Tomcat 8 URL Rewriting

This repository explores different setups for URL Rewrite Valve introduced in Tomcat 8. This should not be confused with Apache Web Server's mod_rewrite. They are both essentially the same but instead of having a Apache Web Server in front of a Tomcat for url rewriting, Tomcat can now do it on its own.

Why URL Rewriting

1. Context block in Tomcat does not support Regex
2. SPA application deployed in Tomcat needs to always be pointed to index.html inside webapps/spa-application, regardless of URL displayed in browser

Checklist

1. Tomcat 8
2. Rewrite Valve enabled (global or per app)
3. rewrite.config for url rewriting rules created (global or per app)

Basics

1. Rewrite Valve can be enabled on Tomcat globally by adding org.apache.catalina.valves.rewrite.RewriteValve to $catalina_home/conf/context.xml (This context.xml is automatically loaded for every application in the Tomcat)

   <Context>
       <Valve className="org.apache.catalina.valves.rewrite.RewriteValve"/>
   </Context>

2. It can also be enabled on a per-application basis by adding this Valve to the Context block in $catalina_home/conf/server.xml

         <Host appBase="webapps" autoDeploy="true" name="localhost" unpackWARs="true">
   
         <!-- Activating rewrite valve for AppOne only -->
         <Context docBase="H:\tools\apache-tomcat-8.5.3\webapps\applicationOne" path="/AppOne" reloadable="true" >
               <Valve className="org.apache.catalina.valves.rewrite.RewriteValve"/>
         </Context>
         <Context docBase="H:\tools\apache-tomcat-8.5.3\webapps\applicationTwo" path="/AppTwo" reloadable="true"/>
         </Host>

3. rewrite.config file will be read globally (on all contexts/applications) if it's created in $catalina_home/webapps/ROOT/WEB-INF or per-app if created in e.g. $catalina_home/webapps/applicationOne/WEB-INF.

   Note: If rewrite.config is created on app-level, it will only start url-matching after the application's context. e.g. http://localhost:8084/applicationOne/paths-after-this-will-be-matched. On global level, http://localhost:8084/anything-after-this-will-be-matched

Setup 1

Different entry urls pointing to 1 application

Approach:

• Global level rewrite.config (assuming this tomcat has only 1 application)
• rewrite.config location: $catalina_home/webapps/ROOT/WEB-INF

RewriteCond %{REQUEST_URI} /path/two/(.*) [OR]
RewriteCond %{REQUEST_URI} /path/one/(.*)
RewriteRule ^/(path\/(one||two))/(.*)  /applicationOne/$3

Explanation:

• Two different possible URLs are matched
• If any of them matches, the path that's in (.*) will replace $3 in RewriteRule
• e.g. http://localhost:8084/path/one/dashboard?query=11 will be rewritten as http://localhost:8084/applicationOne/dashboard?query=11

Alternatively, RewriteCond can be skipped with this rule, both behaves similarly

RewriteRule ^/path/two/(.*) /applicationOne/$1
RewriteRule ^/path/one/(.*) /applicationOne/$1

Setup 2

Different entry urls pointing to different applications

Approach

• Global level rewrite.config (necessary since it needs to be higher level than any application's context)
• rewrite.config location: $catalina_home/webapps/ROOT/WEB-INF

RewriteRule ^/path/one/ui/(.*)  /applicationTwo/$1
RewriteRule ^/path/one/(.*)  /applicationOne/$1
RewriteRule ^/path/two/(.*)  /applicationOne/$1

Explanation:

• Assumes backend application ($catalina_home/webapps/applicationOne) has multiple entry urls.
• Assumes ui application is an SPA deployed in the same Tomcat
• /path/one/ui has to be higher up in the rule order so that it does not get overridden by RewriteRule under it