APPLICATION INSTALLERS

Application installers are a critical piece of many software distribution efforts, particularly for Java desktop applications. The installer is the first part of the application the customer sees. If the installer does not work correctly end users will often give up and refuse to try to troubleshoot the issue. It is thus critical that installation is as painless as possible.

Java Web Start: The default choice

The default choice for installation of Java applications is often Java Web Start. Java Web Start provides the ability to download and launch applications from a web page, and to download and install the correct Java Runtime Environment (JRE) if needed. Once an application has been downloaded it can run offline from a cached version. Java Web Start can also download updated versions of the application jar files, thus fulfilling the roles of installer and automatic updater. Java Web Start is based on, and is an implementation of, the Java Network Launching Protocol (JNLP). Web Start is, of course, produced and supported by Sun Microsystems and is free.

Despite the advantages of Java Web Start it is not the only installer option. In fact, it is technically not an installer at all, as indicated in this passage from the JNLP Specification version 6.0:

1.1 Web-centric Application Model

A JNLP Client is an application or service that can launch applications on a client system from resources hosted across the network. It is not a general installation protocol for software components.

• Installation of Web Start itself, and the right JRE, is sometimes problematic. This very much depends on who your users are.
• Web Start is not designed to handle the 'permanent' installation of files or native components onto a person's machine. Instead it's designed to pull such elements from the internet and cache them on disk. You lose some control of installation location this way, as well as the ability to register subcomponents with the OS and provide conventional uninstallation procedures.
• Web Start launches your application in a generic Java process, rather than naming the process after your application.

Sun has been working hard to solve these issues, particularly the first one. The difficultly lies with users who do not have a JRE installed on their computer. In this case they do not have Java Web Start installed either, so clicking on a JNLP link does not work. Web pages hosting Web Start applications require a difficult, browser-specific block of JavaScript just to allow the user to understand the problem be directed to Sun's site to download a JRE. This is a separate, large download requiring the user to agree to a separate license agreement. In other words, it's a barrier to getting your application running that some users may not cross.

Things are improving. Java Web Start is included in all JREs since version 1.4. Java is standard on Mac OS X, is included with most distributions of Linux, and is now included with most new machines that have Windows pre-installed. Recent estimates state that Java is present on 90% of all desktop machines. Sun also has several initiatives to ease the installation process including a set of browser plugins to handle installation (as opposed to the awkward JavaScript block currently used), a simpler licensing agreement dialog, and a smaller initial download size for the JRE. These welcome initiatives are moving in the right direction, but some will not be released until early 2008, and they will take time to diffuse out into the desktop ecosystem. In the meantime application developers must weight the pros and cons of Java Web Start vs. a more conventional application installation. For Java applications to compete against native desktop applications it is important not to assume that Java must be presented in some completely platform-native way and cannot use a conventional application installer. Of course, it is possible to have multiple ways to use an application available from the same site, including a Java Web Start launching button and an option to download and run a conventional installer. This way users can choose the technique that works for them.

Despite the issues with Java Web Start, it has the built-in capability to automatically update your application using either timestamps or version numbers. Auto-updating is an important function, and with Web Start this is built-in and free.

Toolsets for deployment: Launchers, Installers, & Installer Generators

• Launcher:    A wrapper around a JAR file that launches a process and runs the Java application within that process.
• Installer:    A program that writes a Java application and all files needed to run it (including a launcher) to disk, and performs any OS configuration desired (such as creating desktop icons).
• Installer Generator:    Creates native installation programs (and native launchers) for multiple platforms.

Launchers

If your application runs in it's own process (such as a standard desktop application) then a launcher provides several benefits. It can check the JRE version to ensure there are no version conflicts before launching the Java application within the JRE. It can also use native code to rapidly present a splash screen before the JRE loads, though as of Java 1.6 this is also a built-in feature of the JRE.

One of the most important benefits of a launcher is the ability to register itself as a standard application within the operating system (OS) so the OS grant special permissions to your application, rather than to the Java runtime. It can name the OS process after your application, and register your company as the publisher of the application. This means users can identify the process running your application as yours, rather than seeing multiple generic "java" processes running on their computer. This is especially important when the OS gives security warnings related to the application, or if the user needs to find the application process in the the process list (task list in Windows). Obviously, if your application needs special permissions to run and the user becomes confused about which application is making the request they will probably deny the request, preventing your application from operating correctly.

There are many programs that can generate a native launcher for your Java application. However, most installer generators (see below) will also create a launcher. Buying a separate launcher generator is not usually necessary.

Installers

• Detect installed JREs to ensure the proper JRE is present, and download and install it if necessary.
• Create desktop icons and OS-level menu items for launching the program.
• Register the program and its uninstaller with the OS.
• Allow the user to configure the installation directories.
• Require the user to agree to a license agreement.
• Give the user multiple configuration options (such as languages, minimal vs. full install, etc.).
• Write configuration data to the user directory, registry, etc.
• Run aribitrary scripts during installation.
• Install a program as a service.

There are a number of installer programs written in Java. That is, the installer itself is a Java program. This creates an obvious problem: if the user does not have Java on their machine they cannot run the installer. This is the classic "install the installer" problem, and it is the reason why the installation program the user downloads should be written in native code for their platform. The installer can then detect the user's JRE and download and install a correct JRE before launching your Java application. Java Web Start suffers from the install the installer problem. The way to create a native installation program for every platform is to use an installer generator.

Installer Generators

An installer generator is an application that creates an installer for your software product. The best installer generators will create a native launcher and a native installer for every major platform. They should also be easy to integrate into your build process, usually by providing an Ant task or Maven Mojo. Once configured, you should be able to run a build that compiles and packages your Java application and then creates a native installer for every major platform. This should happen automatically on a full build with no manual intervention required. Some installer generators even create a web page for you to help you distribute the correct installer to each visitor.

A critical point to note is that, unlike Java Web Start, most installer genertors do not provide automatic updating out-of-the-box. Instead it must be added using an additional tool and, quite often, custom programming.

Links

Java Web Start Info and Documentation

Java Web Start Controversies

Open-source Launchers & Installers

Commercial Installer Generators

One final note: we do not advocate using any particular technology. Rather, we prefer to put all of the available options on the table for you to evaluate. Enjoy.