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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
The Invoker

Who, what or where is the Invoker? There are web sites that have a lot of pages on them, none of which is served up all that often, and there are other web sites which only host a few web applications,each of which is run in a container service such as Catalina within Tomcat. In the first case, the web site developer / maintainer wants to simply add extra pages to the appropriate directory and have them appear at their own URLs, but in the latter case (s)he will usually want to specifically point individual URLs at individual applications. And on Tomcat, this is done though the web.xml file.

But just occasionally under Tomcat, there's a requirement to be able to copy a Class that contains a servlet on the web server, and have it available straight away - no mucking about with web.xml. For example, I'm training systems administrators who will be looking after a system used by Java classes (University ones, not ours!) this week, and their students need to be able to upload a class that contains a servlet, and with minimal fuss and editing, test it on the server. This is where the Invoker comes in.

To enable the invoker ... in the administrator's main web application configuration file (also called web.xml, but in the conf directory), remove the comments that disable the Invoker in the sample file supplied with the Tomcat distribution. That extra code comes in two sections - one to define what the invoker IS and and other to define how it MAPS - and you need them both. Then kick [restart] your Tomcat.

To use the invoker for a new Servlet ... place the class file in the WEB-INF/classes subdirectory of your web application, and visit it via a URL of the form:
where webappname is the name of your web application (directory name in the webapps folder) and Whichone is the class name - i.e. the file is called Whichone.class. The word "servlet" is 'hard coded' in the web.xml file - you can change it server-wide if you wish!

We go through all of this (and much, much more!) on our Deploying Apache httpd / Tomcat course. Illustration - a waiter at Gun Wharf in Portsmouth
(written 2009-02-13, updated 2009-02-15)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
A654 - Web Application Deployment - Configuring and Controlling Tomcat
  [837] Tomcat - Shutdown port - (2006-08-18)
  [907] Browser -> httpd -> Tomcat -> MySQL. Restarting. - (2006-10-28)
  [914] A practical example of roles - (2006-11-04)
  [1351] Compressing web pages sent out from server. Is it worth it? - (2007-09-14)
  [1370] Apache Tomcat Performance Tuning - (2007-09-29)
  [1503] Web page (http) error status 405 - (2008-01-12)
  [1553] Automatic startup and shutdown of Tomcat - (2008-02-24)
  [1762] WEB-INF (Tomcat) and .htaccess (httpd) - (2008-08-20)
  [1943] Port and Glasses - (2008-12-14)
  [1994] tomcat-users.xml; what a difference a space made - (2009-01-16)
  [2061] Tomcat 6 - Annotated Sample Configuration Files - (2009-03-01)
  [2163] CATALINA_OPTS v JAVA_OPTS - What is the difference? - (2009-05-09)
  [2652] Reading and writing cookies in Java Servlets and JSPs - (2010-02-26)
  [3043] Gathering information - logging - with log4j. First steps. - (2010-11-12)

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Some other Articles
Confidence, Customer Service and Tourism in Melksham
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httpd, Tomcat and PHP course enhancements
Error: Cant read xxxxx: no such variable (in Tcl Tk)
The Invoker
Sticky Sessions with mod_jk (httpd to Tomcat)
The Interview and The Lift
Java Tag Libraries / how they work / Tomcat Deployment
1234567890 ... coming up on Friday 13th
Through Snow and Flood to Linux and Tomcat
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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