Question

MyBatis documentation shows a way to build a SqlSessionFactory through XML configuration file or a Configuration object through Java code. It also mentions passing properties that will override what is specified in the XML file.

I am trying use the properties facility to supply a data source URL in addition to the XML configuration, but the property does not get set.

Here’s the configuration XML I am using (removed all the aliases and mappings for brevity):

<configuration> 
  <typeAliases>
    <typeAlias alias="Item" type="com.example.project.Item"/> 
  </typeAliases>

  <environments default="development"> 
      <environment id="development"> 
      <transactionManager type="JDBC"/> 
      <dataSource type="POOLED"> 
        <property name="driver" value="org.h2.Driver"/> 
        <property name="url" value="jdbc:h2:C:/path_to_db_file_in_the_filesystem"/>   
        <property name="username" value="sa"/> 
        <property name="password" value="sa"/>     
      </dataSource> 
    </environment> 
  </environments> 

  <mappers> 
    <mapper resource="com/example/project/mappers/ItemMapper.xml"/> 
  </mappers>

</configuration> 

The XML file works fine for everything, but I need to supply the url through Java code (through the code, it is obtained from another configuration file so it has to be dynamically supplied to MyBatis). I know I can do it all in code, but that will be unnecessary work so I would like to avoid that route if possible.

Based on the description in the manual, I removed the url line from the XML file and came up with the following code:

String resource = "com/example/project/MyBatisConfiguration.xml"; 
Reader reader = Resources.getResourceAsReader(resource); 

Properties props = new Properties();
props.setProperty("url", url);
SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(reader, props);

The code builds the SqlSessionFactory, but I get the “url cannot be null” exception, indicating that the property was not successfully overwritten. I think the name of the property should be in a special format, but I could not find out what that format is.

Thanks a lot in advance for all the help.

Answer 1

In your configuration XML you can insert a placeholder for the datasource URL like that:

<property name="url" value="${url}"/>

Then the build() method of SqlSessionFactoryBuilder replaces "${url}" in the XML with the value of property "url" provided by props.