Prevent (tomcat) web application from starting if configuration incomplete

Question

How do I set a "configuration check" on a web application startup (Tomcat or other) and if the condition is not met the application should not start.

Let's say the application require a the file /tmp/dummy to exist on the fs in order to start. So I have something like

public class TestConfig {

    public static void TestServerConfiguration()  {
        if (! new File("/tmp/dummy").exists()) {
            // don't start this web application ... 
        }
    }

}

Where should I include this test?

Thanks!

Answer 1

I would go with a ServletContextListner . As with the servlet answer, it will not stop Tomcat but it will prevent the web application from loading. One advantage over the servlet answer is from the Javadoc:

All ServletContextListeners are notified of context initialization before any filters or servlets in the web application are initialized.

As an example:

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener; 

@WebListener
public class FileVerifierContextListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        // verify that the file exists.  if not, throw a RuntimeException
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
    }
}

Above assumes that your web.xml specifies a Servlet 3.0 or above environment (or that you don't have a web.xml at all):

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">
</web-app>

If you're using a lower servlet spec then you'll want to remove the @WebListener annotation and declare the listener in web.xml :

<web-app ...>
   <listener>
    <listener-class>
             com.example.package.name.FileVerifierContextListener 
        </listener-class>
   </listener>
</web-app>

Answer 2

One idea (but there can be others) is to implement a servlet that will do this check and exit when the condition is false. You need to run it at the beginning of the context deployment with the adequate load-on-startup tag. The web.xml will then look like :

<servlet>
  <display-name>startup condition servlet</display-name>
  <servlet-name>startup condition</servlet-name>
  <servlet-class>com.xxx.yyy.ConditionChecker</servlet-class>
  <load-on-startup>1</load-on-startup>
  <init-param>
    <param-name>FILE_TO_CHECK</param-name>
    <param-value>/tmp/dummy</param-value>
  </init-param>
</servlet>

This servlet could execute System.exit(1) when the condition is not met (/tmp/dummy doesn't exist). Please not this will kill the Tomcat. Not exactly stop the deployment process. If anyone want to fine tune this, you can edit my post.