SpringMVC: PropertyPlaceHolder

Another interesting support feature provided by Spring is using properties in your code through PropertyPlaceholderConfigurer. It helps load application properties from either a file or database table. The XML for using both,which will go into your spring context file,is 

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">

    <property name="properties">

        <bean class="org.apache.commons.configuration.ConfigurationConverter"

             factory-method="getProperties">

                 <constructor-arg>

                   <bean class="org.apache.commons.configuration.DatabaseConfiguration">

                          <constructor-arg ref="<database bean>" />

                          <constructor-arg value="<database property table>" />

                          <constructor-arg value="<tablecolumn for placeholdernames>" />

                          <constructor-arg value="<tablecolumn for placeholdervalues>" />

                   </bean>

                </constructor-arg>

        </bean>

     </property>

     <property name="locations">

         <list>

            <value>file:src/main/webapp/WEB-INF/application.properties</value>

         </list>

     </property>

</bean>

<constructor-arg value="datasource" /> refers to a database bean defined in the spring context xml.

<constructor-arg value="app_config" /> refers to a database table APP_CONFIG.

<constructor-arg value="config_key" /> refers to column 'CONFIG_KEY' in APP_CONFIG that will contain the property you want to use in your code.

<constructor-arg value="config_value" />  refers to column 'CONFIG_VALUE' in APP_CONFIG that will contain the corresponding value of the property.

The below example shows how to then use the pre-loaded properties in your Spring code.

@Controller

public class DocumentController{

     @Value("${doc_Base}")

      String docBase="";

      @Value("${app_Env}")
      String appEnv=null;
      @Value("${doc_Path}")
      String docPath="";

      @Autowired
      private DocumentDAO documentDao;

      @Autowired
      private UserDAO userDao;

      @RequestMapping(value="/upload")
      public String uploadDocument(@RequestParam("docName)String documentName,
                                  @RequestParam("docFile")MultipartFile file)
      {
         <upload logic>

     }

       

}

The members docBase,appEnv & docPath will be initialized when the Controller instance gets created. Here doc_Base,app_Env & doc_Path are property names defined in CONFIG_KEY & their corresponding values in CONFIG_VALUE will be used for initialization

CONFIG_KEY       CONFIG_VALUE
doc_Base              test
app_Env               Dev
doc_Path              /dev/reviews



References

http://forum.spring.io/forum/spring-projects/container/82142-propertyplaceholderconfigurer-problems