Java - ParabolaWiki

# Java

"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

Parabola GNU/Linux-libre officially supports the free OpenJDK versions 7 and 8. All these JVM can be installed without conflict and switched between using helper script parabola-java.

## Installation

The following packages are available in the official repositories:

OpenJDK 7:

Package name | Use
--- | ---
jre7-openjdk-headless | Java runtime environment (JRE) without any graphical tool - version 7
jre7-openjdk | Complete Java Runtime Environment (JRE) - version 7
jdk7-openjdk | Java Development Kit (JDK) - version 7
openjdk7-doc | OpenJDK javadoc - version 7
openjdk7-src | OpenJDK sources - version 7

OpenJDK 8:

Package name | Use
--- | ---
jre8-openjdk-headless | Java runtime environment (JRE) without any graphical tool - version 8
jre8-openjdk | Complete Java Runtime Environment (JRE) - version 8
jdk8-openjdk | Java Development Kit (JDK) - version 8
openjdk8-doc | OpenJDK javadoc - version 8
openjdk8-src | OpenJDK sources - version 8

Note: Installing a JDK will automatically pull its JRE dependency.
Note: After installation, the Java environment will need to be recognized by the shell ($PATH variable). This can be done by sourcing /etc/profile from the command line or by logging out/in again of a Desktop Environment.

Two common packages named java-runtime-common and java-environment-common are automatically pulled as dependency and provide environment file /etc/profile.d/jre.sh. This file contains all JVM common environment variables. Package java-runtime-common also provides a utility script parabola-java that can display and change the default Java environment. This script sets links /usr/lib/jvm/default and /usr/lib/jvm/default-runtime to point at a valid non-conflicting Java environment installed and Java runtime in /var/lib/jvm/java-${JAVA_MAJOR_VERSION}-${VENDOR_NAME}. Most executable provided by the Java environment set have direct links from /usr/bin, others are available in $PATH.

Warning: File /etc/profile.d/jdk.sh is not provided anymore by any package.

## Switching between JVM

Helper script parabola-java provides such functionalities:

    parabola-java <COMMAND>

    COMMAND:
    	status		List installed Java environments and enabled one
    	get		Return the short name of the Java environment set as default
    	set <JAVA_ENV>	Force <JAVA_ENV> as default
    	unset		Unset current default Java environment
    	fix		Fix an invalid/broken default Java environment configuration

### List compatible Java environments installed

    % parabola-java status

Example:

    % parabola-java status
    Available Java environments:
      java-7-openjdk (default)
      java-8-openjdk/jre

Note the (default) denoting that java-7-openjdk is currently set as default. Invocation of java and other binaries will rely on this Java install. Also note on the previous output that only the JRE part of OpenJDK 8 is installed here.

### Change default Java environment

    # parabola-java set <JAVA_ENV_NAME>

Example:

    # parabola-java set java-8-openjdk/jre

Note that parabola-java will not let you set an invalid Java environment. In the previous example, jre8-openjdk is installed but jdk8-openjdk is not so trying to set java-8-openjdk will fail:

    # parabola-java set java-8-openjdk
    '/usr/lib/jvm/java-8-openjdk' is not a valid Java environment path

### Unsetting the default Java environment

There should be no need to unset a Java environment as packages providing them should take care of this. Still should you want to do so, just use command unset:

    # parabola-java unset

### Fixing the default Java environment

If /usr/bin links are incorrect or if an invalid Java environment link is set, calling the parabola-java fix command tries to fix these. Also note that if no default Java environment is set, this will look for valid ones and try to set it for you. Officially supported packages "OpenJDK 7" and "OpenJDK 8" will be considered first in this order, then un-official packages from pcr repo.

    # parabola-java fix

### Former "One time setup" trick

Formerly, package java-common could be forced into using a Java installation by setting environment variable JAVA_HOME. This cannot be done anymore with latest version of java-runtime-common.

## Package pre-requisites to support parabola-java

This section is targeted at packager willing to provide packages in pcr repo for an alternate JVM and be able to integrate with Parabola JVM scheme to use parabola-java. To do so, packages should:

- Place all files under /usr/lib/jvm/java-${JAVA_MAJOR_VERSION}-${VENDOR_NAME}
- Ensure all executables for which java-runtime-common and java-environment-common provide links are available in the corresponding package
- Ship links from /usr/bin to executables, only if these links do not already belong to java-runtime-common and java-environment-common
- Suffix man pages with -${VENDOR_NAME}${JAVA_MAJOR_VERSION} to prevent conflicts (see jre8-openjdk file list where man pages are suffixed with -openjdk8)
- Do not declare any conflicts nor replaces with other JDKs, java-runtime, java-runtime-headless nor java-environment
- Use script parabola-java in install functions to set the Java environment as default if no other valid Java environment is already set (ie: package should not force install as default). See officially supported Java environment package sources for examples

Also please note that:

- Packages that need any Java environment should declare dependency on java-runtime, java-runtime-headless or java-environment as usual
- Packages that need a specific Java vendor should declare dependency on the corresponding package
- OpenJDK packages now declare provides="java-runtime-openjdk=${pkgver}" etc. This enables a third-party package to declare dependency on an OpenJDK without specifying a version

## 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 the instructions in MySQL#Grant Remote Access.

### 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 occurring 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, some users prefer to impersonate LG3D, the non-re-parenting window manager written by Sun, in Java.

### Missing text in some applications

If some applications are completely missing texts it may help to use the options under #Tips and tricks as suggested on this report made on Arch.

### Too many levels of symbolic links

If you get an error like:

    /usr/bin/java: line 2: /usr/lib/jvm/default/bin/java: Too many levels of symbolic links
    /usr/bin/java: line 2: exec: /usr/lib/jvm/default/bin/java: cannot execute: Too many levels of symbolic links

#Fixing the default Java environment should solve the problem. See also [1].

## Tips and tricks

Note: Suggestions in this section are applicable to all applications, using explicitly installed (external) Java runtime. Some applications are bundled with own (private) runtime or use own mechanics for GUI, font rendering, etc., so none of written below is guaranteed to work.

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 programs that are not run by sourcing ~/.bashrc, e.g., launching a program from Gnome's Applications view):

    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

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.

## Acknowledgement

This wiki article is based on ArchWiki. We may have removed non-FSDG bits from it.
Category:

- Programming language