Introduction to this FAQ

This FAQ was started by Javier Fernández-Sanguino who on February 1st, 2000 was (bold?) enough to send a message to the debian-java mailing list with the subject "How about a Debian-Java-FAQ?". Of course, since "every idea is a responsibility" he had to do this himself looking through the three month-long archive of the newborn mailing list.

The purpose of this FAQ is to be a place to look for all kinds of questions a developer or user might have regarding Java as far as Debian is concerned. It includes license issues, development packages available, and programs related to building a Free Software Java environment.

Thanks go to all the (many) contributors from the debian-java mailing list, who have made this document possible. Without their knowledge this FAQ would not be at all possible since I only have a vague knowledge of what they're talking about when I browse the list.

Special thanks go to Paul Reavis, whose previous Debian-JDK informational page I used to add more information, and who made useful suggestions to this document. Also to Peter Moulder who revised thoroughly the FAQ and provided many suggestions, to Juergen Kreileder, maintainer of Blackdown's debian packages who pointed out some mistakes, and to Egon Willighagen, who has provided quite a lot of proper patches to update its content.

This document does not address issues with other Linux distributions, or with non-Debian-specific problems. Location of this FAQ

This FAQ is published under the Debian Documentation Project at . The java-common (available at ) provides an HTML version for offline reading. The package version does not provide Text and PDF versions currently (if you want them please submit a bug 'wishlist' to the package). Also, the web version might be more up-to-date than the package's offline version. Sending bugs on this FAQ

Please note that this FAQ is still outdated but gets updated step by step.

Please file bug reports against the java-common package if you find errors or have suggestions on how to improve this document. However, make sure you have read the latest online version of the english text available at before filing a bug report. Translations, if available, and the offline version in the java-common package might be out of date. Complementary information

Users might want to access some online sources to complement the information available in this FAQ which might be, sometimes, too out of date. The main source of information is the at the Debian's wiki.

Since Ubuntu is based on Debian, some users might find it helpful to check the tips on on Ubuntu's wiki. Uncovered issues

This FAQ does not describe some issues due to lack of time and/or information. If you are able to help in any of these, please, provide them to the documentation maintainer: Information on how to use update-alternatives to handle Java and how to work with /etc/java. Information on how to setup a fully working Servlet engine (Application Server) using Apache and Tomcat or information on how to setup non-free application servers (such as WebSphere) in Debian. Specific information targeted for non-i386 users (PowerPC users and AMD64 users), some can be found in Ubuntu's wiki. Introduction to Java What is Java?

Java is a strongly-typed platform-independent object-oriented programming language often associated with the World Wide Web. Java was developed by (now Oracle) for embedded applications, but has since grown to become a general-purpose programming language. Java source code can either be compiled to a machine-independent byte-code that can be run by Java virtual machines, or it can be compiled directly to executable code for any number of platforms, including Linux, Win32, and others.

A common API, shipped with all Java development environments, provides socket support, a graphical user interface widget set, graphical drawing tools, standard IO, events, math, database interfaces, and multithreading, to name a few.

The multithreading support can happen either in kernel threads or userland threads, depending on the implementation of the Java virtual machine used.

Of course, Java is also the name of a popular island of Indonesia: check out the facts at . Why would I be interested in Java?

Java is widely used in large and small scale distributed, server, and client applications. It's fun to use. The javadoc tool creates documentation from comments in the code, so if you comment your code you get the docs for free. What is a JIT?

JIT is an acronym for Just In Time. It refers to a VM plugin to speed up VM execution by compiling bytecode to native machine code. Where can I read more about Java?

Of course, would be the first place to read information on Java, right from the company who started it (i.e. Sun). However good places for Java and Linux could be: Sun's pages. GNU's Enterprise in a Nutshell by Gary Meyer, at . Explains how to set up an environment including JDK, web server, Java servlets, JDBC access to a database and EJBs. If you are interested read also Java Enterprise in a Nutshell at . The , the following articles might be worth reading: Issue 105 Issue 94 Issue 66 and . The , the following articles might be useful: Issue 87 Issue 69 Issue 48 Issue 45 Issue 33 Issue 32 Issue 25 , a free multilingual journal: March 2003: January 1999: July 1998: The Java-CGI HOWTO from David H. Silber at explains how to set up your server to run Java CGIs. Maybe it is worth looking at servlets. Java Programming on Linux, by Nathan Meyers, website at , which is a book devoted to the topic of using Java on Linux (there's no online version of it, though) Other sites regarding Java would be: The Java Lobby . Brewing Java: a tutorial at . If you are browsing the web for free Java information you can of course use Google. If you are looking for applets with source code look at . Check also for pointers to the free Java platforms available, which might or might not be listed in GNU's webpages devoted to Java. Where can I ask questions about Java on Debian?

The appropriate place to ask such questions is debian-java at lists.debian.org. You can subscribe at the page. Status of Java in Debian's older releases (before Lenny) Is the information in this chapter still up to date?

Probably not but it takes some time to re-check every entry. That is why we keep the information for a while. Where is Debian Java going?

The first thing you should understand about the design strategy of Debian is that our goal is to produce a 100% Free Software platform. In that sense, some of the Java tools available are not available in the standard Debian distribution for licensing reasons, not for any technical motivation (see ).

That said, basically all of the technologies you might ask about can be or are available for Debian immediately. In order to usefully answer your questions, however, here you have a status from an Open Source availability perspective.

If you are really interested, read the following: and . This section is a summary of the information therein. (Note: this information might not be fully updated at this point in time, it was written around 1999) Is there a Java1 compiler (.java to .class)?

Gcj can also compile .java to .class. CVS version currently does handle inner classes, as well as any other jdk 1.1 constructs, but might not be able to compile a complicated program like the XSL processor xt. It is written in C, so is reasonably fast. It generates reasonably good bytecode. And of course being able to use the same compiler for .java to .class and .java to native has its advantages. Is there a Java1 JVM or JIT?

libgcj (the run-time library for gcj) now includes an interpreter and ClassLoader. Is there a Java1 native compiler?

GCC, the Gnu Compiler Collection comes with GCJ, the Gnu Compiler for Java Is there a Java Debugger (jdb equivalent)?

Gdb can debug native code produced by Gcj. Stuart Grossman (Cygnus) also wrote support for Gdb to debug other VMs using JVMDI. This has not been released, because the Gdb internals were changed at the same time, and no-one has had time to re-integrate the changes. We can probably get Cygnus to release the old code, if someone wants to look into getting this stuff working with the current Gdb internals. (A non-trivial job.)

See on how to debug gcj-compiled Java programs. What free edit-interactive/graphical debugging tools are available on Debian?

jde, ddd, more?

One of the some nice features of jde are autoindention and syntax highlighting, but it also supports debugging and compilation. Is there a Jar tool?

FastJar which is indeed very fast. Is there a Javadoc tool?

doc++ can work with C++ and Java. Additionally, there are the gjdoc and gjdoc-native packages. Does Debian do Enterprise Java Beans (EJB)?

There is activity in this area, the most noteworthy being the Open Source EJB implementation from Bull in France called Jonas. I have done some work with this system and it provides a good start towards a full EJB feature set. In particular, it provides a transaction monitor and a container based persistance implementation. I have used this system on Linux with free databases such as Postgresql. I have not been able to get the system fully operational on Kaffe. Additionally, the system depends on many Sun APIs which have not been cloned (JTA, JNDI, and EJB itself). What is JAIN?

It seems to be a system for controlling large scale, integrated communications infrastructures and modeling events with such networks via the JavaBeans API. The scale of this effort seems very large and encompasses the work of many organizations. The work is very new and seems to tie into Sun's SCSL strategy, which leads us me to believe that there is not much in the way of Open Source options in this area. However, some protocols such as H.323 are genuinely open and are even cloned so it is possible that chunks of the JAIN system may exist in a scattered manner. We have no knowledge of a serious Free Software implementation of RTP or the H.323 infrastructures in Java. What is Jini?

Jini presents an especially pronounced Free Software problem. Jini is only available as source from Sun and that source is only available under the SCSL. The SCSL is not compatible in any sense with either the legal mechanics or the political spirit of Free Software. The SCSL also makes cloning the API of an SCSL implementation illegal which precludes even a clean room replication of Jini. If you are interested in tuple space type implementations there are Open Source options. Are there many changes in Sarge?

At this moment, there only seems to be dh_javadoc, which is a tool in the gjdoc package. However, people spoke about other tools on the debian-java mailing list in 2003.

The Etch release was the first one to provide Sun's JDK environment without the need to download it from third-party repositories (see ). Which Java package are currently in main?

The website also maintains a list (probably more up to date) of java packages. What keeps Java packages out of main?

The current status, as of this writing (june 2004) is that there is progress of moving packages that use Java but can be run without the aid of non-free software from contrib to main. What can I expect in future releases?

In November 2006 Sun announced that Java would be open sourced under the GPL and provided source for the javac compiler and HotSpot virtual machine. Sun published their Java sources under the name OpenJDK. A small part, initially some 4% and by 2008 down to 1%, mainly in the Class library, is missing from the sources, because Sun does not hold the copyright themselves.

Debian has a roadmap to publish all of Sun's opensource Java technologies as described in the . The current version of the roadmap is at the . Status of Java in Debian GNU/Linux 5.0 (Lenny) What is new in Lenny?

The Lenny release was the first one to provide Sun's OpenJDK environment (see ). Lenny ships OpenJDK 6 with the IcedTea patches in version 1.1. Lenny updated GCJ to the new major version 4.3 and Ant to version 1.7. It provides Maven 2.0 but Maven cannot yet be used to build official Debian packages because it downloads random binaries from its central repository during build time. The java-common package provides new meta packages default-jdk and default-jre which declare dependencies to the appropriate gcj and gij packages. The new source package javatools contains useful helper tools for packaging Java software for Debian.

Thanks to the development that happened in gcj and classpath and thanks to the availability of openjdk many Java packages could be moved from contrib to main.

There are two new source packages glassfish and jbossas4 but they build only some core libraries and do not work as full JEE application servers yet. The main reason is that many free Java libraries are not yet packaged for Debian but are needed as (build) dependencies. But at least there is Hibernate 3 available in the contrib component. Status of Java in Debian Squeeze What is new in Squeeze?

The information in this chapter is probably out of date as Squeeze is not yet released and changes rapidly.

Squeeze ships with OpenJDK 6 and its IcedTea patches 1.8. The default ant version is 1.8 but there is a compatibility package with version 1.7. Java-common has switched to OpenJDK as the default-jdk on most architectures. Squeeze has updated GCJ to version 4.4. The new Debian Orbital Alignment Team has updated Eclipse to version 3.5.

Squeeze ships a fully working Tomcat 6 and Jetty 6 but both Glassfish and JBossAS 4 are still incomplete. Thanks to OpenJDK and the switch to OpenJDK as the default JDK even more Java packages in the contrib component (e.g. Hibernate 3) could be moved to main.

Maven has been updated to version 2.2 and it is accompanied by new helper packages: maven-repo-helper, maven-debian-helper, and several Maven plugins. It is now possible to build Debian packages with Maven because Debian has its own repository of POM files. What are the most important changes in the Java policy? The -gcj packages are now deprecated but we keep them if the are good reason. The virtual package java-virtual-machine is gone and package must not depend or recommend java-virtual-machine. Please check the policy for more details. Java Development

What full-fledged Java development platforms are available in Debian?

If you are looking for an integrated, java virtual machine, compiler and runtime environment Debian does provide them. Of course that would depend on the Debian GNU/Linux version you are using, generally speaking they would be: The deprecated Kaffe in Debian 5.0 Lenny. The deprecated Sun Java 5 jdk, available in the Debian 5.0 Lenny release in the non-free component. Sun's Java 6 jdk, available in Debian Lenny and Debian Squeeze, also as packages in the non-free component. Sun's OpenJDK 6 jdk, available since the Debian 5.0 Lenny release in the main section. The combination GCJ, GIJ, and Classpath in the main section.

It is recommended to install one of the default-jdk or default-jre meta packages which either installs OpenJDK or GCJ depending on the architecture and Debian version. What free platforms are there and how can I contribute?

Please help one of the Free Java implementations if you want to use Java in Debian. There are a lot of projects that you can choose from: gcj and libgcj: jikes: . A fast compiler written in C++ (check also ). (The new license seems to be finally really free) kopi: .Yet Another Free Java Compiler, this time written in Java, and GPL. Included in Kaffe since release 1.0.5. FastJar , as a jar tool. (this link seems to be broken, anyone?) Classpath or . Most of the Standard classes for Java 1.2 (except Swing and RMI) are implemented by the ClassPath project, it tries to build an alternative to jdk's 1.2 core classes. Most of the RMI classes are implemented by NinjaRMI Autoconf macros helps easy recompilation of Java programs. Mauve is a free suite to test if these tools are 'compliant'.

Most free Java development is grouped under the . There is a list on free Java at . Questions on platforms and license concerns Java 5 and 6

There are binary packages available for the Java 5 and Java 6 platforms since the Debian 5.0 ('lenny') release. These packages are available in the non-free section, so you have to configure your apt sources appropiately. If you have the following in your /etc/apt/sources.list: deb http://ftp.debian.org/debian etch main you need to change it to: deb http://ftp.debian.org/debian etch main contrib non-free Once this is done and you have updated your package database. You can either install the Java development kit: apt-get install sun-java6-jdk or the Java runtime environment: apt-get install sun-java6-jre

Similarly, you can install the Java 5 development kit: apt-get install sun-java5-jdk or the Java 5 runtime environment: apt-get install sun-java5-jre

Sun recommends you update the alternatives system to have Sun's tools as the default: update-java-alternatives -s java-6-sun Or for java 5: update-java-alternatives -s java-1.5.0-sun Sun's OpenJDK

Sun adopted in november 2006 the GPL license for almost all of the virtual machine and GPL v2 + the Classpath exceptionThis is similar to GCC linking exception in that it allows non-GPL code to be linked with the GPL code. This exception was developed by the for the class libraries and those parts of the virtual machine that expose public APIs.

As a consequence, the free OpenJDK code is available in Debian since the 5.0 (lenny) release.

You can install the Java development kit: apt-get install openjdk-6-jdk or the Java runtime environment: apt-get install openjdk-6-jre

For more information see . IBM's Developer Kit for Linux

Can Debian distribute IBM's jdk?

No, as its license does not allow redistribution. Actually, older releases (version 1.1) even restricted use of the jdk to specific distributions (and Debian was not included in the list).

You can still download it and use it in Debian yourself even Debian is not in the list of tested (or supported) platforms, see . Is it possible to obtain a licence for Debian?

It would still be non-free, because of item 8 in the : "License Must Not Be Specific to Debian". JRE

Can Debian distribute JRE?

(Quoted from Gene McCulley ) I don't think we can or want to distribute the JRE with Debian. The supplemental license terms of the JRE has a few very nasty clauses: 1. License to Distribute. You are granted a royalty-free right to reproduce and distribute the Software provided that you: (i)distribute the Software complete and unmodified, only as part of, and for the sole purpose of running, your Java applet or application ("Program") into which the Software is incorporated;

We might get away with this one since we distribute it together with Java applications bundled with Debian. But we also do want to allow people to download only the jre package. (ii) do not distribute additional software intended to replace any component(s) of the Software;

But we cannot agree to this one. We want to distribute Kaffe, Japhar, Classpath, Gcj, Kopi, Fastjar, etc which are intended to replace the JRE with a Free version. Even if we don't consider non-free part of Debian (the JRE would not go into main :) I think we should not encourage software that tries to prevent Free replacements. [...] (v) may not create, or authorize your licensees to create additional classes, interfaces, or subpackages that are contained in the "java" or "sun" packages or similar as specified by Sun in any class file naming convention;

My example why this is a bad clause was not so good since someone pointed out that you do not want to create something that is non standard. I do agree that we want a standard implementation of the core classes, but I also think that you should have the freedom to create non-standard classes. (Or fix bugs or stupid mistakes in the standard classes.) [...] and(vii) agree to indemnify, hold harmless, and defend Sun and its licensors from and against any claims or lawsuits, including attorneys' fees, that arise or result from the use or distribution of the Program.

And I don't think that Debian (or SPI) can or wants to do that.

So I am afraid that we also cannot distribute the Sun JRE. This isn't that bad since it is non-free software, but it is annoying. As I said before please help one of the (many) Free Java projects out there if you want to see a Free JVM, Standard Classes, Compiler, etc. in Debian. They are far from complete but they do work for most purposes GPL or LGPL?

Java uses dynamic linking at runtime. Using the reflection API and class loading, the linking can be completely data driven, specifying classes and methods by name. This moves the legal issues of using GPL'ed Java code into the user's hands, as a violation of the GPL can not be proven from the executable itself. Unlike plugins, Java classes do not even have to have a specific structure to be used in such ways. By using native methods and selecting DLL's at runtime, this problem might also affect native code.

Example: a GPL'ed Java dependency checker using the reflection API. Java's runtime linkage, in particular the reflection API, blurrs the lines between code and data even more than e.g. native plugins.

If you want to write Java code that can be used without the user having to worry about licensing issues, consider using the Lesser GPL (LPGL). If you want to avoid seeing your classes and packages being used by non-free software, consider using the GPL license.