JShotgun

JShotgun (view source) is an auto reloading Java servlet. It can be used as a simple alternative to the complex reloading logic that is provided by some web frameworks.

JShotgun loads your application in a temporary class loader. It then watches any classes loaded from local files. If a class file is changed on disk it reloads the entire application. Classes loaded from jar files are excluded so only application code is reloaded. This also means that JShotgun automatically becomes a noop in most production environments.

You will need a method of automating the compilation. That could be anything from Eclipses Project Menu -> Build Automatically option to a simple shell script:

while true; do inotifywait *.java; javac *.java; done

Requires Java 7 and is fastest on operating systems with native WatchService support (Linux and Solaris). Reloads immediately in the background so most of the time theres no noticeable delay at all.

Concurrency safe: waits for any outstanding requests to be completed before reloading.

<servlet>
  <servlet-name>ExampleServlet</servlet-name>
  <servlet-class>org.meshy.jshotgun.ShotgunServlet</servlet-class>
  <init-param>
    <param-name>org.meshy.jshotgun.target</param-name>
    <param-value>org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher</param-value>
  </init-param>
</servlet>
<servlet-mapping>
  <servlet-name>ExampleServlet</servlet-name>
  <url-pattern>/*</url-pattern>
</servlet-mapping>

<repository>
 <id>clojars.org</id>
 <url>http://clojars.org/repo</url>
</repository>

<dependency>
  <groupId>org.meshy</groupId>
  <artifactId>jshotgun</artifactId>
  <version>1.0.0</version>
</dependency>