Getting Database connection in pure JPA setup

Question

We have a JPA application  using hibernate  and we need to pass a call to a legacy reporting tool that needs a JDBC database connection as a parameter  Is there a simple way to get access to the JDBC connection hibernate has setup

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Here is a code snippet that works with Hibernate 4 based on Dominik s answer  Connection getConnection         Session session   entityManager unwrap Session class       MyWork myWork   new MyWork        session doWork myWork       return myWork getConnection       private static class MyWork implements Work        Connection conn        Override     public void execute Connection arg0  throws SQLException           this conn   arg0             Connection getConnection             return conn

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The word pure doesn t match to the word hibernate   EclipseLink   Getting a JDBC Connection from an EntityManager   It s somewhat straightforward as described in above link    Note that the EntityManager must be joined to a Transaction or the unwrap method will return null   Not a good move at all   I m not sure the responsibility of closing the connection       --------------------------------------------------------- EclipseLink try       final Connection connection   manager unwrap Connection class       if  connection    null       manage is not in any transaction         return function apply connection           catch  final PersistenceException pe        logger log FINE  pe     - gt   failed to unwrap as a connection        Hibernate  It should be  basically  done with following codes      using vendor specific APIs final Session session    Session  manager unwrap Session class     return session doReturningWork lt R gt  function  apply   return session doReturningWork new ReturningWork lt R gt           Override public R execute final Connection connection            return function apply connection               Well  we  at least I  might don t want any vendor-specific dependencies  Proxy comes in rescue   try          See  You shouldn t fire me  ass hole        final Class lt   gt  sessionClass               Class forName  org hibernate Session        final Object session   manager unwrap sessionClass       final Class lt   gt  returningWorkClass               Class forName  org hibernate jdbc ReturningWork        final Method executeMethod               returningWorkClass getMethod  execute   Connection class       final Object workProxy   Proxy newProxyInstance              lookup   lookupClass   getClassLoader                new Class   returningWorkClass                proxy  method  args  - gt                    if  method equals executeMethod                         final Connection connection    Connection  args 0                       return function apply connection                                     return null                      final Method doReturningWorkMethod   sessionClass getMethod               doReturningWork   returningWorkClass       return  R  doReturningWorkMethod invoke session  workProxy     catch  final ReflectiveOperationException roe        logger log Level FINE  roe     - gt   failed to work with hibernate        OpenJPA   Runtime Access to DataSource OPENJPA-1803 Unwrap EntityManager to Connection   I m not sure OpenJPA already serves a way using unwrap Connection class  but can be done with the way described in one of above links   It s not clear the responsibility of closing the connection  The document  one of above links  seems saying clearly but I m not good at English   try       final Class lt   gt  k   Class forName               org apache openjpa persistence OpenJPAEntityManager        if  k isInstance manager             final Method m   k getMethod  getConnection            try               try  Connection c    Connection  m invoke manager                     return function apply c                           catch  final SQLException sqle                logger log FINE  sqle     - gt   failed to work with openjpa                      catch  final ReflectiveOperationException roe        logger log Level FINE  roe     - gt   failed to work with openjpa

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Since the code suggested by  Pascal is deprecated as mentioned by  Jacob  I found this another way that works for me   import org hibernate classic Session  import org hibernate connection ConnectionProvider  import org hibernate engine SessionFactoryImplementor   Session session    Session  em getDelegate    SessionFactoryImplementor sfi    SessionFactoryImplementor  session getSessionFactory    ConnectionProvider cp   sfi getConnectionProvider    Connection connection   cp getConnection

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Hibernate 4   5    Session session   entityManager unwrap Session class   session doWork connection - gt  doSomeStuffWith connection

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Below is the code that worked for me   We use jpa 1 0  Apache openjpa implementation   import java sql Connection  import org apache openjpa persistence OpenJPAEntityManager  import org apache openjpa persistence OpenJPAPersistence   public final class MsSqlDaoFactory            public static final Connection getConnection final EntityManager entityManager                  OpenJPAEntityManager openJPAEntityManager   OpenJPAPersistence cast entityManager                 Connection connection    Connection  openJPAEntityManager getConnection                  return connection

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I ran into this problem today and this was the trick I did  which worked for me      EntityManagerFactory emf   Persistence createEntityManagerFactory  DAOMANAGER       EntityManagerem   emf createEntityManager        org hibernate Session session     EntityManagerImpl  em  getSession       java sql Connection connectionObj   session connection      Though not the best way but does the job

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Hibernate uses a ConnectionProvider internally to obtain connections  From the hibernate javadoc      The ConnectionProvider interface is not intended to be exposed to the application  Instead it is used internally by Hibernate to obtain connections    The more elegant way of solving this would be to create a database connection pool yourself and hand connections to hibernate and your legacy tool from there

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If you are using JAVA EE 5 0  the best way to do this is to use the  Resource annotation to inject the datasource in an attribute of a class  for instance an EJB  to hold the datasource resource  for instance an Oracle datasource  for the legacy reporting tool  this way    Resource mappedName  jdbc  OracleDefaultDS   DataSource datasource    Later you can obtain the connection  and pass it to the legacy reporting tool in this way   Connection conn   dataSource getConnection

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As per the hibernate docs here       Connection   connection         Deprecated   scheduled for removal in 4 x   Replacement depends on need  for doing direct JDBC stuff use   doWork org hibernate jdbc Work        Use Hibernate Work API instead   Session session   entityManager unwrap Session class   session doWork new Work           Override     public void execute Connection connection  throws SQLException              do whatever you need to do with the connection

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if you use EclipseLink  You should be in a JPA transaction to access the Connection  entityManager getTransaction   begin    java sql Connection connection   entityManager unwrap java sql Connection class       entityManager getTransaction   commit

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I m using a old version of Hibernate  3 3 0  with a newest version of OpenEJB  4 6 0   My solution was   EntityManagerImpl entityManager    EntityManagerImpl em getDelegate    Session session   entityManager getSession    Connection connection   session connection    Statement statement   null  try       statement   connection createStatement        statement execute sql       connection commit      catch  SQLException e        throw new RuntimeException e       I had an error after that    Commit can not be set while enrolled in a transaction   Because this code above was inside a EJB Controller  you can t commit inside a transaction   I annotated the method with  TransactionAttribute value   TransactionAttributeType NOT SUPPORTED  and the problem was gone

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Where you want to get that connection is unclear  One possibility would be to get it from the underlying Hibernate Session used by the EntityManager  With JPA 1 0  you ll have to do something like this   Session session    Session em getDelegate    Connection conn   session connection      Note that the getDelegate   is not portable  the result of this method is implementation specific  the above code works in JBoss  for GlassFish you d have to adapt it - have a look at Be careful while using EntityManager getDelegate     In JPA 2 0  things are a bit better and you can do the following   Connection conn   em unwrap Session class  connection      If you are running inside a container  you could also perform a lookup on the configured DataSource

[java] Getting Database connection in pure JPA setup

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