Difference between revisions of "Java"

Revision as of 12:51, 28 September 2013

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"Java is a programming language originally developed by Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of computer architecture." — Wikipedia article

Installation

The only JVM implementation in supported repositories is the open source OpenJDK. Additional Java implementations are available via the AUR. Keep in mind that the open-source and closed-source versions cannot be installed simultaneously. The OpenJDK is nearly perfect, and it should not be necessary to install Oracle's proprietary version of Java.

OpenJDK JVM

Install the OpenJDK Java runtime environment (JRE) with the package jre7-openjdk, available in the official repositories. There is also a Java development kit (JDK) available with the package jdk7-openjdk.

If you want Java functionality in browsers (Java applets and Java Web Start), install icedtea-web-java7. For more details see Browser Plugins#Java (IcedTea).

Flagging OpenJDK packages as out-of-date

Please flag packages jre7-openjdk-headless, jre7-openjdk and jdk7-openjdk as out-of-date based on their IcedTea version (2.3.4) rather than on their Oracle version (u9). IcedTea-web project (package icedtea-web-java7) have version number that are independent from the IcedTea one (packages jre7-openjdk-headless, jre7-openjdk and jdk7-openjdk) so please flag each package based on its right version number.

Oracle JVM

The AUR contains the Oracle implementations of JRE and JDK: jre^AUR and jdk^AUR.

Oracle JVM 6

The AUR contains jre6^AUR and jdk6^AUR, which are the Oracle implementations of Java SE 6. If you want to use Java 6 alongside an up to date version (OpenJDK or Oracle), install jre6-compat^AUR and jdk6-compat^AUR.

Oracle JRockit JIT JVM (+JDK)

JRockit is a JIT version of Java, provided by Oracle and available as jrockit^AUR from the AUR.

VMkit LLVM-based JIT VM

VMkit is an LLVM-based framework for JIT virtual machines. J3 is a JVM running on VMkit. The webpage can be found here: [vmkit]. J3 depends on the GNU classpath libraries, but may also work with the Apache class path libraries.

Parrot VM

The Parrot VM offers experimental support for Java through two different methods: Either as a Java VM bytecode translator or as a Java compiler targeting the Parrot VM. parrot is available in the official repositories and parrot-git^AUR in the AUR.

Troubleshooting

MySQL

Due to the fact that the JDBC-drivers often use the port in the URL to establish a connection to the database, it is considered "remote" (i.e., MySQL does not listen to the port as per its default settings) despite the fact that they are possibly running on the same host, Thus, to use JDBC and MySQL you should enable remote access to MySQL, following instructions in MySQL article.

Java sound with Pulseaudio

By default, Java and Pulseaudio do not get along very well with each other, but this is easy to fix using padsp.

(These paths are correct for Sun's Java, you will need to change the paths for OpenJDK)

First, rename the java binary to java.bin

# mv /opt/java/jre/bin/java /opt/java/jre/bin/java.bin

Then, create a new launcher script at /opt/java/jre/bin/java

#!/bin/sh
padsp /opt/java/jre/bin/java.bin "$@"

Finally, make the launcher script executable

# chmod +x /opt/java/jre/bin/java

You will need to redo this process on each update of Java.

You can also try replacing padsp with aoss, which can also fix it under standard ALSA as well as in Pulse, do what works best. I must warn everyone that these hacks sometimes work perfect, but are sometimes very unstable as well.

Impersonate Another Window Manager

You may use the wmname from suckless.org to make the JVM believe you are running a different window manager. This may solve a rendering issue of Java GUIs occuring in window managers like Awesome or Dwm.

$ wmname LG3D

(You must restart the application in question after issuing the wmname command.)

This works because the JVM contains a hard-coded list of known non-re-parenting window managers. For maximum irony, many users prefer to impersonate “LG3D,” the non-re-parenting window manager written by Sun, in Java.

Fonts are Illegible

In addition to the suggestions mentioned below in #Better_font_rendering some fonts may still not be legible afterwards. If this is the case there is a good chance ms-fonts are being used. Install ttf-ms-fonts^AUR from the AUR.

Tips and tricks

Behavior of most Java applications can be controlled by supplying predefined variables to Java runtime. From this forum post, a way to do it consists of adding the following line in your ~/.bashrc (or /etc/profile.d/jre.sh to affect all users):

export _JAVA_OPTIONS="-D<option 1> -D<option 2>..."

For example, to use system anti-aliased fonts and make swing use the GTK look and feel:

export _JAVA_OPTIONS='-Dawt.useSystemAAFontSettings=on -Dswing.aatext=true -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel'

Better font rendering

Both closed source and open source implementations of Java are known to have improperly implemented anti-aliasing of fonts. This can be fixed with the following options: awt.useSystemAAFontSettings=on, swing.aatext=true

GTK LookAndFeel

If your Java programs look ugly, you may want to set up the default look and feel for the swing components: swing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel.

Some stubborn Java programs insist on using the cross platform Metal look and feel. In some of these cases you can force these apps to use the GTK look and feel by setting the following property:

swing.crossplatformlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel.

Symlinks change

Typically, OpenJDK installation creates symlinks in /usr/bin for java, javac ... etc. If you want to change these symlinks to any other JDK (e.g. if you installed environment-compat packages of Oracle JDK), this script might be handy for you.