Faster Web Application Deployment

The auto discovery features of the Servlet Specification can make deployments slow and uncertain. Auto discovery of web application configuration can be useful during the development as it allows new features and frameworks to be enabled simply by dropping in a jar file. However for production deployment, the need to scan the contents of many jars can have a significant impact at startup time.

The quickstart module allows a webapp to be pre-scanned, making startup predictable and faster. During scanning all declarative configuration (ie from web.xml, web-fragment.xml and annotations) are encoded into an effective web.xml, called WEB-INF/quickstart-web.xml, which can be inspected to understand what will be deployed.

Programmatic configuration is not encoded into the generated quickstart-web.xml file.

With quickstart, webapps that took many seconds to scan and deploy can now be deployed in a few hundred milliseconds.

Enabling

Enable the quickstart module for your jetty base:

$ cd $JETTY-BASE
$ java -jar $JETTY_HOME/start.jar --add-modules=quickstart

The $JETTY-BASE/start.d/quickstart.ini file contains these configurable parameters:

jetty.quickstart.mode

The values are:

AUTO

Allows jetty to run either with or without a quickstart-web.xml file. If jetty detects the file, then it will be used, otherwise the app is started normally.

GENERATE

In this mode, jetty will generate a quickstart-web.xml file and then terminate. Use this mode first before changing to either AUTO or QUICKSTART.

QUICKSTART

In this mode, if jetty does not detect a quickstart-web.xml file then jetty will not start.

jetty.quickstart.origin

Use this parameter to set the name of the attribute in the quickstart-web.xml file that contains the origin of each element. Knowing the descriptor or annotation from which each element derives can be useful for debugging. Note that the origin attribute does not conform to the web xml schema, so if you deploy with xml validation, you’ll see errors. It is probably best to do a few trial runs with the attribute set, then turn it off for final generation.

jetty.quickstart.xml

Use this parameter to change the name of the generated file. By default this is quickstart-web.xml in the webapp’s WEB-INF directory. The file named by this parameter will always be interpreted relative to WEB-INF.

If your webapp is a war file, you will need to either first unpack it yourself, or use a context xml file (or code equivalent) that calls WebAppContext.setExtractWAR(true). If you allow Jetty to do the unpacking, it will use the usual mechanisms to find the location to which to unpack. Note that by default Jetty unpacks to a temporary location which is not reused between executions. So either specify the directory to which to unpack, or make a work directory in your base to ensure the unpacked war is preserved and reused across restarts.