Create JPA EntityManager without persistence xml configuration file

Question

Is there a way to initialize the EntityManager without a persistence unit defined  Can you give all the required properties to create an entity manager  I need to create the EntityManager from the user s specified values at runtime  Updating the persistence xml and recompiling is not an option   Any idea on how to do this is more than welcomed

User · Answer

Yes you can without using any xml file using spring like this inside a  Configuration class  or its equivalent spring config xml     Bean public LocalContainerEntityManagerFactoryBean emf        properties put  javax persistence jdbc driver   dbDriverClassName       properties put  javax persistence jdbc url   dbConnectionURL       properties put  javax persistence jdbc user   dbUser     if needed      LocalContainerEntityManagerFactoryBean emf   new LocalContainerEntityManagerFactoryBean        emf setPersistenceProviderClass org eclipse persistence jpa PersistenceProvider class     If your using eclipse or change it to whatever you re using     emf setPackagesToScan  com yourpkg      The packages to search for Entities  line required to avoid looking into the persistence xml     emf setPersistenceUnitName SysConstants SysConfigPU       emf setJpaPropertyMap properties       emf setLoadTimeWeaver new ReflectiveLoadTimeWeaver       required unless you know what your doing     return emf

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I was able to create an EntityManager with Hibernate and PostgreSQL purely using Java code  with a Spring configuration  the following    Bean public DataSource dataSource         final PGSimpleDataSource dataSource   new PGSimpleDataSource         dataSource setDatabaseName   mytestdb         dataSource setUser   myuser         dataSource setPassword  mypass         return dataSource      Bean public Properties hibernateProperties        final Properties properties   new Properties         properties put   hibernate dialect    org hibernate dialect PostgreSQLDialect         properties put   hibernate connection driver class    org postgresql Driver         properties put   hibernate hbm2ddl auto    create-drop          return properties      Bean public EntityManagerFactory entityManagerFactory  DataSource dataSource  Properties hibernateProperties        final LocalContainerEntityManagerFactoryBean em   new LocalContainerEntityManagerFactoryBean        em setDataSource  dataSource        em setPackagesToScan   net initech domain         em setJpaVendorAdapter  new HibernateJpaVendorAdapter          em setJpaProperties  hibernateProperties        em setPersistenceUnitName   mytestdomain         em setPersistenceProviderClass HibernatePersistenceProvider class       em afterPropertiesSet         return em getObject        The call to LocalContainerEntityManagerFactoryBean afterPropertiesSet   is essential since otherwise the factory never gets built  and then getObject   returns null and you are chasing after NullPointerExceptions all day long    -   It then worked with the following code   PageEntry pe   new PageEntry    pe setLinkName   Google     pe setLinkDestination  new URL   http   www google com        EntityTransaction entTrans   entityManager getTransaction    entTrans begin    entityManager persist  pe    entTrans commit      Where my entity was this     Entity  Table name    page entries   public class PageEntry         Id      GeneratedValue strategy   GenerationType IDENTITY      private long id       private String linkName      private URL linkDestination          gets  amp  setters omitted

User · Answer

DataNucleus JPA that I use also has a way of doing this in its docs  No need for Spring  or ugly implementation of PersistenceUnitInfo   Simply do as follows  import org datanucleus metadata PersistenceUnitMetaData  import org datanucleus api jpa JPAEntityManagerFactory   PersistenceUnitMetaData pumd   new PersistenceUnitMetaData  dynamic-unit    RESOURCE LOCAL   null   pumd addClassName  mydomain test A    pumd setExcludeUnlistedClasses    pumd addProperty  javax persistence jdbc url    jdbc h2 mem nucleus    pumd addProperty  javax persistence jdbc user    sa    pumd addProperty  javax persistence jdbc password        pumd addProperty  datanucleus schema autoCreateAll    true     EntityManagerFactory emf   new JPAEntityManagerFactory pumd  null

User · Answer

You can also get an EntityManager using PersistenceContext or Autowired annotation  but be aware that it will not be thread-safe   PersistenceContext private EntityManager entityManager

User · Answer

Is there a way to initialize the EntityManager without a persistence unit defined    You should define at least one persistence unit in the persistence xml deployment descriptor      Can you give all the required properties to create an Entitymanager     The name attribute is required  The other attributes and elements are optional   JPA specification   So this should be more or less your minimal persistence xml file     lt persistence gt       lt persistence-unit name   REQUIRED PERSISTENCE UNIT NAME GOES HERE   gt          SOME PROPERTIES      lt  persistence-unit gt   lt  persistence gt       In Java EE environments  the jta-data-source and non-jta-data-source elements are used to specify the global JNDI name of the JTA and or non-JTA data source to be used by the persistence provider    So if your target Application Server supports JTA  JBoss  Websphere  GlassFish   your persistence xml looks like    lt persistence gt       lt persistence-unit name   REQUIRED PERSISTENCE UNIT NAME GOES HERE   gt           lt  --GLOBAL JNDI GOES HERE-- gt           lt jta-data-source gt jdbc myDS lt  jta-data-source gt       lt  persistence-unit gt   lt  persistence gt    If your target Application Server does not support JTA  Tomcat   your persistence xml looks like    lt persistence gt       lt persistence-unit name   REQUIRED PERSISTENCE UNIT NAME GOES HERE   gt           lt  --GLOBAL JNDI GOES HERE-- gt           lt non-jta-data-source gt jdbc myDS lt  non-jta-data-source gt       lt  persistence-unit gt   lt  persistence gt    If your data source is not bound to a global JNDI  for instance  outside a Java EE container   so you would usually define JPA provider  driver  url  user and password properties  But property name depends on the JPA provider  So  for Hibernate as JPA provider  your persistence xml file will looks like    lt persistence gt       lt persistence-unit name   REQUIRED PERSISTENCE UNIT NAME GOES HERE   gt           lt provider gt org hibernate ejb HibernatePersistence lt  provider gt           lt class gt br com persistence SomeClass lt  class gt           lt properties gt               lt property name  hibernate connection driver class  value  org apache derby jdbc ClientDriver   gt               lt property name  hibernate connection url  value  jdbc derby   localhost 1527 EmpServDB create true   gt               lt property name  hibernate connection username  value  APP   gt               lt property name  hibernate connection password  value  APP   gt           lt  properties gt       lt  persistence-unit gt   lt  persistence gt    Transaction Type Attribute     In general  in Java EE environments  a transaction-type of RESOURCE LOCAL assumes that a non-JTA datasource will be provided  In a Java EE environment  if this element is not specified  the default is JTA  In a Java SE environment  if this element is not specified  a default of RESOURCE LOCAL may be assumed     To insure the portability of a Java SE application  it is necessary to explicitly list the managed persistence classes that are included in the persistence unit  JPA specification       I need to create the EntityManager from the user s specified values at runtime   So use this   Map addedOrOverridenProperties   new HashMap        Let s suppose we are using Hibernate as JPA provider addedOrOverridenProperties put  hibernate show sql   true    Persistence createEntityManagerFactory  lt PERSISTENCE UNIT NAME GOES HERE gt   addedOrOverridenProperties

User · Answer

With plain JPA  assuming that you have a PersistenceProvider implementation  e g  Hibernate   you can use the PersistenceProvider createContainerEntityManagerFactory PersistenceUnitInfo info  Map map  method to bootstrap an EntityManagerFactory without needing a persistence xml  However  it s annoying that you have to implement the PersistenceUnitInfo interface  so you are better off using Spring or Hibernate which both support bootstrapping JPA without a persistence xml file  this nativeEntityManagerFactory   provider createContainerEntityManagerFactory      this persistenceUnitInfo       getJpaPropertyMap       Where the PersistenceUnitInfo is implemented by the Spring-specific MutablePersistenceUnitInfo class

User · Answer

Here s a solution without Spring  Constants are taken from org hibernate cfg AvailableSettings     entityManagerFactory   new HibernatePersistenceProvider   createContainerEntityManagerFactory              archiverPersistenceUnitInfo                ImmutableMap  lt String  Object gt builder                        put JPA JDBC DRIVER  JDBC DRIVER                       put JPA JDBC URL  JDBC URL                       put DIALECT  Oracle12cDialect class                       put HBM2DDL AUTO  CREATE                       put SHOW SQL  false                       put QUERY STARTUP CHECKING  false                       put GENERATE STATISTICS  false                       put USE REFLECTION OPTIMIZER  false                       put USE SECOND LEVEL CACHE  false                       put USE QUERY CACHE  false                       put USE STRUCTURED CACHE  false                       put STATEMENT BATCH SIZE  20                       build      entityManager   entityManagerFactory createEntityManager      And the infamous PersistenceUnitInfo   private static PersistenceUnitInfo archiverPersistenceUnitInfo         return new PersistenceUnitInfo              Override         public String getPersistenceUnitName                 return  ApplicationPersistenceUnit                       Override         public String getPersistenceProviderClassName                 return  org hibernate jpa HibernatePersistenceProvider                       Override         public PersistenceUnitTransactionType getTransactionType                 return PersistenceUnitTransactionType RESOURCE LOCAL                      Override         public DataSource getJtaDataSource                 return null                      Override         public DataSource getNonJtaDataSource                 return null                      Override         public List lt String gt  getMappingFileNames                 return Collections emptyList                        Override         public List lt URL gt  getJarFileUrls                 try                   return Collections list this getClass                                                getClassLoader                                                getResources                     catch  IOException e                    throw new UncheckedIOException e                                     Override         public URL getPersistenceUnitRootUrl                 return null                      Override         public List lt String gt  getManagedClassNames                 return Collections emptyList                        Override         public boolean excludeUnlistedClasses                 return false                      Override         public SharedCacheMode getSharedCacheMode                 return null                      Override         public ValidationMode getValidationMode                 return null                      Override         public Properties getProperties                 return new Properties                        Override         public String getPersistenceXMLSchemaVersion                 return null                      Override         public ClassLoader getClassLoader                 return null                      Override         public void addTransformer ClassTransformer transformer                         Override         public ClassLoader getNewTempClassLoader                 return null

[jpa] Create JPA EntityManager without persistence.xml configuration file

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