This section describes the basics of deploying an application using Java Web Start. Deploying an application involves the following steps:

1. Setting up the Web Server
2. Creating the JNLP File
3. Placing the Application on the Web Server
4. Creating the Web Page

This section uses the Notepad example application to demonstrate Java Web Start technology. You can find all the source files for the Notepad application example in the \demo\plugin\jfc\Notepad directory within the JDK installation directory.

The key to running an application with Java Web Start is the Java Network Launching Protocol, or JNLP, file. The JNLP file is an XML file that contains elements and attributes that tell Java Web Start how to run the application.

An Example JNLP File

Following is the JNLP file for the Notepad demo:

<?xml version="1.0" encoding="utf-8"?>
<!-- JNLP File for Notepad -->

<jnlp spec="1.0+"
      codebase="http://java.sun.com/docs/books/tutorialJWS/deployment/webstart/ex5/" 
      href="Notepad.jnlp">
   <information>
      <title>Notepad Demo</title>
      <vendor>The Java(tm) Tutorial: Sun Microsystems, Inc.</vendor>
      <description>Notepad Demo</description>
      <homepage href="http://java.sun.com/docs/books/tutorial/deployment/webstart/running.html"/>
      <description kind="short">ClickMeApp uses 3 custom classes plus several
       standard ones</description>
      <offline-allowed/>
   </information>
   <resources>     
   	<jar href="Notepad.jar"/>   
	<j2se version="1.3+"
	      href="http://java.sun.com/products/autodl/j2se"/>
   </resources>
   <application-desc main-class="Notepad"/>
</jnlp>

If you click this link to the Notepad.jnlp file, you open and run the Notepad application.

JNLP File Contents

The following table describes the elements and attributes in the sample JNLP file.

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Note: This table does not include all possible contents of the JNLP file. For more information, see the Java Network Launching Protocol & API Specification (JSR-56).

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Elements and Attributes of a JNLP file

Element	Attributes	Description	Since	Required
jnlp		This is the main xml element for a jnlp file. Everything is contained within the jnlp element.	1.0	yes
	spec	The spec attribute can be 1.0, 1.5.0, or 1.6.0 or can use the wildcards such as 1.0+. It denoted the minimum version of the JNLP Specification that this jnlp file can work with.	1.0
	codebase	The codebase attribute specifies the base location for all relative URLs specified in href attributes in the JNLP file.	1.0
	href	The href specifies the URL of the JNLP file itself.	1.0
	version	The version of the application being launched, as well as the version of the JNLP file itself.	1.0
information		The information element contains other elements that describe the application and it's source.	1.0	yes
	os	Specifies the operating system for which this information element should be considered.	1.5.0
	arch	Specifies the architecture for which this information element should be considered	1.5.0
	platform	Specifies the platform for which this information element should be considered.	1.5.0
	locale	Specifies the locale for which this information element should be considered.	1.5.0
title		The title element specifies the title of the application.	1.0	yes
vendor		The vendor element specifies the provider of the application.	1.0	yes
homepage		The homepage of the application.	1.0
	href	A URL pointing to where more information on this application can be found.	1.0	yes
description		A short statement describing the application.	1.0
	kind	An indicator as to what type of description this is, legal values are one-line, short, and tooltip.	1.0
icon		Describes an icon that can be used to identify the application to the user.	1.0
	href	A URL pointing to the icon file, may 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 application can operate when the client system is disconnected from the network.	1.0
shortcut		The shortcut element can be used to indicate an application's preferences for desktop integration.	1.5.0
	online	Can be used to describe the application's preference for creating a shortcut to run online or offline.	1.5.0
desktop		Can be used to indicate an application's preference for putting a shortcut on the users desktop.	1.5.0
menu		Can be used to indicate an application's preference for putting a menu item in the users start menus.	1.5.0
	sub-menu	Can be used to indicate an application's preference for where to place the menu item.	1.5.0
association		Can be used to hint to the JNLP client that it wishes to be registered with the operating system as the primary handler of certain extensions and a certain mime-type.	1.5.0
	extensions	Contains a list of file extensions (separated by spaces) that the application requests it be registered to handle.	1.5.0
	mime-type	Contains the mime-type that the application requests it be registered to handle.	1.5.0
related-content		Describes an additional piece of related content that may be integrated with the application.	1.5.0
	href	A URL pointing to the related content.	1.5.0	yes
update		The update element is used to indicate the preferences for how application updates should be handled by the JNLP Client.	1.6.0
	check	Indicates the preference for when the JNLP Client should check for updates. It can be always, timeout, or background..	1.6.0
	policy	Indicates the preference for how the JNLP Client should handle an application update when it is known an update is available before the application is launched. It can be always, prompt-update, or prompt-run.	1.6.0
			1.0
security		This element can be used to request enhanced permissions.	1.0
all-permissions		Requests that the application be run with all permissions.	1.0
j2ee-application-client-permissions		Requests that the application be run with a permission set that meets the security specifications of the J2EE Application Client environment.	1.0
			1.0
resources		Describes all the resources that are needed for an application.	1.0	yes
	os	Specifies the operating system for which the resources element should be considered.	1.0
	arch	Specifies the architecture for which the resources element should be considered.	1.0
	locale	Specifies that the locales for which the resources element should be considered.
java (or java se)		Specifies what version(s) of Java to run the application with.	1.6.0 (java)
	version	Describes an ordered list of version ranges to use.	1.0	yes
	href	The URL denoting the supplier of this version of java, and where it may be downloaded from.	1.0
	java-vm-args	Indicates an additional set of standard and non-standard virtual machine arguments that the application would prefer the JNLP Client to use when launching Java.	1.0
	initial-heap-size	Indicates the initial size of the Java heap.	1.0
	max-heap-size	Indicates the maximum size of the Java heap.	1.0
jar		Specifies a JAR file that is part of the application'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 contains the class containing the main method of the application.	1.0
	download	Can be used to indicate this jar may be downloaded lazily, or when needed.	1.0
	size	Indicates 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
nativelib		Specifies a JAR file that contains native libraries in it's 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 may be downloaded lazily.	1.0
	size	Indicates 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		Contains pointer to an additional component-desc or installer-desc to be used with this application.	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	Describes 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 may be downloaded eagerly or lazily.	1.0
	part	Denotes the name of a part in this jnlp file to include the extension in.	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 indicated 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 it will be set to.	1.0	yes
			1.0
		Note: A jnlp file must contain one of application-desc, applet-desc, component-desc, or installer-desc	1.0	yes
applicaation-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 main.	1.0
applet-desc		Denotes this is the jnlp file for an applet.	1.0
	main-class	This is 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 into 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 supports encoding of JNLP files in any character encoding supported by the Java platform. For more information on character encoding in Java, 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"?>

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Note: The XML prolog itself must be UTF-8-encoded.

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Once you've completed to preceding steps, you are ready to write a Web page that gives users access to your application. Adding a link to your application in a Web page for users with Java Web Start already installed is simple; however, you must also design your Web page for users that might not have Java Web Start installed.

Adding the Basic Link to the JNLP File

In order to enable your users to launch the application from a Web page, you must include a link to the application's JNLP file from that Web page. To add this link, you use the standard HTML link syntax, with the href attribute specifying the location of the JNLP file:

<a href="Notepad.jnlp">Launch Notepad Application</a>

Assuming Java Web Start is installed on the client computer, when the user clicks this link, Java Web Start executes the application based on the instructions in the JNLP file.

Adding the Link when Java Web Start is not Installed

For users who might not have Java Web Start installed, you must write scripts in your Web page to:

1. Detect which browser the user has.
2. Detect whether Java Web Start is installed.
3. If Java Web Start is not installed, either auto-install it, or direct the user to a download page.

For more information and sample scripts to use for these steps, see the Java Web Start Guide.