Spring batch item writer rest API

Question

Is it possible to read data from DB, process it and in ItemWriter send to another system using RestAPI (REST TEMPLATE) in Spring batch project? All I can see is fetch data and write it in a csv file.

Answer 1

It is possible to create your own custom ItemWriter.

In your case, please add the spring-boot-starter-web dependency to either your pom.xml or build.gradle

Example:

package com.example.batch;

import lombok.extern.log4j.Log4j2;
import org.springframework.batch.item.ItemWriter;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;

import java.util.List;

@Log4j2
public class RestItemWriter implements ItemWriter<String> {
    @Autowired
    RestTemplate restTemplate;

    public RestItemWriter(RestTemplate restTemplate) {
        this.restTemplate = restTemplate;
    }

    @Override
    public void write(List<? extends String> items) throws Exception {
        ResponseEntity<Users> users = restTemplate.getForEntity("https://jsonplaceholder.typicode.com/users/1", Users.class);

        log.info("Status code is: " + users.getStatusCode());
    }
}


package com.example.batch;

import com.fasterxml.jackson.annotation.JsonInclude;
import lombok.Getter;
import lombok.Setter;

@Getter
@Setter
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Users {

    public String id;
    public String name;
    public String username;
    public String email;
    public String phone;
}

More information about custom item writers here

Answer 2

Of course! you can send the processed records to another system using REST call in ItemWriter.

Use the below code in your RestItemWriter class.

private RestTemplate restTemplate;

@Override
public void write(@NonNull Chunk<? extends Payload> chunk) throws Exception {

    for((Payload payload : chunk){

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.set("Authorization", "xx-tokenString-xx");
                    
        HttpEntity<Payload> requestEntity = new HttpEntity<>(payload, headers);

        try{
            ResponseEntity<Object> response = restTemplate.exchange(url, HttpMethod.PATCH, requestEntity, Object.class);
            LOGGER.info("Request hits the server {}", response.getBody());
        } catch(HttpClientErrorException e){
            LOGGER.error("HttpClientErrorException occured during connection {}", e.getMessage());
        } catch (Exception e) {
            LOGGER.error("Exception occured during connection {}", e.getMessage());
        }

    }
}

To make HTTP Patch request using RestTemplate, below configurations are mandatory, for other HTTP calls you may ignore it.

 @Bean
    public RestTemplate restTemplate() {
        LOGGER.info("restTemplate Bean has bean created");
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory(httpClient);
        RestTemplate restTemplate = new RestTemplate(factory);
        return restTemplate;
    }

You have to add the below dependency in pom.xml to use CloseableHttpClient, and HttpClients.

<dependency>
    <groupId>org.apache.httpcomponents.client5</groupId>
    <artifactId>httpclient5</artifactId>
</dependency>