Structure of the JNLP File

This topic describes the syntax of the Java Network Launch Protocol (JNLP) file for rich Internet applications (RIAs).

The following code snippet shows a sample JNLP file for a Java Web Start application: 

<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+" codebase="" href="">
 <information>
 <title>Dynamic Tree Demo</title>
 <vendor>Dynamic Team</vendor>
 <icon href="sometree-icon.jpg"/>
 <offline-allowed/>
 </information>
 <resources>
 <!-- Application Resources -->
 <j2se version="1.6+" href=
 "http://java.sun.com/products/autodl/j2se"/>
 <jar href="dynamictreedemo.jar"
 main="true" />
 </resources>
 <application-desc
 name="dynamic tree demo application"
 main-class="webstartComponentArch.DynamicTreeApplication" >
 </application-desc>
 <update check="background"/>
</jnlp>

The following table describes the elements and attributes commonly used in JNLP files. Click the parent link to view an element's parent.

Note: This table does not include all possible contents of the JNLP file. For more information, see the Java Network Launching Protocol and API Specification Change Log.
Commonly Used Elements and Attributes in a JNLP file

Element

Attributes

Description

Since

Required

jnlp

The topmost xml element for a JNLP file.

1.0

Yes

spec

Value of the attribute can be 1.0, 1.5, or 6.0, or can use wildcards such as 1.0+. It denotes the minimum version of the JNLP Specification that this JNLP file can work with.

1.0

codebase

The base location for all relative URLs specified in href attributes in the JNLP file.

1.0

href

The URL of the JNLP file itself.

1.0

version

The version of the RIA being launched, as well as the version of the JNLP file itself.

1.0

information

Contains other elements that describe the RIA and its source.

1.0

Yes

os

The operating system for which this information element should be considered.

1.5.0

arch

The architecture for which this information element should be considered.

1.5.0

platform

The platform for which this information element should be considered.

1.5.0

locale

The locale for which this information element should be considered.

1.5.0

title

The title of the RIA.

1.0

Yes

vendor

The provider of the RIA.

1.0

Yes

homepage

The homepage of the RIA.

1.0

href

A URL pointing to where more information about this RIA can be found.

1.0

Yes

description

A short statement describing the RIA.

1.0

kind

An indicator as to the type of description. Legal values are one-line, short, and tooltip.

1.0

icon

An icon that can be used to identify the RIA to the user.

1.0

href

A URL pointing to the icon file. Can be in one of the following formats: gif, jpg, png, ico.

1.0

Yes

kind

Indicates the suggested use of the icon, can be: default, selected, disabled, rollover, splash, or shortcut.

1.0

width

Can be used to indicate the resolution of the image.

1.0

height

Can be used to indicate the resolution of the image.

1.0

depth

Can be used to indicate the resolution of the image.

1.0

offline-allowed

Indicates that this RIA can operate when the client system is disconnected from the network.

1.0

shortcut

Can be used to indicate the RIA's preferences for desktop integration.

1.5.0

online

Can be used to describe the RIA's preference for creating a shortcut to run online or offline.

1.5.0

desktop

Can be used to indicate the RIA's preference for putting a shortcut on the user's desktop.

1.5.0

menu

Can be used to indicate the RIA's preference for putting a menu item in the user's start menus.

1.5.0

sub-menu

Can be used to indicate the RIA's preference for where to place the menu item.

1.5.0

association

Can be used to hint to the JNLP client that the RIA wants to be registered with the operating system as the primary handler of certain extensions and a certain mime-type. If this element is included, either the offline-allowed element must also be included, or the href attribute must be set for the jnlp element.

1.5.0

extensions

A list of file extensions (separated by spaces) that the RIA requests it be registered to handle.

1.5.0

mime-type

The mime-type that the RIA requests it be registered to handle.

1.5.0

related-content

An additional piece of related content that can be integrated with the RIA.

1.5.0

href

A URL pointing to the related content.

1.5.0

Yes

update

The preferences for how RIA updates should be handled by the JNLP client.

1.6.0

check

The preference for when the JNLP client should check for updates. Value can be always, timeout, or background..

1.6.0

policy

The preference for how the JNLP client should handle a RIA update when a new version is available before the RIA is launched. Values can be always, prompt-update, or prompt-run.

1.6.0

1.0

security

Can be used to request enhanced permissions. If this element is not included, the application is run in the security sandbox.

1.0

all-permissions

Requests that the RIA be run with all permissions.

1.0

j2ee-application-client-permissions

Requests that the RIA be run with a permission set that meets the security specifications of the J2EE application client environment.

1.0

resources

Describes all the resources that are needed for the RIA.

1.0

Yes

os

The operating system for which the resources element should be considered.

1.0

arch

The architecture for which the resources element should be considered.

1.0

locale

The locales for which the resources element should be considered.

java or j2se

Versions of Java software to run the RIA with.

1.6.0 (java)

version

Ordered list of version ranges to use.

1.0

Yes

href

The URL denoting the supplier of this version of Java software, and from where it can be downloaded.

1.0

java-vm-args

An additional set of standard and non-standard virtual machine arguments that the RIA would prefer the JNLP client use when launching the JRE software.

1.0

initial-heap-size

The initial size of the Java heap.

1.0

max-heap-size

The maximum size of the Java heap.

1.0

jar

A JAR file that is part of the RIA's classpath.

1.0

Yes

href

The URL of the JAR file.

1.0

Yes

version

The requested version of the JAR file. Requires using the version-based download protocol

1.0

main

Indicates if this JAR file contains the class containing the main method of the RIA.

1.0

download

Indicates that this JAR file can be downloaded lazily, or when needed.

1.0

size

The downloadable size of the JAR file in bytes.

1.0

part

Can be used to group resources together so that they are downloaded at the same time.

1.0

nativelib

A JAR file that contains native libraries in its root directory.

1.0

href

The URL of the JAR file.

1.0

Yes

version

The requested version of the JAR file. Requires using the version-based download protocol

1.0

download

Can be used to indicate this JAR file can be downloaded lazily.

1.0

size

The downloadable size of the JAR file in bytes.

1.0

part

Can be used to group resources together so they will be downloaded at the same time.

1.0

extension

A pointer to an additional component-desc or installer-desc to be used with this RIA.

1.0

href

The URL to the additional extension JNLP file.

1.0

Yes

version

The version of the additional extension JNLP file.

1.0

name

The name of the additional extension JNLP file

1.0

ext-download

Can be used in an extension element to denote the parts contained in a component-extension.

1.0

ext-part

The name of a part that can be expected to be found in the extension.

1.0

Yes

download

Can be used to indicate this extension can be downloaded eagerly or lazily.

1.0

part

Denotes the name of a part in this JNLP file in which to include the extension.

1.0

package

Can be used to indicate to the JNLP client which packages are implemented in which JAR files.

1.0

name

Package name contained in the JAR files of the given part.

1.0

Yes

part

Part name containing the JAR files that include the given package name.

1.0

Yes

recursive

Can be used to indicate that all package names, beginning with the given name, can be found in the given part.

1.0

property

Defines a system property that will be available through the System.getProperty and System.getProperties methods.

1.0

name

Name of the system property.

1.0

Yes

value

Value of the system property.

1.0

Yes

Note: A JNLP file must contain one of the following: application-desc, applet-desc, component-desc, or installer-desc.

1.0

Yes

application-desc

Denotes this is the JNLP file for an application.

1.0

main-class

The name of the class containing the public static void main(String[]) method of the application.

1.0

Yes

argument

Each argument contains (in order) an additional argument to be passed to the main method.

1.0

applet-desc

Denotes this is the JNLP file for an applet.

1.0

main-class

The name of the main applet class.

1.0

Yes

documentbase

The document base for the applet as a URL.

1.0

name

Name of the applet.

1.0

Yes

width

The width of the applet in pixels.

1.0

Yes

height

The height of the applet in pixels.

1.0

Yes

param

A set of parameters that can be passed to the applet.

1.0

name

The name of this parameter.

1.0

Yes

value

The value of this parameter.

1.0

Yes

component-desc

Denotes this is the JNLP file for a component extension.

1.0

installer-desc

Denotes this is the JNLP file for an installed extension.

1.0

main-class

The name of the class containing the public static void main(String[]) method of the installer.

1.0

Yes

Encoding JNLP Files

Java Web Start software supports encoding of JNLP files in any character encoding supported by the Java platform. For more information about character encoding in the Java platform, see the Supported Encodings Guide. To encode a JNLP file, specify an encoding in the XML prolog of that file. For example, the following line indicates that the JNLP file is encoded in UTF-16. 

<?xml version="1.0" encoding="utf-16"?>
Note: The XML prolog itself must be UTF-8-encoded.