The way to run Hibernate is to create a SessionFactory object. The SessionFactory Object is responsible for providing us with Hibernate sessions to perform the various db Operations. In minimal words, the Session factory is responsible for internally managing all db related operations for us.
Before using a session factory it has to be configured for use.
For this a Configuration object is used. There are two (standard or commonly used )ways of creating the Configuration object -
Now to create the more common hibernate.cfg.xml file.
On Execution of Line 1:
NOTE: No attempt is made to set up any connection with database yet.
On Execution of Line 2:
If the file is found it will load and read it and override any mappings that were read from the properties file.Thus the invalid connection details that we have specified in the properties file will not be used for any db connections. Instead the values specified in the cfg file will be used. Also the mapping documents specified in the cfg file are loaded and read.
The fields in the Java Objects are mapped to the columns in the table ( all based on details in the mapping files. There is no contact with database yet).
In the last Line the session factory is declared as being configured and ready for use. Thus we can observe that :
There is another ways to provide setting options to the Configuration object - via code.
For this a Configuration object is used. There are two (standard or commonly used )ways of creating the Configuration object -
- via a properties file
- via an XML Configuration.
Configuration configuration = new Configuration(); //Line 1 configuration = configuration.configure(); //Line 2 SessionFactory sessionFactory = configuration.buildSessionFactory();Before running this code, I also added a sample hibernate.properties to the project class path.
hibernate.connection.driver_class = org.postgresql.Driver hibernate.connection.url = jdbc:mysql://localhost:3306/menagerieDb hibernate.connection.username = nonExistingUser hibernate.connection.password = invalidPwd hibernate.dialect = org.hibernate.dialect.MySQLDialect hibernate.show_sql=true hibernate.format_sql=trueThe username and password seen above are invalid. If Hibernate were to be used with these it would never get a database connection.
Now to create the more common hibernate.cfg.xml file.
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="hibernate.connection.username">root</property> <property name="hibernate.connection.password">root</property> <property name="hibernate.connection.url"> jdbc:mysql://localhost:3306/menagerieDb</property> <property name="hibernate.hbm2ddl.auto">validate</property> <property name="show_sql">true</property> <mapping resource="com/menagerie/domain/entity/Owner.hbm.xml" /> <mapping resource="com/menagerie/domain/entity/Pet.hbm.xml" /> </session-factory> </hibernate-configuration>The cfg file holds valid credentials. I now executed the code and decided to trace the logs generated.
On Execution of Line 1:
0 [main] INFO org.hibernate.cfg.Environment - Hibernate 3.2.5
1 [main] INFO org.hibernate.cfg.Environment - loaded properties from
resource hibernate.properties: {hibernate.connection.username=nonExistingUser,
hibernate.connection.password=**********,
hibernate.dialect=org.hibernate.dialect.MySQLDialect,
hibernate.connection.url=jdbc:mysql://localhost:3306/menagerieDb
hibernate.bytecode.use_reflection_optimizer=false,
hibernate.connection.driver_class=org.postgresql.Driver}
2 [main] INFO org.hibernate.cfg.Environment - Bytecode provider name : cglib
4 [main] INFO org.hibernate.cfg.Environment - using JDK 1.4
java.sql.Timestamp handling
When a Configuration object is created, it searches in the class path for the
default configuration file(hibernate.properties). If it finds hibernate.properties, it
loads the
properties from this file. NOTE: No attempt is made to set up any connection with database yet.
On Execution of Line 2:
51 [main] INFO org.hibernate.cfg.Configuration - configuring from resource: / hibernate.cfg.xml 51 [main] INFO org.hibernate.cfg.Configuration - Configuration resource: /hibernate.cfg.xml 92 [main] DEBUG org.hibernate.util.DTDEntityResolver - trying to resolve system-id [http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd] 93 [main] DEBUG org.hibernate.util.DTDEntityResolver - recognized hibernate namespace; attempting to resolve on classpath under org /hibernate/ 93 [main] DEBUG org.hibernate.util.DTDEntityResolver - located [ http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd] in classpath 108 [main] DEBUG org.hibernate.cfg.Configuration - connection.driver_class=com.mysql.jdbc.Driver 109 [main] DEBUG org.hibernate.cfg.Configuration - dialect=org.hibernate.dialect.MySQLDialect 109 [main] DEBUG org.hibernate.cfg.Configuration - hibernate.connection.username=root 109 [main] DEBUG org.hibernate.cfg.Configuration - hibernate.connection.password=root 109 [main] DEBUG org.hibernate.cfg.Configuration - hibernate.connection.url=jdbc:mysql://localhost:3306/menagerieDb 109 [main] DEBUG org.hibernate.cfg.Configuration - hibernate.generate_statistics=false 109 [main] DEBUG org.hibernate.cfg.Configuration - show_sql=true 109 [main] DEBUG org.hibernate.cfg.Configuration - hibernate.cache.use_structured_entries=false 109 [main] DEBUG org.hibernate.cfg.Configuration - hibernate.cache.use_second_level_cache=false 110 [main] DEBUG org.hibernate.cfg.Configuration - null<-org.dom4j.tree.DefaultAttribute@4741d6 [ Attribute: name resource value "com/menagerie/domain/entity/Owner.hbm.xml"] 110 [main] INFO org.hibernate.cfg.Configuration - Reading mappings from resource : com/menagerie/domain/entity/Owner.hbm.xml 111 [main] DEBUG org.hibernate.util.DTDEntityResolver - trying to resolve system-id [http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd] 111 [main] DEBUG org.hibernate.util.DTDEntityResolver - recognized hibernate namespace; attempting to resolve on classpath under org/hibernate/ 111 [main] DEBUG org.hibernate.util.DTDEntityResolver - located [ http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd] in classpath 168 [main] INFO org.hibernate.cfg.HbmBinder - Mapping class: com.menagerie.domain.entity.Owner -> OWNER 172 [main] DEBUG org.hibernate.cfg.HbmBinder - Mapped property: id -> ID ..... 181 [main] DEBUG org.hibernate.cfg.Configuration - null<-org.dom4j.tree. DefaultAttribute@922804 [ Attribute: name resource value "com/menagerie/domain/entity/Pet.hbm.xml"] 181 [main] INFO org.hibernate.cfg.Configuration - Reading mappings from resource : com/menagerie/domain/entity/Pet.hbm.xml 182 [main] DEBUG org.hibernate.util.DTDEntityResolver - trying to resolve system-id [http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd] 182 [main] DEBUG org.hibernate.util.DTDEntityResolver - recognized hibernate namespace; attempting to resolve on classpath under org/hibernate/ 182 [main] DEBUG org.hibernate.util.DTDEntityResolver - located [ http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd] in classpath 194 [main] INFO org.hibernate.cfg.HbmBinder - Mapping class: com.menagerie.domain.entity.Pet -> PET 195 [main] DEBUG org.hibernate.cfg.HbmBinder - Mapped property: id -> ID 195 [main] DEBUG org.hibernate.cfg.HbmBinder - Mapped property: name -> NAME .... 233 [main] INFO org.hibernate.cfg.Configuration - Configured SessionFactory: null [NOTE: Certain Logs have been removed for readability]When the call is made to configure the newly created Configuration object, it searched for the configuration file hibernate.cfg.xml on the class-path.
If the file is found it will load and read it and override any mappings that were read from the properties file.Thus the invalid connection details that we have specified in the properties file will not be used for any db connections. Instead the values specified in the cfg file will be used. Also the mapping documents specified in the cfg file are loaded and read.
The fields in the Java Objects are mapped to the columns in the table ( all based on details in the mapping files. There is no contact with database yet).
In the last Line the session factory is declared as being configured and ready for use. Thus we can observe that :
- Hibernate gives precedence to xml configuration over the property files approach.
- In case the xml file is not present then Hibernate will use the values detected in the hibernate.properties.
- The xml files also allows you to specify the mapping documents.
- It is not necessary that the xml file used must have the name "hibernate.cfg.xml". An alternative file can also be provided eg :
configuration = configuration.configure("/options/hib.cfg.xml");
public static void main(String[] args) { new Configuration().configure().setProperty("show_sql", "false") .addResource("com/menagerie/domain/entity/Pet.hbm.xml") .addResource("com/menagerie/domain/entity/Owner.hbm.xml") .buildSessionFactory(); }Using this it is possible to set all configurations via code (Not a nice way though)
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