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Hibernate Access Multiple Databases

Author: Yang

Source: http://blog.sina.com.cn/u/1237288325

First, Hibernate is loaded when accessing the database

For most friends using Hibernate, usually use the way to get the Configuration instance: Configuration Configure = New Configuration (). Configure ();

In Hibernate, Configuration is the entrance to Hibernate. When instantification of a Configuration, Hibernate automatically looks for the Hibernate Profile Hibernate.properties in the Environment Variable (ClassPath). If this file exists, load the content of the file into a Properties Example Global_Properties, if not, you will print information hibernate.properties not found;

Next, Hibernate adds all system environment variables (System.getProperties ()) to global_properties. If the configuration file hibernate.properties exists, the system will further verify the validity of this file configuration. For some unsupported configuration parameters, the system will print a warning message.

By default, the configure () method automatically looks for the Hibernate.cfg.xml under the Environment Variable (ClassPath). If the file does not exist, the system will print the following information and throw HibernateException: hibernate.cfg.xml Not found If the file exists, the configure () method will first access , and get the properties of the element Name. If the NAME's attribute is non-empty, this configuration will be used to overwrite Hibernate.Session_Factory_Name of Hibernate.properties. The configured value, from here we can see that configuration information in hibernate.cfg.xml can overwrite configuration information for hibernate.properties.

Next, the configure () method accesses the child elements of , first use all of the element configurations to overwrite the corresponding configuration information in Hibernate.properties.

Then Configure () will access the content of the following elements in turn.

Where is essential, you must access , configure () to access the mapping file (HBM.xml) of our defined Java objects and relational database tables, for example:

This configure () method creates a Configuration instance using various resources. For the entire project, if this Configuration instance is stored with a local thread, the entire project only needs to instantiate the Configuration object (Note: The Configuration instance takes time), which improves the efficiency of the project. Second, Hibernate Access Multiple Database Configuration

According to the above, the configure () method defaults to load us by accessing the Hibernate.cfg.xml element. HBM.xml file. We can also specify the HBM.xml file directly, for example, the addClass () method can load the corresponding mapping file directly by specifying the class, Hibernate will automatically convert the full name of the supplied Class to the file path, and you can use AddFile Method directly specifies the mapping file. For example: configuration configurate = new configuration (). Addclass ("book.class"); configuration configure = new configuration (). AddURL ("/book.class.getresource);

Configuration config = new configuration (). Addfile ("/ cat.hbm.xml);

This way, if multiple databases are configured with an XML configuration, then write multiple profiles. Here, assume that the corresponding two databases (one is mysql, one is SQLServer), we can define its XML file as "mysql.cfg.xml" and "sqlserver.cfg.xml". Configuration SessionFactory is acquired by the class code as follows: SessionFactory mysqlFactory = new Configuration () configure ( "/ mysql.cfg.xml") buildSessionFactory (); SessionFactory sqlserverFactory = new Configuration () configure ( "sqlserver.cfg.xml... ") .BUILDSESSIONFACTORY ();

If you use spring, multi-database is more simple, like this code can complete all configurations: org.gjt.mm.mysql.driver < / proty> root 123 Org.hibernate.diaalect.mysqldiaalect JDBC: ODBC: Test Sun.jdbc.odbc.jdbcodbcdriver < Value> 123 <

/ Bean> org.hibernate.dialect.SQLServerDialect test .hbm.xml ....... The above is just the general method of configuring Hibernate to access multiple databases, and Hibernate has many feasible configurations. Interested readers can refer to its Reference. About the Author:

Yang Xiao, Master of Computer, served as Java development in NEC and SoftBrain.

Blog: http://blog.sina.com.cn/u/1237288325