how to use util concurrent package to replicate the load testing concurrent problems

we have provided some RESTFUL webservices ,where client is going to consume these services.for this we have used spring restful services+JPA.
while doing load testing of 100 or more concurrent users we are facing exceptions like "LockAcquistionException" and
"Unable to commit: transaction marked for rollback". in normal scenarios its working fine but while doing load testing we are getting above exceptions

to replicate these scenarios we used Java Concurrent package and come up with the below code.
can we i use below code so that 100 or 200  users call these service concurrently?my intension is to replicate the scenario thats happening in load testing?

public class RestClientTest  
{
  ExecutorService executor = Executors.newFixedThreadPool(30);
  String	BASE_URL_DOC =null;
  
  
  @Autowired
  RestTemplate restTemplate;
  
  @Test
  public void updateDoc() throws Exception{
    
    try {
    	
    	for(int i = 1; i <= 100; i++) {
            Runnable worker = new MyRunnable(i);
            executor.execute(worker);
        }
        executor.shutdown();
        // Wait until all threads are finish
        while (!executor.isTerminated()) {
 
        }
        System.out.println("\nFinished all threads");
        
   
	} catch (Exception e) {
		e.printStackTrace();
	}

  }
 
  
  public  class MyRunnable implements Runnable {
  
	  private int i;
      MyRunnable(int i) {
          this.i = i;
      }

      public void run() {
    	  
    	  try {
    			   String	BASE_URL_DOC = "http://localhost:8080/docws/updateDocument/"+i+"/13131313";
        		   output= 	 restTemplate.getForObject(BASE_URL_DOC,Response.class);
        	
          } catch (Exception e) {
             e.printStackTrace();
          }
         
      }
  }

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}

//above restful websrevices internally calls this JPA code
************************************************************

@Transactional
public int updateDocument(Long empId, Long docId) {
		
		Query updateDocumentQuery = em.createNamedQuery("updateDocument");
		updateDocumentQuery.setParameter("empId", empId);
		updateDocumentQuery.setParameter("docId", docId);
		int updated = updateDocumentQuery.executeUpdate();
		
		if (updated != 0) {			
			recordHistory(empId, docId);			
		}
		return updated;
	}
	
	private void recordHistory(Long empId, Long docId) {
		Date currentDate = new Date();
		Query historyRecQuery = em.createNamedQuery("getHistoryRecord");
		historyRecQuery.setParameter("empId", empId);
		
		List results = (List) historyRecQuery.getResultList();
		if (!results.isEmpty()) {
			HistoryRecs historyRec = (HistoryRecs) results.get(0);
			historyRec.setEndDate(currentDate);
			em.persist(historyRec);
		}
		Employee emp = em.find(Employee.class, empId); //some times here we are getting LockAcquistionException here
		
		
		HistoryRecs historyRecs = new HistoryRecs();
		historyRecs.setEmpId(empId);
		historyRecs.setDocId(docId);		
		if(emp.getpath() != null){
			historyRecs.setpath(emp.getpath());
		}
		
		historyRecs.setFromDate(currentDate);
		em.persist(historyRecs);
	}

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