Configuring database connection pooling in Applicationcontext.xml

What is meant by using ${} in the applicationcontext.xml.

In the Applicationcontext.xml file, use ${xxx} to indicate that a variable is called "xxx" inside {XXX}.   For example: Configure the data connection pool in the Applicationcontext.xml file <!--Configure Data Link pool--<property name= "DataSource" > <bean  class= "Com.mchange.v2.c3p0.ComboPooledDataSource" > <property name= "Jdbcurl"  value= "${ Jdbcurl} "></property> <property name=" Driverclass " value=" ${driverclass} "></ property> <property name= "user"  value= "${user}" ></property> <property name= " Password " value=" ${password} "></property> <!--other Configurations-<!--get three connections when initializing, The value should be between Minpoolsize and Maxpoolsize. Default:3--<property name= "Initialpoolsize"  value= "3" ></property> <!--the minimum number of connections left in the connection pool. Default:3--<property name= "Minpoolsize"  value= "3" ></property> <!--the maximum number of connections left in the connection pool. Default:15--<property name= "maxpoolsize"  value= "></property> <!-- When the connection in the connection pool runs out, c3p0 the number of connections that are fetched at one time. Default:3--&GT <property name= "Acquireincrement"  value= "3" ></property> <!-- Controls the number of PreparedStatement loaded in the data source. If both maxstatements and maxstatementsperconnection are 0, the cache is closed. default:0--<property name= "maxstatements"  value= "8" ></property> <!-- Maxstatementsperconnection defines the maximum number of cache statements that a single connection in a connection pool has. default:0--<property name= "Maxstatementsperconnection"  value= "5" ></property> <!-- Maximum idle time, unused in 1800 seconds, the connection is discarded. If 0, it will never be discarded. default:0--<property name= "MaxIdleTime"  value= "1800" ></property> </bean> </ The part that is identified in the property> code is the function that uses the ${}. It is equivalent to calling a variable name in Java. In this example, these variables come from a different properties file. The properties are: jdbc.properties (primarily used to store some of the configuration of the JDBC Connection database for the next change without needing to be modified in the Applicationcontext.xml file.) ) Jdbc.properties:jdbcurl=jdbc:mysql://localhost:3306/oa driverclass=com.mysql.jdbc.driver user=root password= ${ The Jdbcurl in Jdbcurl} refers to the Jdbcurl in Jdbc.properties.