Class JpaPagingItemReader<T>

All Implemented Interfaces:
ItemReader<T>, ItemStream, ItemStreamReader<T>, org.springframework.beans.factory.InitializingBean

public class JpaPagingItemReader<T> extends AbstractPagingItemReader<T>

ItemReader for reading database records built on top of JPA.

It executes the JPQL setQueryString(String) to retrieve requested data. The query is executed using paged requests of a size specified in AbstractPagingItemReader.setPageSize(int). Additional pages are requested when needed as method is called, returning an object corresponding to current position.

The performance of the paging depends on the JPA implementation and its use of database specific features to limit the number of returned rows.

Setting a fairly large page size and using a commit interval that matches the page size should provide better performance.

In order to reduce the memory usage for large results the persistence context is flushed and cleared after each page is read. This causes any entities read to be detached. If you make changes to the entities and want the changes persisted then you must explicitly merge the entities.

The reader must be configured with an EntityManagerFactory. All entity access is performed within a new transaction, independent of any existing Spring managed transactions.

The implementation is thread-safe in between calls to, but remember to use saveState=false if used in a multi-threaded client (no restart available).

Thomas Risberg, Dave Syer, Will Schipp, Mahmoud Ben Hassine
  • Constructor Details

    • JpaPagingItemReader

      public JpaPagingItemReader()
  • Method Details

    • setEntityManagerFactory

      public void setEntityManagerFactory(jakarta.persistence.EntityManagerFactory entityManagerFactory)
    • setParameterValues

      public void setParameterValues(Map<String,Object> parameterValues)
      The parameter values to be used for the query execution.
      parameterValues - the values keyed by the parameter named used in the query string.
    • setTransacted

      public void setTransacted(boolean transacted)
      By default (true) the EntityTransaction will be started and committed around the read. Can be overridden (false) in cases where the JPA implementation doesn't support a particular transaction. (e.g. Hibernate with a JTA transaction). NOTE: may cause problems in guaranteeing the object consistency in the EntityManagerFactory.
      transacted - indicator
    • afterPropertiesSet

      public void afterPropertiesSet() throws Exception
      Description copied from class: AbstractPagingItemReader
      Check mandatory properties.
      Specified by:
      afterPropertiesSet in interface org.springframework.beans.factory.InitializingBean
      afterPropertiesSet in class AbstractPagingItemReader<T>
      See Also:
      • InitializingBean.afterPropertiesSet()
    • setQueryString

      public void setQueryString(String queryString)
      queryString - JPQL query string
    • setQueryProvider

      public void setQueryProvider(JpaQueryProvider queryProvider)
      queryProvider - JPA query provider
    • doOpen

      protected void doOpen() throws Exception
      Description copied from class: AbstractItemCountingItemStreamItemReader
      Open resources necessary to start reading input.
      doOpen in class AbstractPagingItemReader<T>
      Exception - Allows subclasses to throw checked exceptions for interpretation by the framework
    • doReadPage

      protected void doReadPage()
      Specified by:
      doReadPage in class AbstractPagingItemReader<T>
    • doClose

      protected void doClose() throws Exception
      Description copied from class: AbstractItemCountingItemStreamItemReader
      doClose in class AbstractPagingItemReader<T>
      Exception - Allows subclasses to throw checked exceptions for interpretation by the framework