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Is it possible to add a URL pattern to a Servlet dynamically at runtime? For example, when the Servlet starts up, scan a folder for annotations, and then inject those url patterns into the servlet?

  • to provide more clarity -

In the Servlet's init file, I want to do this (pseudo-code)

// scan all the files in the package my.project.services
// find all the classes with the Annotation @Service
// read those annotations, find the url patterns in them, and insert them into the servlet
bluedevil2k
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  • Maybe I misunderstand. Do you want this at startup or later on? – Sotirios Delimanolis Jan 30 '14 at 16:19
  • At startup is OK. In the servlet's init() function for example. – bluedevil2k Jan 30 '14 at 16:22
  • What's the purpose? Are you sure this wouldn't be better-served by using a simple controller pattern? – Dave Newton Jan 30 '14 at 16:23
  • Maybe, but I'm trying to write a simple library for this project that will let me simply write new controllers, name their url patterns, and not edit the servlet or web.xml – bluedevil2k Jan 30 '14 at 16:26
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    Maybe you should use an existing library (spring-mvc or jersey for example)? –  Jan 30 '14 at 16:28
  • 1,2.Choose solution here http://stackoverflow.com/questions/259140/scanning-java-annotations-at-runtime. 3. Using generics get all fields by type of String, check on URL pattern. Do it in init of Servlet - profit! :) – lummycoder Jan 30 '14 at 16:31

1 Answers1

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I'm not sure I understand your end goal, but here's a possible solution.

With Servlet 3.0, implement the ServletContainerInitializer interface. Register it as the javadoc says

Implementations of this interface must be declared by a JAR file resource located inside the META-INF/services directory and named for the fully qualified class name of this interface

In its onStartup(..) method, you will have access to all the classes on your web application's classpath.

Scan them one by one. If a class is in the package you want and it has the annotation you are looking for, process it and store the URL pattern in a collection.

When the scan is done, you can register Servlet instances/classes with the provided ServletContext and register URL patterns with the given ServletRegistration.Dynamic object.

ServletRegistration.Dynamic registration = servletContext.addServlet("myServlet", new MyServlet());
registration.addMapping(yourCollectionAsAStringArray);

You have many other configuration options as well if you need them.

Sotirios Delimanolis
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