Package pl.morgwai.base.servlet.guiced.jpa

Class JpaServlet

java.lang.Object

jakarta.servlet.GenericServlet

jakarta.servlet.http.HttpServlet

pl.morgwai.base.servlet.guiced.jpa.JpaServlet

All Implemented Interfaces:

Servlet, ServletConfig, Serializable

Direct Known Subclasses:

SimpleAsyncJpaServlet

public abstract class JpaServlet
extends HttpServlet

Base class for servlets that perform other types of time consuming operations apart from JPA. Requests injection of a Provider<EntityManager>, its associated jpaExecutor and provides some related helper methods: executeWithinTx(Callable), removeEntityManagerFromRequestScope().

See Also:

SimpleAsyncJpaServlet, Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
protected ContextTracker<ContainerCallContext>	containerCallContextTracker
protected jakarta.inject.Provider<EntityManager>	entityManagerProvider	Provides request scoped EntityManager instances.
protected ContextTrackingExecutor	jpaExecutor	Executor associated with entityManagerProvider's persistence unit.

Constructor Summary

Constructors

Constructor	Description
JpaServlet()

Method Summary

Modifier and Type	Method	Description
static <T> T	executeWithinTx(jakarta.inject.Provider<EntityManager> entityManagerProvider, Callable<T> operation)	Executes operation within the DB transaction obtained from entityManagerProvider.
protected <T> T	executeWithinTx(Callable<T> operation)	Executes operation within the DB transaction obtained from entityManagerProvider.
protected String	getPersistenceUnitBindingName()	Returns injection binding name for entityManagerProvider and jpaExecutor in apps that use multiple persistence units.
void	init(ServletConfig config)	Requests instances of entityManagerProvider and jpaExecutor from Guice.
void	removeEntityManagerFromRequestScope()	Removes the stored EntityManager from the scope of the current request.

Methods inherited from class jakarta.servlet.http.HttpServlet

doDelete, doGet, doHead, doOptions, doPost, doPut, doTrace, getLastModified, service, service

Methods inherited from class jakarta.servlet.GenericServlet

destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

entityManagerProvider

protected jakarta.inject.Provider<EntityManager> entityManagerProvider

Provides request scoped EntityManager instances.

If a given app uses multiple persistence units, this provider will use the one indicated by getPersistenceUnitBindingName().

jpaExecutor

protected ContextTrackingExecutor jpaExecutor

Executor associated with entityManagerProvider's persistence unit.

In apps that use a single persistence unit, this is the same instance as JpaServletContextListener.mainJpaExecutor. Otherwise, the one indicated by getPersistenceUnitBindingName().

containerCallContextTracker

@Inject
protected ContextTracker<ContainerCallContext> containerCallContextTracker

Constructor Detail

JpaServlet

public JpaServlet()

Method Detail

getPersistenceUnitBindingName

protected String getPersistenceUnitBindingName()

Returns injection binding name for entityManagerProvider and jpaExecutor in apps that use multiple persistence units.

If the app uses a single persistence unit (default, JpaServletContextListener.isSinglePersistenceUnitApp() is not overridden and returns true) then this method is never used.

By default returns JpaServletContextListener.MAIN_PERSISTENCE_UNIT_BINDING_NAME.
If an app that uses multiple persistence units needs to use persistence unit other than the main in some servlet, then this method should be overridden accordingly in that servlet.

init

public void init(ServletConfig config)
          throws ServletException

Requests instances of entityManagerProvider and jpaExecutor from Guice.

Specified by:

init in interface Servlet

Overrides:

init in class GenericServlet

Throws:

ServletException

executeWithinTx

protected <T> T executeWithinTx(Callable<T> operation)
                         throws Exception

Executes operation within the DB transaction obtained from entityManagerProvider. If operation completes normally, commits the transaction. Otherwise the transaction is rolled back.

Throws:

Exception

executeWithinTx

public static <T> T executeWithinTx(jakarta.inject.Provider<EntityManager> entityManagerProvider,
                                    Callable<T> operation)
                             throws Exception

Executes operation within the DB transaction obtained from entityManagerProvider. If operation completes normally, commits the transaction. Otherwise the transaction is rolled back.

Throws:

Exception

removeEntityManagerFromRequestScope

public void removeEntityManagerFromRequestScope()

Removes the stored EntityManager from the scope of the current request.

If a given app performs some time consuming operations (such as network communication long CPU/GPU intensive computations etc), that need to be surrounded by JPA operations that do not need to be a part of the same transaction, like for example:

 List someRecords = someDbDao.getSomeDataFromDB(); // TX-1 or no TX
 SomeClass results = someExternalNetworkConnector.someLongOperation(someRecords);
 someDbDao.storeSomeStatsAboutResults(results); // TX-2

then it may significantly improve performance to close the EntityManager after the first (batch of) JPA operation(s) so that other requests may use the underlying connection in the mean time.
In such case, for the second (batch of) JPA operation(s) a new EntityManager must be obtained. To prevent request-scoped entityManagerProvider from reusing the old closed one, it needs to be removed from the scope.

Note: If a request is handled by multiple threads, care must be taken to prevent some of them from retaining the old stale instance.