Run a JNLP

Run a JWS/JNLP application in the browser

This quickstart tutorial will take you step by step on how to run your JNLP app (also known as Java Web Start application) in the browser with CheerpJ.

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JNLP Runner

You will need:

  • The application .jnlp file.
  • An HTML file where your Java app will be wrapped.
  • A simple HTTP server to test your webpage locally.

1. The .jnlp file

The .jnlp file contains the specifics of how to launch your Java application. The usual pipeline starts when this file is triggered from a website so it is passed to the user’s local JNLP client which downloads the application .jar files and further resources. Finally, the app is executed with the local JRE installation. With CheerpJ it is possible to run this application in the browser sandbox, no Java installation required.

Your .jnlp file might look something like the example below. There are three essential elements you need to find:

  1. The .jar files specified under the <resources> element, usually indicated with a <jar> or <nativelib> tags.
  2. Your application type. Look for an <application-desc> or <applet-desc> tag.
  3. You may need the codebase URL given by <jnlp>.
example.jnlp
<?xml version="1.0" encoding="utf-8"?>
<!-- JNLP Example -->
<jnlp
  spec="1.0+"
  codebase="code-base-url"
  href="example.jnlp">
  <information>
    <title>Your application name</title>
    <vendor>Vendor name</vendor>
    <homepage href="home-page-url"/>
    <description>Description of your Java application</description>
    <description kind="short">Another description of your Java application</description>
    <icon href="image-url"/>
    <icon kind="icon-name" href="image-url"/>
    <offline-allowed/>
  </information>
  <security>
      <all-permissions/>
  </security>
  <resources>
    <j2se version="1.4+" initial-heap-size="64m" max-heap-size="640m"/>
    <jar href="my_application_archive.jar"/>
    <jar href="lib/my_dependency.jar"/>
    <property name="key" value="overwritten"/>
  </resources>
  <application-desc main-class="com.application.MyClassName"/>
</jnlp>

2. Create a project directory

Once you have identified where the <jar> or <nativelib> tags are in your JNLP, you can simply download these JARs by copying and pasting their URLs in the browser’s navigation bar. If these URLs are relative then build the full URL by appending the codebase URL and the jar URL:

For example:

code-base-url/my_application_archive.jar
code-base-url/lib/my_dependency.jar

Please create a directory for your project and place the JARs you just downloaded inside this folder, remember to keep the same directory structure as shown in your .jnlp.

For example:

Terminal window
mkdir -p directory_name/lib

Once you moved the JARs it should look like this:

└── directory_name
    ├── my_application_archive.jar
    └── lib
        └── my_dependency.jar

3. Create a basic HTML file

3.1 Identify your application type

A JNLP app can be a standalone application or an applet. This is easy to spot on your .jnlp file with the tags <application-desc> or <applet-desc> correspondingly.

We will create a basic HTML file where the CheerpJ runtime will be integrated and the java application displayed. Create this file in the root of the project folder. The way the app is loaded might differ if the application is a standalone app or an applet. The following steps will specify how the HTML will look like for each case.

3.2 If your application is a standalone app

Take a close look at content of <application-desc> and keep the following at hand:

  • The application class name: You can find it at the main-class attribute. This attribute may not be there if the class name is included in the manifest.
  • The application arguments: If any arguments are required, you will find these with the <argument> tag.
Note
If you do not find any of the elements listed above, this means you do not need them to run your application.

Example of an HTML file for an app where the class name is included in the manifest:

index.html
<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>CheerpJ test</title>
    <script src="https://cjrtnc.leaningtech.com/4.1/loader.js"></script>
  </head>
  <body>
    <script>
      (async function () {
        await cheerpjInit();
        cheerpjCreateDisplay(800, 600);
        await cheerpjRunJar("/app/my_application_archive.jar");
      })();
    </script>
  </body>
</html>
">

Alternatively, if the class name is in the .jnlp file but not in the manifest, then replace cheerpjRunJar() for cheerpjRunMain():

cheerpjRunMain(
  "com.application.MyClassName",
  "/app/my_application_archive.jar:/app/lib/my_dependency_archive.jar"
);

Any application arguments must be passed to cheerpjRunJar() or cheerpjRunMain(). The /app/prefix is a virtual filesystem mount point that references the root of the web server this page is loaded from.

3.2 If your application is an applet

Take a close look to the <applet-desc> tag on your .jnlp and keep the following at hand:

The HTML for an applet would look like this:

index.html
<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>CheerpJ applet test</title>
    <script src="https://cjrtnc.leaningtech.com/4.1/loader.js"></script>
  </head>
  <body>
    <applet
      archive="my_applet_archive.jar"
      code="com.applet.MyClassName"
      height="900"
      width="900"
    ></applet>
    <script>
      cheerpjInit();
    </script>
  </body>
</html>
">

Any applet parameters should be passed as <param> in the <applet> tag as usual:

<applet
  archive="my_applet_archive.jar"
  code="com.applet.MyClassName"
  height="900"
  width="900"
>
  <param name="paramName" value="paramValue" />
</applet>

In case your users have a native Java plugin installed, you can replace the original HTML tag with a cheerpj- prefixed version. <cheerpj-applet>, <cheerpj-object>, and <cheerpj-embed> are all supported.

Java Applets and Java 8
The method ´cheerpJInit´ runs Java 8 by default if the Java version is not specified. Please notice that if you change the version to Java 11, applets won’t work.

4. Host your page

Your final project directory tree should look similar to:

└── directory_name
    ├── index.html
    ├── my_application_archive.jar
    └── lib
        └── my_dependency.jar

You can now go to the project directory and serve this web page on a simple HTTP server, such as the http-server utility.

Terminal window
cd directory_name
npm install http-server
http-server -p 8080

The end

This is the end of the tutorial. To learn more about running standalone applications and applets with CheerpJ, you can visit the dedicated tutorials:

Application

Applet

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