n0rm1e n0rm1e - 1 year ago 48
Java Question

How to provide a context configuration for a web application in Tomcat?

I have a web application that relies on some resources and parameters to be configured after it is installed, like a JDBC connection.

What I have come up with is providing a

which is copied into
by Tomcat when I deploy the application. This way all I am providing is a war file that can be copied into the appBase folder (webapps).
Tomcat's documentation says if there is such a file it won't be overwritten which is really great, since the changes made after deployment won't be lost.

But there is a subtle issue here:
Since we deploy the application by copying into webapps directory, Tomcat will first uninstall the existing application as well as the configuration file. This way the configuration file will be lost / overwritten which is not desirable.
Tomcat won't modify this behaviour as far as I know.

The question is:
Is there a way to work around this issue by installing the application in a way that Tomcat won't remove the existing configuration file.
Or, is there a better way of packaging the application?

Please note that we don't want to set autoDeploy to false and we cannot use human intervention for the installation (which rules out using Tomcat Manager web application).

If I get the configuration file out of .war file and copy it separately as
, Tomcat will still associate it with my application and remove it once I copy a new .war file.

Another assumption is: We don't know in advance the values to the configuration. We will only provide a sample configuration (a placeholder, if you wish) while actual configuration will be performed at some time later (not necessarily in the installation time).



I managed to resolve this issue somehow.

1- Install an exploded WAR directory somewhere outside Tomcat's appBase, let's assume it is in /usr/local/MyApp. [You can use a WAR file for this step instead of WAR directory, if your application runs from an unexploded war.]

2- Copy the context configuration file into [tomcat.conf]/[engine]/[hostname] directory, let's call it MyApp.xml. This file will point to the location of the application:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Context configuration file for my web application -->
<Context docBase="/usr/local/MyApp" privileged="true" antiResourceLocking="false" antiJARLocking="false">
        <Resource name="jdbc/myapp-ds" auth="Container" type="javax.sql.DataSource"
                maxActive="100" maxIdle="30" maxWait="10000" username="XXX" password="XXX"
                driverClassName="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost:3306/mydb" />

3- You are now free to go and modify the configuration file.

4- Update the application by copying new version of your application in /usr/local/MyApp


a) This solution applies to an unexpanded .war file as well, but since we use Spring's Log4JConfigListener it wouldn't run from an unexploded .war file. Tomcat doesn't explode .war files put outside appBase (webapps) folder.

b) This approach doesn't prevent you from having context.xml in /usr/local/MyApp/META-INF/context.xml since it will not be used by Tomcat in this configuration. You can use it in your dev environment, where you dump your .war file into the appBase (webapps) folder.

This is what I've got so far, still looking out for better solutions.