Java Web App Development and Deployment > Applet Developer's Guide
The content in this guide describes new features in this update release and supersedes all other Java SE 6 guides in the relevant areas (such as Java Web Start, Deployment, Java Plug-in etc.). These guides will be re-written in the next major feature release to narrate a more cohesive story.
JavaTM Plug-In technology (hereafter the "Java Plug-In"), which is included in the Java Runtime Environment, enables Java applets to run in popular web browsers on the desktop. The next-generation Java Plug-In, new in Java SE 6 Update 10, provides powerful new capabilities to applets in the web browser, while improving the overall reliability and functionality of applets in a backward-compatible manner.
The next-generation Java Plug-In offers a completely redesigned architecture. Instead of executing applets in the same operating system process as the web browser, the new plug-in runs one or more Java virtual machine instances ("JVMs") which connect back to the browser for full interoperability with the surrounding web page. This architectural change offers many advantages and enables several new features.
- Improved reliability. The JVM running the applet is isolated from the web browser at the operating system level. If something should go wrong while running the applet, or if an uncooperative applet refuses to shut down, the new Java Plug-In detects and handles the error condition gracefully; the web browser is unaffected.
- Built-in JNLP support. The new plug-in offers the capability to launch applets directly from JNLP files, unifying deployment of Java content both in the browser and out of the browser (via Java Web Start). Developers can now reuse JNLP extensions for advanced functionality including the JavaFX run-time libraries, 3D graphics via OpenGL, and planetary-scale terrain visualization within applets. Applets can now access JNLP APIs for persistent data storage, local file system access, and other useful functionality from sandboxed code.
- Improved user experience. The new Java Plug-In starts applets in the background, so the web browser always remains responsive. Applets appear on the web page as they become ready to run.
- Improved applet lifecycle management. Calls to the applet lifecycle methods
destroy are more deterministic and cross-browser behavior has been improved. The applet class loader cache and the legacy applet lifecycle, required for backward compatibility, are fully supported and the behavior of both has been improved.
- Better large heap support. Historically, the maximum heap size that could be specified for applets via the Java Control Panel has been limited. This limitation is fixed in the new Java Plug-In; applets can now utilize as much heap space as command-line applications.
- Better Windows Vista support. Signed applets running in Protected Mode Internet Explorer on Microsoft's Windows Vista now have the same privileges as normal user applications, eliminating a portability barrier to this platform.
- Per-applet command-line arguments. JVM command-line arguments may be specified in the HTML of the web page on a per-applet basis, providing fine-grained control over options such as the heap size and Java 2D hardware acceleration features.
- Multiple JRE version support. Each individual applet instance may request a different JRE version on which to run. This feature is designed for enterprise customers which prefer to qualify their applets against either a particular JRE version or a particular JRE family. Both selection of a specific JRE version, or any in a particular family, are supported in the new plug-in.
This guide describes how to develop an applet, the architecture of the Java Plug-in and best practices for applet development.