Using parallel stream inside Spring batch process

Question

World. We are using spring batch to read from a table (Message), and write the modifications on the table (Site), the functionality is working perfectly, but when am having more than 1000 Site to modify for a single Message, the process is taking too long.

To reduce the processing time, I used multiThreading inside the Process of the batch.

But am having an entity detached error.

• the batch processor (updateSite change the values of the Site based on the Message data, but it does not save the entities)

  public DataWrapper process(MessageZbusOras messageZbusOras) {
      List<Site> sites = siteService.getSites(messageZbusOras);        
      sites.parallelStream().forEach(site -> {
          updateSite(messageZbusOras,site);
      });
      return new DataWrapper(messageZbusOras);
  }
  

• the batch writer

  public void write(List<? extends DataWrapper> items) throws Exception {
      List<MessageZbusOras> messageZbusOras = new ArrayList<>();
      for (DataWrapper wrapper : items) {
          messageZbusOras.add(wrapper.getMessageZbusOras());
      }
      messageZbusOrasRepository.saveAll(messageZbusOras);
      messageZbusOrasRepository.flush();
  }
  

Apparently, the error occur when the site toked by another thread, automaticly it is detached from Hibernate session, so I can't flush the modification in the writer.

RefEvtLibelleCommentaire is an entity linked to Site by LazyInit.

If you need more clarifications please ask me.