Trail: Deployment
Lesson: Java Web Start
Deploying Java Web Start Applications
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Deploying Java Web Start Applications
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.

Setting up the Web Server

Before you can deploy an application with Java Web Start over the Web, you must ensure that the Web server you are using can handle JNLP files.

Configure the Web server so that files with the .jnlp extension are set to the application/x-java-jnlp-file MIME type.

How you set the JNLP MIME type depends on the Web server you are using. For example, for the Apache Web server, you simply add the line

application/x-java-jnlp-file JNLP
to the mime.types file.

For other Web servers, check the documentation for instructions on setting MIME types.

Creating the JNLP File

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.

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).

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"?>

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

Placing the Application on the Web Server

The next step in deploying your application with Java Web Start is as simple as placing all the application's JAR files and the JNLP file on the Web server. You must ensure the JAR files are in the locations specified by the href attribute of the jar element in the JNLP file.

Creating the Web Page

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.
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