Externalize of properties file in Tomcat

Below is the approach that can be used for externalize ApplicationResource properties file in Tomcat 7 & 9.

Steps:

1.       The change needs to be done in <tomcat_installation_path>/conf/Catalina/localhost/<APP_NAME>.xml (where data sources are defined)

2.       E.g. ApplicationResource.properties file is kept in D:/AppProperties/TestApp path

3.       For Tomcat 7.x , need to add the folder in classpath by using below tag under <Context> tag

a.       <Resources className="org.apache.naming.resources.VirtualDirContext"

               extraResourcePaths="/WEB-INF/classes=D:/AppProperties/TestApp"/>

4.       For Tomcat 8.x/9.x, you can provide the properties file instead of directory itself, by using below tag under <Context> tag

a.       <Resources>
    <PreResources className="org.apache.catalina.webresources.FileResourceSet"
            base="D:/AppProperties/TestApp/ApplicationResource.properties"
            webAppMount="/WEB-INF/classes/ApplicationResource.properties" />
     </Resources>
b. Alternatively, to configure directory the below one can be used

<Resources>
<PreResources className="org.apache.catalina.webresources.DirResourceSet"
base="D:/AppProperties/TestApp"
webAppMount="/WEB-INF/classes"/>

</Resources>

5.       This will load the properties file from the external location; hence remove the properties file from WEB-INF/classes