On JEE 6 webapps startup time 25 Mar 2012

While working on Tomcat 7 embedded to automate my integration tests, I realized that my integration tests wasted much of the time in starting/stopping the server. Even if I do not start the integration tests as often as the unit tests, it becomes rapidly irritating. Furthermore, during development I tend to restart the server a couple of times per hour, especially at the beginning of the project. Sure hot deployment helps, but it is not always enough.

On my Mac Book Pro, a cold start took around 10s. Interestingly enough, an empty Tomcat startups in less than a second. The problem comes from the fact that Tomcat 7 scans the classpath to find out annotations that declare Servlets using the @WebServlet. This, even if you do not use that feature. Don’t get me wrong, not having to configure XML is cool but I am not ready to pay such a high price for it. Especially as the only servlet I use, is the JSF one.

Where do we start from?

For these tests, I use a JEE6 application with JSF, Weld and JPA (no EJBs) that runs under Tomcat.
This is a demo application called JEE-6-Demo that I use to teach JEE6. A mentioned previously, a cold start (without tuning anything) requires around 10s on my Mac Book Pro Intel Core i7 with 8Gb RAM : INFO: Server startup in 9992 ms

Step 1: Avoid looking for @WebSerlet and co.

By default, Tomcat 7 (along with the Servlet 3.0 specification) scans the classpath to look for classes that are annotated @WebServlet,@WebServletContextListener, @ServletFilter, or @InitParamJSF. It is a nice feature as you do not have to specify the faces servlet anymore. However, it comes at a price: depending of the classpath this can be very long. To solve this issues, simple add the metadata-complete="true" to the web-app element of our WEB-INF/web-xml attribute to avoid scanning the classpath.

<web-app metadata-complete="true"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	id="MyWebApp" version="3.0">

Obviously, as it is no more automatically discovered, we have to manually add the faces servlet to the context:

		<servlet-name>Faces Servlet</servlet-name>

		<servlet-name>Faces Servlet</servlet-name>

Using these modifications in web.xml, the startup time came down to around 4.5 seconds: INFO: Server startup in 4404 ms

Step 2: Avoid looking for @ManagedBean and co.

Similarly, the is a similar feature in JSF 2.0. By default, the JSF implementation looks for classes annotated with As I use Weld and its @Named, @SessionScoped, and so on, I can disable this feature in JSF.

<faces-config xmlns="http://java.sun.com/xml/ns/javaee"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_2_0.xsd"
   version="2.0"  metadata-complete="true">

Using this modification in faces-config.xml, the startup time came down to around 3.7 seconds: INFO: Server startup in 3730 ms

Step 3: Limiting Weld’s scanning

Finally, I would like to keep Weld scanning to discover the @Named, @Inject, and other Weld annotations but I would like to limit it to my a subset of the classes of the jar. To that end simply add weld:scan directive and include a pattern with packages to scan.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://java.sun.com/xml/ns/javaee" 
           http://java.sun.com/xml/ns/javaee http://jboss.org/schema/cdi/beans_1_0.xsd
           http://jboss.org/schema/weld/beans http://jboss.org/schema/weld/beans_1_1.xsd">
    <weld:include pattern="ch.demo.*"/>

Using this modification in beans.xml, the startup time came down to around 3.3 seconds: INFO: Server startup in 3312 ms

To conclude, using these minor modifications I divided the startup time by three. This is very useful during development and integration tests when the server is started and stopped many times.