How can we take the result of `MethodInvokingTaskletAdapter` as a reader in the Spring Batch Step? - spring

Question

How can we take the result of MethodInvokingTaskletAdapter as a reader in the Spring Batch Step? Reference - https://docs.spring.io/spring-batch/docs/current/reference/html/index-single.html#taskletStep and https://github.com/spring-projects/spring-batch/pull/567
Here is the code that I developed
JobConfiguration.java
#Configuration
public class JobConfiguration {
#Autowired
private JobBuilderFactory jobBuilderFactory;
#Autowired
private StepBuilderFactory stepBuilderFactory;
#Bean
public CustomService service() {
return new CustomService();
}
#StepScope
#Bean
public MethodInvokingTaskletAdapter methodInvokingTasklet() {
MethodInvokingTaskletAdapter methodInvokingTaskletAdapter = new MethodInvokingTaskletAdapter();
methodInvokingTaskletAdapter.setTargetObject(service());
methodInvokingTaskletAdapter.setTargetMethod("getEmployees");
return methodInvokingTaskletAdapter;
}
#Bean
public Job methodInvokingJob() {
return this.jobBuilderFactory.get("methodInvokingJob")
.start(methodInvokingStep())
.build();
}
#Bean
public Step methodInvokingStep() {
// Looking to configure the Chunk based Step here, dont know how to do using MethodInvokingTaskletAdapter
return this.stepBuilderFactory.get("methodInvokingStep")
.tasklet(methodInvokingTasklet())
.build();
}
}
CustomService.java
public class CustomService {
public void serviceMethod(String message) {
System.out.println(message);
}
public void invokeMethod() {
System.out.println("=============== Your method has executed !");
}
public List<Employee> getEmployees(){
// In real world, it will be an GET API call to XYZ system
List<Employee> employees = new ArrayList<>();
employees.add(Employee.builder().firstName("Ravi").lastName("Shankar").email("ravi.shankar#gmail.com").age(30).build());
employees.add(Employee.builder().firstName("Parag").lastName("Rane").email("parag.rane#gmail.com").age(11).build());
employees.add(Employee.builder().firstName("Priya").lastName("Pande").email("priya.pande#gmail.com").age(40).build());
employees.add(Employee.builder().firstName("Kiran").lastName("khot").email("kiran.khot#gmail.com").age(50).build());
return employees;
}
}
Employee.java
#Data
#AllArgsConstructor
#NoArgsConstructor
#Builder
public class Employee {
private String firstName;
private String lastName;
private String email;
private int age;
}
MethodInvokingTaskletApplication.java
#EnableBatchProcessing
#SpringBootApplication
public class MethodInvokingTaskletApplication {
public static void main(String[] args) {
SpringApplication.run(MethodInvokingTaskletApplication.class, args);
}
}

Answer 1

To answer your question, you can't. The MethodInvokingTaskletAdapter is meant to adapt a POJO to a Tasklet. We have an ItemReaderAdapter that you can use to adapt a POJO to an ItemReader. You can read about it in the documentation here: https://docs.spring.io/spring-batch/docs/current/api/org/springframework/batch/item/adapter/ItemReaderAdapter.html
Now you'll have an issue with your service as configured in that each call to the delegating POJO is considered an item. That means that your item as configured will be a List<Employee> instead of just an Employee. Given your configuration states it's not the real service, I'll assume that your real service should return an Employee per call and null once the results are exhausted.
To update your configuration (with your service as it is configured in your question) in your sample:
...
#StepScope
#Bean
public ItemReaderAdapter itemReader() {
ItemReaderAdapter reader = new ItemReaderAdapter();
reader.setTargetObject(service());
reader.setTargetMethod("getEmployees");
return reader;
}
#Bean
public Job methodInvokingJob() {
return this.jobBuilderFactory.get("methodInvokingJob")
.start(methodInvokingStep())
.build();
}
#Bean
public Step methodInvokingStep() {
return this.stepBuilderFactory.get("methodInvokingStep")
.<List<Employee>, List<Employee>>chunk(methodInvokingTasklet())
.reader(itemReader())
// You'll need to define a writer...
.writer(itemWriter())
.build();
}
...