implement multithreading while calling method to update record through API in springboot

I am writing an application in Springboot to fetch records from a database and then call an external rest api to update records into some other table. This code is completed and working as expected. As I need to improve performance as well. I am trying implement mulithreading while calling API, so that I can send multiple records at a time.

Structure :

Fetch records from a table and Store it in a list ---> Loop over list ---> multi threaded call to API

ProvRecordProcessing.java : This call will fetch records from database and create a list and call to ProvRecordService.java
ProvRecordService.java : This call will handle all API logic..

After some research, I tried to implement below to make it multithreaded :

1. Make ProvRecordService class to implement Runnable and override void run method
2. Instead of calling method, calling executorService.execute(new ProvRecordService(record));

ProvRecordProcessing.java :

I have removed other business logic from the code, only keep part where calling API method..

  @Component 
public class ProvRecordProcessing {
.....Code to fetch records from database....
List<UpdateProvider> provRecords = jdbcTemplate.query(sqlApiSelectQuery, new ProvRecordMapper());
//added for multithreading
ExecutorService executorService = Executors.newFixedThreadPool(2);
//looping over list records and calling API to process records
for(UpdateProvider record : provRecords) {
executorService.execute(new ProvRecordService(record));
}  
executorService.shutdown();  		
}
}

ProvRecordService.java

Just to make it multithreaded, I have added few sections in the below code with comment : //added for multithreading

package com.emerald.paymentengineapi.service;
import java.security.KeyManagementException;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import java.util.List;
import javax.sql.DataSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@Service
public class ProvRecordService implements IFxiProviderService, Runnable {
@Autowired
RestSslException restSslTemplate;
@Autowired
DbConfig dbConfig;
@Autowired
UpdateProvider updateProvider; // added for multithreading
@Autowired
JdbcTemplate jdbcTemplate;
@Autowired
TokenService tokenService;
@Value("${SHIELD_API_URL}")
private String SHIELD_API_URL;
@Value("${token_expire_time}")
private String token_expire;
RestTemplate restTemplate;
DataSource dataSource;
UpdateProvider record; // added for multithreading
Logger logger = LoggerFactory.getLogger(ProvRecordService.class);
private static String FETCH_OPTIONS_SQL = "select OPTION_NAME, OPTION_VALUE from FSG.FSG_PRCB_PE_API_REQ_CONFIG";
public ProvRecordService(UpdateProvider record) { // added for multithreading
// TODO Auto-generated constructor stub
this.record = record;
}
@Override
public void run() { // added for multithreading
updateProvider(record);
}
@Scheduled(fixedRateString = "token_expire")
public ResponseEntity<String> runTokenScheduler() throws KeyManagementException, KeyStoreException, NoSuchAlgorithmException {
logger.info("Fetching Token..." + token_expire);
ResponseEntity<String> response = tokenService.getOauth2Token();
return response;
}
@Override
public ResponseEntity<String> updateProvider(UpdateProvider updateProviderRequest) {
dataSource = dbConfig.dataSource();
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
try {
restTemplate = restSslTemplate.restTemplate();
} catch (KeyManagementException | KeyStoreException | NoSuchAlgorithmException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
ResponseEntity<String> response = null;
try {
if (null == TokenService.TOKEN_VALUE.get(ConfigConstants.ACCESS_TOKEN))
runTokenScheduler();
HttpHeaders headers = new HttpHeaders();
headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
System.out.println("value :" + TokenService.TOKEN_VALUE.get(ConfigConstants.TOKEN_TYPE));
System.out.println("access_token :" + TokenService.TOKEN_VALUE.get(ConfigConstants.ACCESS_TOKEN));
headers.add(ConfigConstants.AUTHORIZATION, TokenService.TOKEN_VALUE.get(ConfigConstants.TOKEN_TYPE) + " "
+ TokenService.TOKEN_VALUE.get(ConfigConstants.ACCESS_TOKEN));
headers.add(ConfigConstants.CLIENT_CODE, ConfigConstants.CSP_PROVIDER_BATCH);
List<RequestOptions> customers = jdbcTemplate.query(FETCH_OPTIONS_SQL,new BeanPropertyRowMapper(RequestOptions.class));
updateProviderRequest.getXpfRequestData().setRequestOptions(customers);
HttpEntity<UpdateProvider> entity = new HttpEntity<UpdateProvider>(updateProviderRequest, headers);
response = restTemplate.exchange(SHIELD_API_URL, HttpMethod.PUT, entity, String.class);
if (response.getStatusCode() == HttpStatus.NO_CONTENT) {
logger.info(updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getTaxId());
logger.info(updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getProviderId());
updateStatusInDB(String.valueOf(response.getStatusCodeValue()), "NO_CONTENT",
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getTaxId(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getProviderId());
logger.info("Provider has been updated successfully");
} else if (response.getStatusCode() == HttpStatus.INTERNAL_SERVER_ERROR) {
updateStatusInDB(String.valueOf(response.getStatusCodeValue()), "INTERNAL_SERVER_ERROR",
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getTaxId(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getProviderId());
logger.error("Internal Server error occures");
} else if (response.getStatusCode() == HttpStatus.NOT_FOUND) {
updateStatusInDB(String.valueOf(response.getStatusCodeValue()), "NOT_FOUND",
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getTaxId(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getProviderId());
logger.error("Provider not found");
}
} catch (TokenServiceException ex) {
logger.error("Exception occures in calling Token API");
updateStatusInDB(ex.getMessage(), ex.getLocalizedMessage(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getTaxId(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getProviderId());
//throw new RuntimeException("Exception occures in API " + ex);
} catch (HttpClientErrorException ex) {
logger.error("HttpClientErrorException occures in calling API");
updateStatusInDB(ex.getStatusText(), ex.getStatusText(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getTaxId(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getProviderId());
//throw new HttpClientErrorException(ex.getStatusCode(), ex.getStatusText());
} catch (Exception ex) {
logger.error("Exception occures in calling API");
updateStatusInDB(ex.getMessage(), ex.getMessage(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getTaxId(),
updateProviderRequest.getXpfRequestData().getGroupRecord().getProviderData().getProviderId());
//throw new RuntimeException("Exception occures in API " + ex);
}
return response;
}
private int updateStatusInDB(String errorCode, String errorMessage, String taxId, String providerId) {
return jdbcTemplate.update(
"update FSG_WRK.FSG_PRCB_PE_API_REQUEST set ERRORCODE = ?, ERRORMESSAGE = ? where TAXID = ? and PROVIDERID= ?",
errorCode, errorMessage, taxId, providerId);
}
}

I debug this code , and it's going void run method and record is also getting populated , but after that, it's not going into the updateProvider method for processing and I am getting below error :

 Exception in thread "pool-2-thread-1" java.lang.NullPointerException
at com.emerald.paymentengineapi.service.ProvRecordService.updateProvider(ProvRecordService.java:92)
at com.emerald.paymentengineapi.service.ProvRecordService.run(ProvRecordService.java:78)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Exception in thread "pool-2-thread-2" java.lang.NullPointerException
at com.emerald.paymentengineapi.service.ProvRecordService.updateProvider(ProvRecordService.java:92)
at com.emerald.paymentengineapi.service.ProvRecordService.run(ProvRecordService.java:78)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Exception in thread "pool-2-thread-3" java.lang.NullPointerException
at com.emerald.paymentengineapi.service.ProvRecordService.updateProvider(ProvRecordService.java:92)
at com.emerald.paymentengineapi.service.ProvRecordService.run(ProvRecordService.java:78)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Exception in thread "pool-2-thread-5" java.lang.NullPointerException
at com.emerald.paymentengineapi.service.ProvRecordService.updateProvider(ProvRecordService.java:92)
at com.emerald.paymentengineapi.service.ProvRecordService.run(ProvRecordService.java:78)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)

Update :

After more debugging, I got to know, the issue is occurring on the below line :

dataSource = dbConfig.dataSource();
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);

I am trying to set dataSource here and this was working fine, when I haven't added code for multithreading. I am not able to get the reason. Please suggest.

The code is wrong here:

1. There is no point to create new ExecutorService per request execution.

a better approach would be creating it only once and keeping it as a data field of the ProvRecordProcessing component. Creating threads is expensive + in your approach, you don't know how many threads can be created simultaneously (what if this method is called by many users in parallel - if each creates thread pool you it can be really expensive).

In addition to the above if you use the thread pool executor you should ideally close it when the application shuts down, so don't forget to call close on predestroy or something.

2. Don't create a service with a new keyword, Spring won't be able to manage it and won't "process" any annotation of it (Autowired, Value, etc), so this code is wrong:

     for(UpdateProvider record : provRecords) {
executorService.execute(new ProvRecordService(record));
}  

Instead, Inject the service into ProvRecordProcessing Component as a singleton and call its method responsible for sending http request from runnable / callable. Here is a schematic example of what I mean:

@Component
class ProvRecordProcessing {
@Autowired
private ProvRecordService provRecordService;
....
for(UpdateProvider record : provRecords) {
executorService.execute(() -> provRecordService.updateHttpOrWhatever(record));
}
} 

With this approach, ProvRecordService becomes a regular spring managed bean.

There are more advanced solutions for this, namely using @Async methods that can eliminate the need to "manually" maintain the thread pool. See This tutorial for example... Since you haven't shown those in a question, I assume it's beyond the scope of what you're asking so just keep in mind that it also exists. Of course, if you implement your code right it will do just fine.