcCursorItemReader<User> reader(){
JdbcCursorItemReader<User> cursorItemReader = new JdbcCursorItemReader<>();
cursorItemReader.setDataSource(dataSource);
cursorItemReader.setSql("SELECT user_id,first_name,last_name,email FROM demodb.user");
cursorItemReader.setRowMapper(new UserRowMapper());
return cursorItemReader;
}
#Bean
public UserItemProcessor processor(){
return new UserItemProcessor();
}
#Bean
public FlatFileItemWriter<User> writer(){
FlatFileItemWriter<User> writer = new FlatFileItemWriter<User>();
writer.setResource(new ClassPathResource("users.csv"));
DelimitedLineAggregator<User> lineAggregator = new DelimitedLineAggregator<User>();
lineAggregator.setDelimiter(",");
BeanWrapperFieldExtractor<User> fieldExtractor = new BeanWrapperFieldExtractor<User>();
fieldExtractor.setNames(new String[]{"userId","firstName","lastName", "email"});
lineAggregator.setFieldExtractor(fieldExtractor);
writer.setLineAggregator(lineAggregator);
return writer;
}
#Bean
public Step step1(){
return stepBuilderFactory
.get("step1")
.<User,User>chunk(100)
.reader(reader())
.processor(processor())
.writer(writer())
.build();
}
#Bean
public Job exportUserJob(){
return jobBuilderFactory
.get("exportUserJob")
.incrementer(new RunIdIncrementer())
.flow(step1())
.end()
.build();
}
}
UserRowMapper.class
public class UserRowMapper implements RowMapper<User> {
#Override
public User mapRow(ResultSet rs, int rowNum) throws SQLException {
User user = new User();
user.setUserId(rs.getInt("user_id"));
user.setFirstName(rs.getString("first_name"));
user.setLastName(rs.getString("last_name"));
user.setEmail(rs.getString("email"));
return user;
}
}
User.class
public class User {
private int userId;
private String firstName;
private String lastName;
private String email;
public int getUserId() {
return userId;
}
public void setUserId(int userId) {
this.userId = userId;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}
UserItemProcessor.class
public class UserItemProcessor implements ItemProcessor<User, User>{
#Override
public User process(User person) throws Exception {
return person;
}
}
application.properties
spring.datasource.url=jdbc:mysql://localhost:3306/demodb
spring.datasource.password=root
spring.datasource.username=root
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.batch.initialize-schema=ALWAYS
MySql db
UPDATE
I could solve the issue with new file new FileSystemResource(). But I was replicating a business use case issue. As I mentioned I am new to Spring batch and I have a requirement to read from a production database where I have only View permission. I come to know that Spring batch uses metadata tables to process the Batch. So is it required to have a write permission to the table ? If that is the case then I wont be able to use spring batch with only View permission in production environment. Is there any way I can work around this ? Overriding any configuration ?

Answer 1

Try to decrease chunk value
chunk: Indicates that this is an item based step and the number of items to be processed before the transaction is committed.

Answer 2

Use FileSystemResource instead of ClassPathResource in your writer's configuration:
writer.setResource(new FileSystemResource("users.csv"));

Answer 3

I have verified this by running this program, is working fine as it is and no issue
Issue:
As I mentioned in the comments below, user is looking at the file at the wrong location.
User creates a file at src/main/resources/users.csv
User runs the program
Files gets copied under target/classes/users.csv
Program is writing to the file under target/classes/users.csv
But user was looking the file at src/main/resources/users.csv