Hack 97 Run Native Java Applications

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Until recently, running Java applications on FreeBSD meant using the Linux compatibility mode.

Linux programs can sometimes be problematic on FreeBSD. Java© uses threading very heavily, and that's probably the poorest-emulated part of Linux binary compatibility. Some Java applications or class libraries just don't work correctly under Linux emulation. Native versions of the Java distribution had restrictive licenses, and it required a great deal of work to download and compile them. Fortunately, the FreeBSD Foundation has negotiated a FreeBSD Java license with Sun Microsystems. This hack demonstrates how to configure the FreeBSD version of Java.

What about native Java on NetBSD or OpenBSD? At the time of writing, neither system had a native Java port. You can run Java on a Linux emulator or via Tomcat.

9.10.1 Choosing Which Java Port to Install

The first requirement for running Java applications is a Java Virtual Machine (JVM) and the associated runtime support libraries. There are several Java Runtime Environments (JREs) or Java Development Kits (JDKs) available in ports.

A JRE contains everything necessary for an end user to run Java applications. A JDK contains all that, plus various extra bits required for developing, compiling, and debugging Java code.

The main criteria for choosing a port are:

  • Which version of Java do you need?

  • Do you want to run FreeBSD native code or Linux code run under emulation?

  • Do you prefer to run a precompiled binary or compile it yourself from source code?

Unless you have a specific requirement for an earlier version, choose the latest stable release, which, as of this writing, is Java 1.4.2. The native version, found in /usr/ports/java/jdk14, will give you the best performance, but you will have to compile it yourself. That is more easily said than done: compiling the JDK requires a great deal of disk space and CPU power, as well as a working copy of the 1.4.2 JDK. The first time you compile, you will have to install one of the Linux JDKs, such as the recommended /usr/ports/java/linux-sun-jdk14, but once you have a working native JDK, you can use it to compile any updates and uninstall the Linux version.

You can install several Java versions simultaneously without them interfering with each other. Each will install into its own subdirectory of /usr/local.

If you need a precompiled native version, choose one of the Diablo Java 1.3.1 ports. These use the same code base as the /usr/ports/java/jdk13 port, and they're certified, licensed, and released through the sponsorship provided by the FreeBSD Foundation (http://www.freebsdfoundation.org/downloads/java.shtml).

Diablo JDK 1.4 and JRE 1.4 versions are under development, but not yet available.

The Diablo Java packages are standard FreeBSD packages, so you can install them via pkd_add. However, you're better off installing from the Diablo ports, as that will provide you with the correct dependencies.

For example, to install the Latte Diablo JRE 1.3.1 port, visit http://www.freebsdfoundation.org/cgi-bin/download.cgi?package=diablo-jre-1.3.1-0.tar.bz2. Read and accept the license terms, and save the downloaded file as /usr/ports/distfiles/diablo-jre-1.3.1-0.tar.bz2. Then:

# cd /usr/ports/java/diablo-jre13 # make install

9.10.2 Running Java Applications

Starting up any Java application means running a Java Virtual Machine, which in turn loads a named Java class. That class is the entry point for the program. The JVM always requires the CLASSPATH environment variable to contain a list of .jar archives that store all of the Java classes required by the application. You can provide extra arguments to the JVM to limit its use of memory or other system resources, for example and the application itself may take further command-line arguments.

9.10.3 Standalone Java Applications

Many Java applications provide a shell script to set up the environment and to execute the JVM with the appropriate arguments. A typical example is ant (see /usr/ports/devel/apache-ant), the Java equivalent to make.

The installation process edits the script that will become /usr/local/bin/ant to use the Java version used when building the port. However, you can override the default Java version within the script by setting the JAVA_HOME environment variable:

% setenv JAVA_HOME=/usr/local/jdk14

9.10.4 Javavmwrapper

Given the wide variety of JVMs available under FreeBSD, adding code to all Java application wrapper scripts or otherwise configuring standalone Java applications to use the correct JVM could become a maintenance nightmare. Fortunately, the /usr/ports/java/javawmwrapper port provides the /usr/local/bin/javavm script, which all applications can run to discover the site's default JVM. javavm's configuration file, /usr/local/etc/javavms, contains a list of installed JVMs in the order of their preference. Installing or removing a JVM through ports will modify this file. You can also edit it by hand.

9.10.5 Applets

In the case of a Java applet, the web browser starts the JVM and downloads and runs the applet from the Web. Applets run in a special sandbox that denies them access to most of the local system, except for the browser window.

Java support in web browsers derived from Netscape (including Mozilla, Firebird, and Galeon) uses a plug-in that comes standard with the JDK. For the native JDK 1.4.2, the plug-in is /usr/local/jdk1.4.2/jre/plugin/i386/ns610/libjavaplugin_oji.so. To make this plug-in available to web browsers, create a symlink to this file from /usr/X11R6/lib/browser_plugins:

# cd /usr/X11R6/lib/browser_plugins # ln -s /usr/local/jdk1.4.2/jre/plugin/i386/ns610/libjavaplugin_oji.so .

Launch a web browser and type about:plugins into the location bar. You should see an entry for the "Java(TM) Plug-in," which claims to handle about 30 MIME types, all variants on application/x-java-something.

If you're using a Linux web browser under emulation, install the plug-in from one of the Linux Java versions.

9.10.6 Servlets

A servlet is all or part of a web application written in Java. It runs through a servlet container application, which abstracts out all of the common server-side functionality. Tomcat (/usr/ports/www/jakarta-tomcat41) and Jetty (/usr/ports/www/jetty) are two examples of these applications.

The servlet container application runs in much the same way as standalone Java applications.

9.10.7 Java WebStart

WebStart is a web-based mechanism for downloading and updating Java applications. Use the Preferences menu item in javaws to control the JVM that will run the WebStart-ed applications. Unlike applets, the downloaded applications run independently of the web browser. You don't need to download them again each time they run. They also have full access to the underlying system. The javaws application is a standard part of Java 1.4 or above. It lives in ${JAVA_HOME}/jre/javaws/javaws.

9.10.8 See Also

  • FreeBSD Foundation's Java downloads (http://www.freebsdfoundation.org/downloads/java.shtml)

BSD Hacks
BSD Hacks
ISBN: 0596006799
EAN: 2147483647
Year: 2006
Pages: 160
Authors: Lavigne

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