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JNLP File Syntax

This section covers the following topics:

• Introduction
• Examples of a JNLP File
  • Basic JNLP File
  • JNLP File with Application Customizations
• JNLP Elements
  • jnlp Element
  • information Element
  • security Element
  • update Element
  • resources Element
  • application-desc Element
  • applet-desc Element
  • component-desc Element
  • installer-desc Element

Introduction

The format used in this release is that specified in the Java Network Launching Protocol & API Specification (JSR-56) version 8.20. This document describes the most commonly used elements of a JNLP file. For a complete description of the format, refer to the specification.

Examples of a JNLP File

For a basic application that does not require a lot of customization, the JNLP file can be simple. For more complex applications, additional elements can be added to the JNLP file.

The elements are described in JNLP Elements.

Basic JNLP File

This example shows a simple JNLP file. The root element is jnlp, which has two subelements: resources and application-desc.

<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="8">
    <resources>
        <jar href="https://docs.oracle.com/javase/tutorialJWS/samples/deployment/NotepadJWSProject/Notepad.jar" />
    </resources>
    <application-desc main-class="Notepad"/>
</jnlp>

JNLP File with Application Customizations

This example shows the basic outline of the JNLP file with settings for application attributes. The root element is jnlp, which has four subelements: information, security, resources, and application-desc. In addition, Java Web Start also supports launching applets by using the applet-desc element.

<?xml version="1.0" encoding="utf-8"?>
<!-- JNLP File for SwingSet2 Demo Application -->
<jnlp
  spec="6.0+"
  codebase="http://my_company.com/jaws/apps"
  href="swingset2.jnlp">
  <information>
    <title>SwingSet2 Demo Application</title>
    <vendor>Sun Microsystems, Inc.</vendor>
    <homepage href="docs/help.html"/>
    <description>SwingSet2 Demo Application</description>
    <description kind="short">A demo of the capabilities 
    of the Swing Graphical User Interface.</description>
    <icon href="images/swingset2.jpg"/>
    <icon kind="splash" href="images/splash.gif"/>
    <offline-allowed/> 
    <association mime-type="application-x/swingset2-file"  extensions="swingset2"/> 
    <shortcut online="false" install="false">
      <desktop/>
      <menu submenu="My Corporation Apps"/>
    </shortcut>
  </information>
  <information os="linux">   
    <title> SwingSet2 Demo on Linux </title>
    <homepage href="docs/linuxhelp.html">
  </information>
  <security>
      <all-permissions/>
  </security>
  <resources>
    <j2se version="1.6+" java-vm-args="-esa -Xnoclassgc"/>
    <jar href="lib/SwingSet2.jar"/>
  </resources>
  <application-desc main-class="SwingSet2"/>
</jnlp> 

JNLP Elements

jnlp Element

spec attribute: This attribute must be 1.0 or higher to work with this release. The default value is "1.0+". Thus, it can typically be omitted. Note that this version supports spec versions 1.0, 1.5.0, 6.0, 6.0.10, 6.0.18, 7.0, and 8.20. A jnlp file specifying spec="8.20+" will work with this version, but not previous versions of Java Web Start.

codebase attribute: All relative URLs specified in href attributes in the JNLP file are using this URL as a base.

href attribute: This is a URL pointing to the location of the JNLP file itself.

information Element

os attribute: This attribute contains a list of operating system names for this element. Read the discussion of the resources element later for a full discussion of the os attribute.

title element: The name of the application.

vendor element: The name of the vendor of the application.

homepage element: Contains a single attribute, href, which is a URL locating the home page for the Application. It is used by the Java Application Cache Viewer to point the user to a Web page where more information about the application can be found.

description element: A short statement about the application. Description elements are optional. The kind attribute defines how the description should be used. It can have one of the following values:

• one-line: If a reference to the application is going to appear on one row in a list or a table, this description will be used.
• short: If a reference to the application is going to be displayed in a situation where there is room for a paragraph, this description is used.
• tooltip: If a reference to the application is going to appear in a tooltip, this description is used.

Only one description element of each kind can be specified. A description element without a kind is used as a default value. Thus, if Java Web Start needs a description of kind short, and it is not specified in the JNLP file, then the text from the description without an attribute is used.

All descriptions contain plain text. No formatting, such as with HTML tags, is supported.

icon element: Contains an HTTP URL to an image file in either GIF, JPEG, ICO, or PNG format. The icons are used to represents the application

• during launch when Java Web Start presents the application to the user;
• in the Java Application Cache Viewer;
• in desktop shortcuts.

A 64x64 icon is shown during download; in the Java Application Cache Viewer and in desktop shortcuts a 32x32 icon is used. Java Web Start automatically resizes an icon to the appropriate size.

Optional width and height attributes can be used to indicate the size of the images.

The optional kind attribute can have one of the following values:

• default: The specified image is used in the Java Application Cache Viewer. It is also used if an icon element with a particular kind attribute has not been specified. Not specifying the kind attribute is the same as specifying it with the default value.
• splash: The specified image is used as the splash image on the second and subsequent launches of the application. During the initial launch of the application, before resources are downloaded, the default splash image is used.
• shortcut: The specified image is used in desktop shortcuts.

A JNLP file can contain multiple icon elements that differ by their kind attribute. This enables you to specify different icon images for your application.

offline-allowed element: The optional offline-allowed element indicates if the application can be launched offline.

If offline-allowed is specified, then the application can be launched offline by the Java Application Cache Viewer, and shortcuts can be created which launch the application offline.

If an application is launched offline, it will not check for updates and the API call BasicService.isOffline() will return true.

The offline-allowed element also controls how Java Web Start checks for an update to an application. If the element is not specified—i.e., the application is required to be online to run—Java Web Start will always check for an updated version before launching the application. And if an update is found, the new application will be downloaded and launched. Thus, it is guaranteed that the user always runs the latest version of the application. The application, however, must be run online.

If offline-allowed is specified, Java Web Start will also check to see if an update is available. However, if the application is already downloaded the check will timeout after a few seconds, in which case the cached application will be launched instead. Given a reasonably fast server connection, the latest version of the application will usually be run, but it is not guaranteed. The application, however, can be run offline.

shortcut element: The optional shortcut element can be used to indicate an application's preferences for desktop integration. The shortcut element and its sub-elements provide hints that the JNLP Client may or may not use. The shortcut element can contain the optional online and install attributes, and the two optional sub-elements, desktop and menu.

association element: The optional association element is a 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. The association element must have the extensions and mime-type attributes. If the association element is included, either the offline-allowed element must also be included, or the href attribute must be set for the jnlp element to ensure that the application can be located and run.

related-content element: The optional related-content element describes an additional piece of related content, such as a readme file, help pages, or links to registration pages, as a hint to a JNLP Client. The application is asking that this content be included in its desktop integration. The related-content element has a mandatory href and title attribute. It can contain any of the following two sub-elements:

• description element: A short description of the related content.
• icon element: The icon can be used by the JNLP Client to identify the related content to the user.

security Element

Each sandbox application is run in a restricted execution environment, similar to the Applet sandbox. The security element can be used to request unrestricted access.

If the all-permissions element is specified, the application will have full access to the client machine and local network. All JAR files must be signed. The user is prompted to accept the certificate and agree to run the application.

update Element

The update element is used to indicate the preferences for how application updates should be handled by Java Web Start.

The update element can contain the following two optional attributes:

check attribute: The check attribute indicates the preference for when the JNLP Client should check for updates, and can have one of the three values: "always", "timeout", and "background"

A value of "always" means to always check for updates before launching the application.

A value of "timeout" (default) means to check for updates until timeout before launching the application. If the update check is not completed before the timeout, the application is launched, and the update check will continue in the background.

A value of "background" means to launch the application while checking for updates in the background.

policy attribute: The policy attribute 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, and can have one of the following three values: "always", "prompt-update", and "prompt-run"

A value of "always" (default) means to always download updates without any prompt.

A value of "prompt-update" means to ask the user if he/she wants to download and run the updated version, or launch the cached version.

A value of "prompt-run" means to ask the user if he/she wants to download and run the updated version, or cancel and abort running the application.

For example:

resources Element

The resources element is used to specify all the resources, such as Java class files, native libraries, and system properties, that are part of the application. A resource definition can be restricted to a specific operating system, architecture, or locale using the os, arch, and locale attributes.

The os attribute contains a list of operating system names for a resource. For example, you could use multiple resources definitions, with different os attributes, to supply a native library for multiple operating systems.

The os attribute contains a list of operating system names separated by spaces. At runtime, the os values are compared with the beginning of the os.name system property to find a match. For example, an os attribute value of "Windows" matches both "Windows 8" and "Windows 10" operating systems.

If you wish to list an operating system whose name contains a space, use a backslash to indicate that the space is part of the operating system name. The following example will specifically match "Windows 8" and "Windows 10":

<resources os="Windows\ 8 Windows\ 10">
    <jar href="hello.jar"/>
</resources>

The resources element has six different possible subelements: jar, nativelib, j2se, property, package, and extension. The package and extension elements are not discussed in this developer's guide.

A jar element specifies a JAR file that is part of the application's classpath. For example:

<jar href="myjar.jar"/>

The jar file will be loaded into the JVM using a ClassLoader object. The jar file will typically contain Java classes that contain the code for the particular application, but can also contain other resources, such as icons and configuration files, that are available through the getResource mechanism.

A nativelib element specifies a JAR file that contains native libraries. For example:

<nativelib href="lib/windows/corelib.jar"/>

The JNLP client must ensure that each file entry in the root directory of the JAR file (i.e., /) can be loaded into the running process using the System.loadLibrary method. Each entry must contain a platform-dependent shared library with the correct naming convention, e.g., *.dll on Windows or lib*.so on Solaris/Linux. The application is responsible for doing the actual call to System.loadLibrary.

Native libraries would typically be included in a resources element that is geared toward a particular operating system and architecture. For example:

<resources os="SunOS" arch="sparc">
    <nativelib href="lib/solaris/corelibs.jar"/>
</resources>

By default, jar and nativelib resources will be downloaded eagerly, i.e., they are downloaded and available locally to the JVM running the application before the application is launched. The jar and nativelib elements also allow a resource to be specified as lazy. This means the resource does not have to be downloaded onto the client system before the application is launched.

The download attribute is used to control whether a resource is downloaded eagerly, lazily, or contains a custom progress implementation. For example:

<jar href="sound.jar" download="lazy"/>
<nativelib href="native-sound.jar" download="eager"/>
<jar href="progress.jar" download="progress"/>

A jar denoted with download="progress" will be downloaded eagerly, and may be used to indicate progress while downloading other resources.

The j2se element specifies what Java Platform Standard Edition Runtime Environment (JRE) versions an application is supported on, as well as standard parameters to the Java Virtual Machine. If several JREs are specified, this indicates a prioritized list of the supported JREs, with the most preferred version first. For example:

<j2se version="1.3" initial-heap-size="64m" max-heap-size="128m"/>
<j2se version="1.4.2+" href="http://java.sun.com/products/autodl/j2se" java-vm-args="-esa -Xnoclassgc"/>

The version attribute refers, by default, to a platform version (specification version) of the Java Platform Standard Edition. Currently defined platform versions are 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, and 1.8. (A platform version will not normally contain a micro version number; e.g., 1.4.2.)

Exact product versions (implementation versions) may also be specified. by including the href attribute. For example, 1.3.1_07, 1.4.2, or 1.5.0-beta2 by Sun Microsystems, Inc. For example,

<j2se version="1.4.2" href="http://java.sun.com/products/autodl/j2se"/

or

<j2se version="1.4.2_04" href="http://java.sun.com/products/autodl/j2se"/>

If a platform version is specified (i.e., no href attribute is provided), Java Web Start will not consider an installed non-FCS (i.e., milestone) JRE as a match. E.g., a request of the form

<j2se version="1.4+"/>

would not consider an installed 1.4.1-ea or 1.4.2-beta JRE as a match for the request. Starting with 1.3.0, a JRE from Sun Microsystems, Inc., is by convention a non-FCS (milestone) JRE if there is a dash (-) in the version string.

The java-vm-args attribute of the j2se element specifies a preferred set of virtual machine arguments to use when launching java.

Note: Arguments are used only if they are considered secure. See the secure properties Note.

The following java-vm-args are supported by this version:

-d32                            /* use 32-bit data model if available */
-client                         /* to select the "client" VM */
-server                         /* to select the "server" VM */
-verbose                        /* enable verbose output */
-version                        /* print product version and exit */
-showversion                    /* print product version and continue */
-help                           /* print this help message */
-X                              /* print help on non-standard options */
-ea                             /* enable assertions */
-enableassertions               /* enable assertions */
-da                             /* disable assertions */
-disableassertions              /* disable assertions */
-esa                            /* enable system assertions */
-enablesystemassertions         /* enable system assertions */
-dsa                            /* disable system assertione */
-disablesystemassertions        /* disable system assertione */
-Xmixed                         /* mixed mode execution (default) */
-Xint                           /* interpreted mode execution only */
-Xnoclassgc                     /* disable class garbage collection */
-Xincgc                         /* enable incremental gc. */
-Xbatch                         /* disable background compilation */
-Xprof                          /* output cpu profiling data */
-Xdebug                         /* enable remote debugging */
-Xfuture                        /* enable strictest checks */
-Xrs                            /* reduce use of OS signals */
-XX:+ForceTimeHighResolution    /* use high resolution timer */
-XX:-ForceTimeHighResolution    /* use low resolution (default) */
-XX:+PrintGCDetails             /* Gives some details about the GCs */
-XX:+PrintGCTimeStamps          /* Prints GCs times happen to the start of the application */
-XX:+PrintHeapAtGC              /* Prints detailed GC info including heap occupancy */
-XX:+PrintTenuringDistribution  /* Gives the aging distribution of the allocated objects */
-XX:+TraceClassUnloading        /* Display classes as they are unloaded */
-XX:+CMSClassUnloadingEnabled   /* It needs to be combined with -XX:+CMSPermGenSweepingEnabled */
-XX:+CMSIncrementalPacing       /* Automatic adjustment of the incremental mode duty cycle */
-XX:+UseConcMarkSweepGC         /* Turns on concurrent garbage collection */
-XX:-ParallelRefProcEnabled
-XX:+DisableExplicitGC          /* Disable calls to System.gc() */
-XX:+UseG1GC
-XX:+HeapDumpOnOutOfMemoryError
-XX:-TransmitErrorReport
-XstartOnFirstThread
-XX:+UseStringDeduplication
-XX:+PrintStringDeduplicationStatistics
-XX:+UseParallelOldGC
-XX:-UseParallelOldGC
-XX:+UseParallelOldGCCompacting
-XX:-UseParallelOldGCCompacting
-XX:+UseParallelGC
-XX:-UseParallelGC
-XX:+UseGCTimeLimit
-XX:-UseGCTimeLimit
-XX:+UseGCOverheadLimit
-XX:-UseGCOverheadLimit
-XX:+ScavengeBeforeFullGC
-XX:-ScavengeBeforeFullGC
-XX:+UseParallelScavenge
-XX:-UseParallelScavenge

Plus any argument starting with one of the following:

-ea:                                 /* enable assertions for classes ... */
-enableassertions:                   /* enable assertions for classes ... */
-da:                                 /* disable assertions for classes ... */
-disableassertions:                  /* disable assertions for classes ... */
-verbose:                            /* enable verbose output */
-Xmn                                 /* set the young gen size; this is
                                        an unspecified and undocumented
                                        JVM option being added here only
                                        as a convenience to end users    */
-Xms                                 /* set initial Java heap size */
-Xmx                                 /* set maximum Java heap size */
-Xss                                 /* set java thread stack size */
-XX:NewRatio                         /* set Ratio of new/old gen sizes */
-XX:NewSize                          /* set initial size of new generation */
-XX:MaxNewSize                       /* set max size of new generation */
-XX:PermSize                         /* set initial size of permanent gen */
-XX:MaxPermSize                      /* set max size of permanent gen */
-XX:MaxHeapFreeRatio                 /* heap free percentage (default 70) */
-XX:MinHeapFreeRatio                 /* heap free percentage (default 40) */
-XX:-UseSerialGC                     /* use serial garbage collection */
-XX:ThreadStackSize                  /* thread stack size (in KB) */
-XX:MaxInlineSize                    /* set max num of bytecodes to inline */
-XX:ReservedCodeCacheSize            /* Reserved code cache size (bytes) */
-XX:MaxDirectMemorySize              /* set maximum direct memory size */
-XX:PrintCMSStatistics               /* If > 0, Print statistics about the concurrent collections */
-XX:SurvivorRatio                    /* Sets the ratio of the survivor spaces */
-XX:MaxTenuringThreshold             /* Determines how much the objects may age */
-XX:CMSMarkStackSize
-XX:CMSMarkStackSizeMax
-XX:CMSIncrementalDutyCycleMin       /* The percentage which is the lower bound on the duty cycle */
-XX:ParallelCMSThreads
-XX:ParallelGCThreads                /* Sets the number of parallel GC threads */
-XX:CMSInitiatingOccupancyFraction   /* Sets the threshold percentage of the used heap */
-XX:+UseCompressedOops               /* Enables compressed references in 64-bit JVMs */
-XX:GCPauseIntervalMillis
-XX:MaxGCPauseMillis                 /* A hint to the virtual machine to pause times */
-XX:+CMSIncrementalMode              /* Enables the incremental mode */
-XX:MaxMetaspaceSize                 /* Sets an upper limit on memory used for class metadata */
-XX:StringDeduplicationAgeThreshold
-XX:GCTimeLimit
-XX:GCHeapFreeLimit

The property element defines a system property that will be available through the System.getProperty and System.setProperties methods. It has two required attributes: name and value. For example:

Properties set in the JNLP file will normally be set by Java Web Start after the VM is started but before the application is invoked. Some properties are considered "secure" properties and can be passed as -Dkey=value arguments on the java invocation command line. The following properties are predefined secure properties and will be passed to the VM in this way:

    sun.java2d.noddraw,
    javaws.cfg.jauthenticator,
    swing.useSystemFontSettings,
    swing.metalTheme,
    http.agent,
    http.keepAlive,
    sun.awt.noerasebackground,
    sun.java2d.opengl,
    sun.java2d.d3d,
    java.awt.syncLWRequests,
    java.awt.Window.locationByPlatform,
    sun.awt.erasebackgroundonresize,
    sun.awt.keepWorkingSetOnMinimize,
    swing.noxp,
    swing.boldMetal,
    awt.useSystemAAFontSettings,
    sun.java2d.dpiaware,
    sun.awt.disableMixing,
    sun.lang.ClassLoader.allowArraySyntax,
    java.awt.smartInvalidate"
    apple.laf.useScreenMenuBar,
    java.net.preferIPv4Stack,
    java.util.Arrays.useLegacyMergeSort",
    sun.locale.formatasdefault,
    sun.awt.enableExtraMouseButtons,
    com.sun.management.jmxremote.local.only,
    sun.nio.ch.bugLevel,
    sun.nio.ch.disableSystemWideOverlappingFileLockCheck,
    jdk.map.althashing.threshold
    javaplugin.lifecycle.cachesize

New secure properties can also be defined as needed by prefixing the property name with "jnlp." or "javaws.".

Note: To be considered secure, property names and values must meet the following requirements:

• The string does not contain either the double quote (") character or percent (%) character.
• The string does not contain any character less than the space (' ', 0x20) character or greater than the tilde (~, 0x17E) character.
• The final character of the string is not a backslash (\).

System properties set in an unsigned JNLP file will only be set by Java Web Start if they are considered secure.

For information about properties that affect the behavior of Java Web Start applications, see Properties That Affect the Behavior of Rich Internet Applications.

application-desc Element

The application element indicates that the JNLP file is launching an application (as opposed to an applet). The application element has an optional attribute, main-class, which can be used to specify the name of the application's main class, i.e., the class that contains the public static void main(String argv[]) method where execution must begin.

The main-class attribute can be omitted if the first JAR file specified in the JNLP file contains a manifest file containing the main class.

Arguments can be specified to the application by including one or more nested argument elements. For example:

<application-desc main-class="Main">
<argument>arg1</argument>
<argument>arg2</argument>
</application-desc>

The (optional) progress-class attribute can be used to indicate that the class of this name implements the javax.jnlp.DownloadServiceListener interface. This class may be loaded first and used to indicate the progress of other resources being downloaded and verified.

applet-desc Element

Java Web Start has support for launching Java applets. This support provides easy migration of existing code to Java Web Start.

An applet is launched using the applet-desc element instead of the application-desc element. For example:

<applet-desc
documentBase="http://..."
name="TimePilot"
main-class="TimePilot.TimePilotApp"
width="527"
height="428">
<param name="key1" value="value1"/>
<param name="key2" value="value2"/>
</applet-desc>

The JAR files that make up the applet are described using the resources element as for applications. The documentBase must be provided explicitly since a JNLP file is not embedded in an HTML page. The rest of the attributes correspond to the respective HTML applet tag elements.

The main-class attribute is used instead of the code attribute. The main-class attribute is assigned the name of the Applet class (without the .class extension). This attribute can be omitted if the Applet class can be found from the Main-Class manifest entry in the main JAR file.

The (optional) progress-class attribute can be used to indicate that the class of this name implements the javax.jnlp.DownloadServiceListener interface. This class may be loaded first and used to indicate the progress of other resources being downloaded and verified.

Note: Applets must be packaged in JAR files in order to work with Java Web Start.

component-desc Element

The component-desc element denotes that this jnlp file is not an application or an applet but an extension that can be used as a resource in an application, applet or another extension.

A component extension is typically used to factor out a set of resources that are shared between multiple applications or that have separate security needs.

The (optional) progress-class attribute can be used to indicate that the class of this name implements the javax.jnlp.DownloadServiceListener interface. This class may be loaded first and used to indicate the progress of other resources being downloaded and verified.

installer-desc Element

The installer-desc element denotes that this jnlp file is an installer extension that defines an application that will be run only once, the first time this extension jnlp file is used in an application, applet or another extension.

An installer extension is typically used to install platform specific native code that requires a more complicated setup than simply loading a native library into the VM.

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