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# Overview of Java Web Start Technology

This section includes the following topics:

- Introduction to Java Web Start
- Benefits of Java Web Start
- Security Considerations
- Where to Find Java Web Start
- Using Java Web Start
  - Launching from a Web Browser
  - Launching from Desktop Icons and the Start Menu (Microsoft Windows and Linux Running GNOME 2.0+)
  - Using Java Web Start Software Behind a Proxy Server or Firewall

## Introduction to Java Web Start

Java Web Start is an application-deployment technology that enables your users to launch full-featured applications with a single click from any web browser. Users can download and launch applications without going through complicated installation procedures.

With Java Web Start, your users launch applications by clicking a web page link. If the application is not present on their computer, Java Web Start automatically downloads all necessary files. It then caches the files on the computer so that the application is always ready to be relaunched anytime the user wants — either from an icon on the desktop or from the browser link. No matter which method is used to launch the application, the most current version of the application is always presented.

The technology underlying Java Web Start is the Java Network Launching Protocol & API (JNLP). This technology was developed through the Java Community Process (JCP). Java Web Start is the reference implementation (RI) for the JNLP specification. The JNLP technology defines, among other things, the JNLP file, which is a standard file format that describes how to launch an application. The JNLP specification is available at JSR 56: Java Network Launching Protocol and API.

## Benefits of Java Web Start

From a technology standpoint, Java Web Start has a number of key benefits that make it an attractive platform to use for deploying applications.

The benefits include the following:

- Java Web Start is built exclusively to launch applications written to the Java Platform, Standard Edition. Thus, a single application can be made available on a web server and then deployed on a wide variety of platforms, including Windows, Linux, and macOS.

- Java Web Start supports multiple revisions of the Java Platform, Standard Edition. Thus, an application can request a particular version of the platform it requires, such as Java SE 8. Several applications can run at the same time on different platform revisions without causing conflicts.

- Java Web Start enables applications to be launched independently of a web browser. This can be used for off-line operation of an application, where launching the application through the browser is inconvenient or impossible. The application can also be launched through desktop shortcuts, making launching the web-deployed application similar to launching a native application.

- Java Web Start takes advantage of security features of the Java Platform. Sandbox applications are run in a protective environment with restricted access to local disk and network resources. Users must also agree to run the application the first time it is launched.

- Applications launched with Java Web Start are cached locally. Thus, an already-downloaded application is launched similar to a traditionally installed application.

## Security Considerations

Java Web Start allows you to run code from the internet. Although there are mechanisms in place, such as HTTPS, that attempt to validate the provenance of code obtained from the internet, it's not always possible to do so. Therefore Java Web Start relies on code signing to determine if the code comes from a trusted party.

Unsigned code will be rejected, and after signature verification, the user will be prompted to determine if the code signer should be trusted. It is very important that no unsigned code or code from a nontrusted signer be granted run permission. This means that users must pay attention to the security warnings and prompts. See Security and Code Signing .

You can use the Deployment Rule Set (DRS) feature to prevent a user the ability to decide whether a code signer should be trusted. Instead, an organization can specify a security policy that determines this. Consequently, if your organization uses a DRS, you can avoid presenting dialogs to end users. Trusted signers can have their code launched without prompts while untrusted and unsigned code can be denied without prompts.

You can use the Exception Site List feature to provides a way for users to run Rich Internet Applications (RIAs) that otherwise would be blocked by security checks. The exception site list contains URLs for sites that host RIAs that users want to run. RIAs that are launched from sites in the exception site list are allowed to run with the appropriate security prompts.

Java Web Start Users should apply all critical patch updates for JRE 8 (specifically, the JRE version that launches Java Web Start). Turning on auto-update can help you keep your JRE up-to-date.

There are alternative providers that can manage Java Web Start applications and JNLP, such as IcedTea-Web. Oracle makes no claims as to whether these providers perform all the security checks that the JDK performs. If you choose to rely on those providers, carefully evaluate them as you would any new technology that you plan to run in your systems. Oracle recommends that you check that these providers do not allow unsigned code to run and that they request user acceptance with information from the signature before trusting signed code.

## Where to Find Java Web Start

Java Web Start is included in the Java Platform, Standard Edition development kit (JDK) and Java Runtime Environment (JRE), and includes the security features of the Java platform.

## Using Java Web Start Software

Java Web Start allows you to launch Java-technology-based applications directly from the Web. An application can be launched in three different ways:

- From a Web browser by clicking on a link.
- From desktop icons or the Start Menu.
- From the Java Cache Viewer

Regardless of which way is used, Java Web Start will connect back to the Web server each time an application is launched to check whether an updated version of the application is available.

### Launching from a Web Browser

Point your web browser to a page with a link to a JNLP application, and click that link.

A security dialog box will pop up with information about the origin of the application based on who digitally signed the code, and the level of access requested. The application will run only if you decide to trust the vendor.

That is really all there is to using Java Web Start, but how does it work? The HTML links that launch the applications are, in fact, standard HTML links. However, instead of pointing to another web page, they link to a special configuration file called a JNLP file. The web browser examines the file extension or the MIME type of the file, and sees that it belongs to Java Web Start. It then launches Java Web Start with the downloaded JNLP file as an argument. Java Web Start proceeds with downloading, caching, and running the application as directed by the JNLP file.

### Launching from Desktop Icons and the Start Menu (Microsoft Windows and Linux Running GNOME 2.0+)

Java Web Start technology can automatically create shortcuts for your application on the desktop and in the Start Menu for web-deployed applications developed with Java technology. You can use the Java Control Panel to control the shortcut settings. Shortcuts can also be added by using the Java Web Start Cache Viewer, using the install shortcut menu item.

### Using Java Web Start Software Behind a Proxy Server or Firewall

Java Web Start software must be configured with the correct proxy settings in order to launch applications from outside your firewall. Java Web Start software automatically tries to detect the proxy settings from the default browser on your system. Java Web Start technology supports most web proxy auto-configuration scripts. It can detect proxy settings in almost all environments.

You can also use the Java Web Start Control Panel to view or edit the proxy configuration. Refer to the Java Control Panel for more details.

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