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. See the for information on these. More specifically you might want to check out the written by Stephen M Wynne (last updated january 2000 as of this writing). Another useful source of general information might be the maintained by Nathan Meyers. 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Please note that this FAQ is slightly out of date and is seeking an active maintainer. If you are willing to maintain it and are knowledgeable about Java in Debian, please contact the current maintainer. In any case, fixes to information that is not up to date are welcome (patches against the latest are even better).

In any case, if you want to send bugs on this FAQ please send them to the current maintainer. However, make sure you are reading the latest (english) version available at Note that translations, if available, might also be slightly out of date from the original, english, version. Check out the english version first if you are reading a translation before sending a bug. 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 /etc/jvm and /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 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 the 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. Blackdown's . 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 GNU/Linux 3.0 (Woody) 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 Notably Blackdown's port to Linux of Sun's Java Developer's Toolkit (SDK) or Java's Runtime Environment (JRE). Which you should retrieve from Blackdown, see . 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)?

There is the Kopi Java Compiler written in Java. And the super fast Jikes written in C++.

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?

Kaffe 1.0.5 is largely feature complete and now includes support for RMI. It is not clear as to whether Kaffe's serialization is "binary compatible" with Sun's implementation in all cases so there may be interoperation issues in some casses. Kaffe comes with a big class library.

libgcj (the run-time library for gcj) now includes an interpreter and ClassLoader.

tya, a JIT compiler, is also available. Is there a Java1 native compiler?

GCC, the Gnu Compiler Collection comes with GCJ, the Gnu Compiler for Java Java2 native compiler

It is unclear whether native compiler refers to the adaptive JIT capabilities in Java2 or to a compiler that understands Java2 semantics. In either case, Kaffe's JIT strategy is not adaptive but performs correctly, and improving, it is believed IBM's Jikes compiler understands Java2 concepts such as weak references. Does Debian have Java2 foundation libraries?

Many of these components have been cloned under a Free Software license. Kaffe provides many of these routines, including an up-to-date RMI implementation. There are, however, definitely shortcomings. Swing, as far as we know, has not been cloned. Is there a Java Debugger (jdb equivalent)?

jswat

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. Known problems

My version of jdb (jdb version 98/01/06) terminates after a program finishes execution, and I have to reset every breakpoint if I want to run through the program again. This makes using jdb extremely frustrating. Jdb also can't (easily) print the values in an array which is more than three elements long. Ddd lets me work around both of these annoyances.

ddd 3.1 and earlier would "hang" when receiving certain prompts with wierd thread names from jdb. This made it very hard to use ddd with jdb. This has been fixed in ddd 3.2. It doesn't look like ddd 3.2 has been packaged yet. I suspect the current packaged version of ddd won't work well with jdb. Is there an Appletviewer tool?

There are some alternatives for an appletviewer tool: Blackdown's appletviewer (in jdk1.1). Kaffe's appletviewer. Ibm's appletviewer (in ibm-jdk). Is there a Jar tool?

FastJar which is indeed very fast. Kaffe also has a jar tool. 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. Is there a full list of packages?

Below is a list given on packages that can be found in Debian 3.0 (aka Woody). The list does not display which of these packages can be found in main, and which is contrib or non-free. Runtime environments/Virtual Machines jdk1.1 (Sun's JDK 1.1.8) IBM 's JDK 1.1.8 (installer package) kaffe kissme sablevm Tools Compilers jikes (also jikes-1.14, jikes-gij, jikes-kaffe) jdk1.1 gcj tya (JIT compiler) Debuggers/Testing jswat junit IDE/Editors jedit jde Build tools ant jmk mmake Other fastjar jad (decompiler) Ant Libraries lib-dom-java lib-gnu.getopt-java lib-gnu.regexp-java lib-saxon-java libavalon-excalibur-java libavalon-framework-java libbcel-java libbsf-java libcrimson-java libcommons-beanutils-java libcommons-collections-java libcommons-digester-java libjdom-java libjunitperf-java libldap-java liblog4j liblogkit-java libnbio-java liboro-java libpgjava libreadline-java libregexp-java libservlet2.3-java libservlet2.2-java libsoap-java libtomcat4-java libxalan-java libxalan2-java libxerces-java libxerces2-java libxt-java Status of Java in Debian GNU/Linux 3.1 (Sarge) Are there many changes?

Yes, quite some. There have been very interesting developments in Debian Java lately. Slowly, there seem be developed a set of Debian tools to deal with maintaining Debian package of Java applications and libraries. 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.

In addition to this, ant has found its way into main, paving to way for other packages to enter main.

And the eclipse seems to get rather stable. Early August 2003, the gcj team even was able to compile the IDE to native code, using only minor modifications.

It is quite useful to first browse the section on Java in Debian GNU/Linux Woody (since those in woody are also in later releases, see ), but there are somes changes. Instead of listing all the packages again, this section will list only changes: eclipse An extensive IDE sablevm A free Virtual Machine free-java-sdk A free Java SDK (compiled from DSFG compliant Java tools) libgnome0-java Java bindings to Gnome GUI library gjdoc A Javadoc 1.3 replacement (90% of Doclet API implemented) kaffe Release 1.1.3 can run much more software than 1.0.5 in woody ant Version 1.6 is in main

The following packages are no longer in testing/unstable: libswing-java Which is mentioned here: . Status of Java in Debian GNU/Linux 4.0 (Etch)

The Etch release was the first one to provide Sun's JDK environment without the need to download it from third-party repositories (see ).

As part of the effort to move Java packages to main, 36 new Java packages were moved to main after being built with free Java development tools. Notably, ant (a Java-based build tool), libstruts1.2-java (a MVC framework), tomcat5 (a Java servlet engine) and eclipse (a developer's environment platform) have been moved to main. For the full list see the . Which Java package are currently in main?

At the time of writing, 209 Java packages were found in main, of which 119 were Java libraries. To see the list of packages in main (i.e., not contrib and non-free), try: grep-available -F Depends -sSection,Package java | paste -sd " \n" | \ grep -v contrib | grep -v non-free | sort

There are additional packages in the contrib section which can be found with a command similar as the one above.

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

An overview of packages that are still not in main is found at the Debian Wiki site: .

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. A number of packages have been moved to main and new releases of GNU Classpath, SableVM, and Kaffe promise further steps ahead. Two of the major issues currently being looked at are making gjdoc a proper javadoc replacement and building ant with Free Software only. People wanting to help can start by inspecting packages labeled as unknown on the 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)

The Lenny release was the first one to provide Sun's OpenJDK environment (see ).

A more up-to-date status of Java in the current Debian release is available at the . 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: Sun's jdk 1.4 (port made by Blackdown, see or go to ) kaffe. Sun's Java 5 jdk, available in the Debian 4.0 etch release in the non-free section. Sun's Java 6 jdk, available in Debian lenny (unreleased, currently testing) and Debian sid, also as packages in the non-free. Sun's OpenJDK 6 jdk, available since the Debian 5.0 lenny release in the main section.

Previous release of Debian included an installer package for IBM's Java Development Kit, but that is not longer available.

Since the Debian 3.1 'sarge' release, Debian provides the free-java-sdk package which makes up a free Java Software Development Kit (SDK). All software it depends on are DFSG compliant. 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: kaffe: . 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

If you are using the Debian 4.0 'etch' release you will find Java 5 instead. Similarly, you can install the Java development kit: apt-get install sun-java5-jdk or the Java 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 library 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 . Java 2 SE (aka JDK1.2)

Why is Sun's Java 2 SE (aka jdk 1.2) not available?

Due to license problems. Clause 2 of the (check also the ) that comes with is says: Software is confidential and copyrighted. Title to Software and all associated intellectual property rights is retained by Sun and/or its licensors. Except as specifically authorized in any Supplemental License Terms, you may not make copies of Software, other than a single copy of Software for archival purposes. What are the problems with Suns' new license?

Sun has moved to a new license the Sun Community License, like the GPL it is a viral license, but making all it touches subject to Sun licensing fee. The SCSL even goes so far as to define any implementation of a Sun specification as a "Modified Work". Basically, this means that if you implement any part of the new 1.2 API or Jini API, even from scratch, Sun will "own" your implementation and you will have to pay them for the right to use it. 13. "Modification(s)" means (i) any change to Covered Code; (ii) any new file or other representation of computer program statements that contains any portion of Covered Code; and/or (iii) any new Source Code implementing any portion of the Specifications. What is the SCSL?

The SCSL is the "Sun Community Software License" that can be found . It is not compatible with Free Software for several reasons, and agreeing to this license (e.g. by downloading source covered by the SCSL) will make it impossible for you to contribute to free software clean-room implementations. According to Sun, this includes using documentation and API specifications available only under SCSL.

To quote one open source developer, the SCSL is "about as free as the former Soviet Union".

However, if you have never agreed to the SCSL, then it is still permissible, barring any patents that Sun has for the technology, for you to create your own clean room version of the 1.2 API. It is important that you never agree to the license, even for the documentation. For example, if you buy a printed book which describes the API, there is a long legal history (in the US at least), that prohibits attaching these kinds of contracts to books. Can I use jdk1.2 while working with the free Java implementations?

Clause 1 of the Supplemental License Terms says: [You] 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;

Which seems to prevent one from making his own implementation of the standard Java classes using the JDK.

However, it is unclear whether or not the word `additional' includes reimplementations of existing classes, or whether it applies only to classes with new names. Why is (some) free software not implementing Java2?

Sun has made public statements in connection with their legal strategy in the Sun-Microsoft lawsuit that indicate that the company considers the published specifications of Java2 to be intellectual property that can not legally be used by persons involved in efforts to create Java2 clean-room implementations. For this reason, some open source projects have decided to not implement Java2 any time soon. One example is Kaffe. Some projects (like the Classpath project) have decided to challenge Sun's legal position and are going ahead with Java2. 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 or Blackdown 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.