#forkjoinpool

Many of you have gone through google to find out on how to use ForkJoinPool for many use cases. But it’s hard to find the use case for a DB query. Here’s the simple example on how to use it.

Create a Recursive Task class like the following.

public class MongoQueryForkJoinTask<T> extends RecursiveTask<List<T>> {

   private final int pageSize;    private int pageIndex;    private final Long totalCount;    private final Query query;    private final MongoTemplate mongoTemplate;    private final Class clazz;

   private static final Logger LOG = Logger.getLogger(MongoQueryForkJoinTask.class);

   public MongoQueryForkJoinTask(int pageSize, int pageIndex, Long totalCount, Query query, MongoTemplate mongoTemplate, Class clazz) {        this.pageSize = pageSize;        this.pageIndex = pageIndex;        this.totalCount = totalCount;        this.query = query;        this.mongoTemplate = mongoTemplate;        this.clazz = clazz;    }

   @Override    protected List<T> compute() {        if(totalCount <= pageSize ){            LOG.info("Fetching records for Class ["+clazz.getSimpleName()+"] with pageSize ["+pageSize+"] and pageIndex ["+pageIndex+"], totalCount ["+totalCount+"]");            Pageable pageRequest = new PageRequest(pageIndex, pageSize);            query.with(pageRequest);            return mongoTemplate.find(query, clazz);        }        List<T> returnList  = new ArrayList<>();        LOG.info("Executing all the tasks...");        for (int i=0;i<pageIndex;i++){            final MongoQueryForkJoinTask<T> task = new MongoQueryForkJoinTask<>(pageSize, i, Long.valueOf(pageSize), query,  mongoTemplate, clazz);            task.fork();            returnList.addAll(task.join());        }        return returnList;    } }

And use the same task to invoke via ForkJoinPool.

pool.invoke(new MongoQueryForkJoinTask<Employee>(1000, 10000, count, q, mongoTemplate, Employee.class));

Where q is the Mongo Query that we construct as per our requirements.