How spring references the configuration in the properties file

1.PropertyPlaceholderConfigurer class
It replaces the defined variable (var) in the attribute with a placeholder for ${var} in the spring's configuration file
< beans >
< Bean id = "Configbean" class = "Org.springframework.beans.factory.config.PropertyPlaceholderConfigurer" >
< name = "Location" > < value > db.properties </value > </property >
</Bean >
< Bean id = "DataSource" class = "Org.apache.commons.dbcp.BasicDataSource" Destroy-method = "Close" >
< property name = ' Driverclassname ' >< value > ${jdbc.driverclassname} </value ></property >
< property name = ' URL ' >< value > ${jdbc.url} </value ></property >
< property name = ' username ' >< value > ${jdbc.username} </value ></property >
< property name = ' password ' >< value > ${jdbc.password} </value ></property >
</Bean >
</Beans > Db.properties files
Jdbc.driverclassname=org.hsqldb.jdbcdriver
jdbc.url=jdbc:hsqldb:hsql://production:9002
Jdbc.username=sa
Jdbc.password=root 2.PropertyOverrideConfigurer Class
Same as Propertyplaceholderconfigurer function, but the usage is different. Do not use placeholders, in the properties file
Directly define the value of the property, which allows for a default value
< beans >
< Bean id = "Configbean" class = "Org.springframework.beans.factory.config.PropertyOverrideConfigurer" >
< property name = ' Location ' >< value > Db.properties </value ></Property >
</Bean >
< Bean id = "DataSource" class = "Org.apache.commons.dbcp.BasicDataSource" Destroy-method = "Close" >
< property name = ' Driverclassname ' >< value > Org.hsqldb.jdbcDriver </value ></Property >
< property name = ' URL ' >< value > jdbc:hsqldb:hsql://production:9002 </value ></Property >
< property name = ' username ' >< value >test </value ></Property >
< property name = ' Password ' >< value >123456 </value ></Property >
</Bean >
</Beans > Db.properties files
Datasource.username=admin
datasource.password=9527 when the bean instance is in place, admin,9527 replaces the test,123456
3 other
1 If you need to refer to multiple properties, change the Configbean property to
< property name = "Locations" >
< list >
< value > db.properties </value >
< value > db1.properties </value >
</list >
</Property > 2) automatically invokes the Beanfactorypostprocessor interface in Applactioncontext and must be manually added if it is to be used in Beanfactory:
Xmlbeanfactory factory = new Xmlbeanfactory (New Filesystemresource ("Beans.xml"));
Propertyplaceholderconfigurer cfg = new Propertyplaceholderconfigurer ();
Cfg.setlocation (New Filesystemresource ("Jdbc.properties"));
Cfg.postprocessbeanfactory (Factory);