Chapter 3. Jetty Configuration Introduction

Chapter 3. Jetty Configuration Introduction
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Table of Contents

How to Configure Jetty
What to Configure in Jetty

How to Configure Jetty

Jetty POJO Configuration
Jetty Start Configuration Files
Other Configuration Files
Jetty IoC XML format

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.

Jetty POJO Configuration

The core components of Jetty are Plain Old Java Objects (POJOs); the process of configuring Jetty is mostly the process of instantiating, assembling and setting fields on the Jetty POJOs. This can be achieved 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 etc/jetty-__feature__.xml files included in the Jetty distribution.
Using a third party IoC framework like Spring, to instantiate and assemble Jetty objects as Spring beans.

Because the main Jetty configuration is done by IoC, the Jetty API documentation is the ultimate configuration reference.

Jetty Start Configuration Files

The Jetty distribution uses the following configuration files to instantiate, inject and start server via the start.jar mechanism.

ini files

The Jetty Start mechanism uses the command line, the $JETTY_BASE/start.ini and/or $JETTY_BASE/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 in combination with --exec, such as -Xbootclasspath.
As of Jetty 9 it is the ini files located in the Jetty base directory (if different from Jetty home) that are typically edited to change the configuration (e.g. change ports).

mod files

The $JETTY_HOME/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 the --add-to-start=name option
Typically module files are rarely edited and only then for significant structural changes. The *.mod files are normally located in $JETTY_HOME/modules/, but extra or edited modules may be added to $JETTY_BASE/module. If module changes are required, it is best practice to copy the particular *.mod file from $JETTY_HOME/modules/ to $JETTY_BASE/modules/ before being modified.

XML files

XML files in Jetty IoC XML format or Spring IoC format are listed either on the command line, in ini files, or are 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 use properties, most common configuration tasks can be accomplished without editing these XML files and can instead be achieved by editing the property in the corresponding ini files. XML files are normally located in $JETTY_HOME/etc/, but extra or edited XML files may be added to $JETTY_BASE/etc/. If XML configuration changes are required, it is best practice to copy the XML file from $JETTY_HOME/etc/ to $JETTY_BASE/etc/ before being modified.

Below is an illustration of how the various Jetty configuration files (ini, mod and XML) are related:

Other Configuration Files

In addition to the configuration files described above, the configuration of the server can use the following file types:

Context XML files

Any XML files in Jetty IoC XML format 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.

web.xml

The Servlet 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 WEB-INF/web.xml file.
Interpret descriptor fragments included in the META-INF directory of Jar files within WEB-INF/lib.
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)

Property Files

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). Other logging frameworks can be utilized and also use property files (for example, log4j).
As a simple database for login usernames and credentials.

Jetty IoC XML format

To understand the Jetty IoC XML format, consider the following example of an embedded Jetty server instantiated and configured in Java:

//
//  ========================================================================
//  Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.embedded;

import org.eclipse.jetty.server.Connector;
import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.ServerConnector;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.handler.HandlerCollection;
import org.eclipse.jetty.servlet.ServletContextHandler;

public class ExampleServer
{
    public static void main( String[] args ) throws Exception
    {
        Server server = new Server();

        ServerConnector connector = new ServerConnector(server);
        connector.setPort(8080);
        server.setConnectors(new Connector[] { connector });

        ServletContextHandler context = new ServletContextHandler();
        context.setContextPath("/");
        context.addServlet(HelloServlet.class, "/hello");
        context.addServlet(AsyncEchoServlet.class, "/echo/*");

        HandlerCollection handlers = new HandlerCollection();
        handlers.setHandlers(new Handler[] { context, new DefaultHandler() });
        server.setHandler(handlers);

        server.start();
        server.join();
    }
}

Jetty IoC XML format allows you to instantiate and configure the exact same server in XML without writing any java code:

<?xml version="1.0"?>
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure_9_3.dtd">

<Configure id="ExampleServer" class="org.eclipse.jetty.server.Server">

  <Set name="connectors">
    <Array type="org.eclipse.jetty.server.Connector">
      <Item>
        <New class="org.eclipse.jetty.server.ServerConnector">
          <Arg><Ref refid="ExampleServer"/></Arg>
          <Set name="port">8080</Set>
        </New>
      </Item>
    </Array>
  </Set>

  <New id="context" class="org.eclipse.jetty.servlet.ServletContextHandler">
    <Set name="contextPath">/hello</Set>
    <Call name="addServlet">
      <Arg>org.eclipse.jetty.embedded.HelloServlet</Arg>
      <Arg>/</Arg>
    </Call>
  </New>

  <Set name="handler">
    <New class="org.eclipse.jetty.server.handler.HandlerCollection">
      <Set name="handlers">
        <Array type="org.eclipse.jetty.server.Handler">
          <Item>
            <Ref refid="context" />
          </Item>
          <Item>
            <New class="org.eclipse.jetty.server.handler.DefaultHandler" />
          </Item>
        </Array>
      </Set>
    </New>
  </Set>
</Configure>

In practice, most commonly used Jetty features have XML files that are included in the standard distribution in the etc directory. Thus configuring Jetty is often a matter of just editing existing XML files and altering the property values injected into them.

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