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To understand Jetty configuration, you need to understand the "How" and the "What". This section covers how to configure Jetty in terms of what mechanisms exist to perform configuration. The next section gives an overview of the action components and fields that you can configure with these mechanisms.
The core components of Jetty are simply Plain Old Java Objects (POJOs); the process of configuring Jetty is mostly the process of instantiating, assembling and setting fields on the Jetty POJOs. You can achieve this either by:
Writing Java code to directly instantiate and assemble Jetty objects. This is referred to as Embedding Jetty.
Using Jetty XML configuration, which is an Inversion
of Control (IoC) framework, to instantiate and assemble Jetty
objects as XML objects. The
etc/jetty.xml file is
the main Jetty XML configuration file, but there are many other
files included in the jetty distribution.
Because the main Jetty configuration is done by IoC, the Jetty API documentation is the ultimate configuration reference.
The Jetty distribution uses the following configuration files to instantiate, inject and start server via the start.jar mechanism
The Jetty Start mechanism uses the command line, the start.ini file and any start.d/*.ini files to create an effective command line of arguments. Arguments may be:
XML files in Jetty IoC (or spring) XML format
Module activations in the form --module=name
Property in the form of name=value, used to parameterize Jetty IoC XML
A standard Java property file containing additional start properties
Other start.jar options (see java -jar start.jar --help)
Some JVM options
Ini files are located in the jetty.base (if different from jetty.home) and are typically edited to change the configuration.
The modules/*.mod files contain the definition of modules that can be activated by --module=name. Each mod file defines:
Module dependencies for ordering and activation
The libraries needed by the module to be added to the classpath
The XML files needed by the module to be added to the effective command line
Files needed by the activated module
A template ini file to be used when activating with the --add-to-start=name option
Mod files are normally located in jetty.home, but may be overridden in jetty.base if need be. Typically module files are rarely edited and only for significant structural changes.
XML files in Jetty or spring IoC format are listed either on the command line, ini files or added to the effective command line by a module definition. The XML files instantiate and inject the actual Java objects that comprise the server, connectors and contexts. Because Jetty IoC XML files frequently use properties, many common configuration tasks can be accomplished without editing these XML files. If XML configuration changes are required, the XML file should be copied from jetty.home/etc to jetty.base/etc before being modified.
In addition to the start configuration files described above, the configuration of the server can use the following file:
Any XML files in Jetty or spring IoC format that is discovered in the webapps directory are used by the deploy module to instantiate and inject HttpContext instances to create a specific context. These may be standard web applications or bespoke contexts created from special purpose handlers.
Specification defines the
web.xml deployment descriptor that
defines and configures the filters, servlets and resources a web
application uses. The Jetty WebAppContext component uses this
XML format to:
Set up the default configuration of a web application context.
Interpret the application-specific configuration supplied
with a web application in the
Interpret descriptor fragments included in the
META-INF directory of Jar files within
Normally the web.xml file for a web application is found in the WEB-INF/web.xml location within the war file/directory or as web.xml fragments with jar files found in WEB-INF/lib. Jetty also supports multiple web.xml files so that a default descriptor may be applied before WEB-INF/web.xml (typically set to etc/webdefault.xml by the deploy module) and an override descriptor may be applied after WEB-INF/web.xml (typically set by a context XML file see test.xml)
Standard Java property files are also used for Jetty configuration in several ways:
To parameterize Jetty IoC XML via the use of the Property element.
To configure the default logging mechanism (StdErrLog). You can also plug in other logging frameworks, and also use property files (for example, log4j).
As a simple database for login usernames and credentials.
To understand the Jetty IoC XML format, consider the following example of an embedded Jetty server instantiated and configured in java:
Jetty IoC XML allows you to instantiate and configure the exact same server in XML without writing any java code:
In practise, most commonly used Jetty features have XML files that
are included in the standard distribution in the
directory. Thus configuring Jetty is often a matter of just editing
existing XML files and altering the configuration values within
With a normal distribution of Jetty, the configuration mechanisms introduced above are typically used as follows:
Used for global command line options. In the standard Jetty
distribution since release 9.1 the contents of start.ini have been
moved to modular ini files under the
A directory of modular ini files that are used to set the OPTION, parameters and configuration files for key Jetty modules. These modules may be enabled/disabled by renaming the files or since release 9.1 by using the --enable or --disable option of start.jar
Jetty IoC XML files that configure individual features; for
jetty.xml (for the server),
The directory in which standard WAR files, web applications and context IoC XML files are deployed.
The following example examines the common Jetty configuration mechanism using the HTTP port as an example. To run the Jetty server from the distribution, it is just a matter of running the following command:
> java -jar start.jar
distribution uses the start.d/
directory to define what modules, configuration files and
properties are defined. The start.d/http.ini module is enabled by default
and contains the following lines (among others):
This sets the Jetty port parameter and activates the http module as
defined by the modules/http.mod file, which lists the
etc/jetty-http.xml configuration file as an effective
command line argument. Looking inside that configuration file, we see that
it calls addConnector on the server with a new instance of the
ServerConnector class. This instance is configured in XML and includes the
The effect of this line is to call ServerConnector.setPort(int) with
either the value of the
jetty.port property if set or
with the value 80. We can see from the start.ini except above that the
jetty.port property line is set to 8080, so out of the box, the Jetty
distribution will use the default 8080 port set inside the
If you wish to change the port, then the start.d/http.ini file can be edited and the default value there changed to the new port. However this does mean that a file which is part of the Jetty distribution has been modified, which can make future upgrades more difficult. Thus it is normally better to create a jetty.base directory and configure a new instance of a server there.