Automatic javadoc subpackage generation

November 3, 2011 in fedora, java, macro, packaging, rpm

Do you hate repeating the same thing over and over again? I know I do…
Java packaging guidelines state that we have to include javadocs with all java packages. This means we have to repeat following code in almost all packages (except pom and resource projects):

...
%package javadoc
Summary: API documentation for %{name}
Group: Documentation
Requires: jpackage-utils

%description javadoc
%{summary}.
...

%install
...
# javadoc
install -d -m 755 %{buildroot}%{_javadocdir}/%{name}
cp -pr target/site/apidocs/* %{buildroot}%{_javadocdir}/%{name}

...

%files javadoc
%doc LICENSE
%doc %{_javadocdir}/%{name}
...
The code is practically the same in all packages so why not automate this? Well there were two main reasons why this wasn’t done before:
  • Copying of files needs to be done during install phase
  • If package contains license, javadoc has to have it too

We solved both of these in a fairly reasonable way. Resulting macro help looks like this:


# %create_javadoc_subpackage can be used to completely create
# javadoc subpackage for java projects.
# !!! Needs to be used at the end of %install section
# There are these variables that change its behaviour:
#
# %__javadoc_license - set if the license is in non-standard place to
# prevent Requires on main package
# %__apidocs_dir - set custom path to directory with javadocs
# (defaults to target/site/apidocs)
# %__javadoc_skip_requires - if defined javadoc subpackage will not
# require main package under any circumstances (useful
# if upstream doesn't provide separate license file)
#

Is it understandable enough? If you need to generate javadocs, just make them build and then add %create_javadoc_subpackage macro call at the end of %install section. Normally you shouldn’t have to change anything. We search in a few standard places for licenses. More specifically we look for LICENSE* COPYING* doc/LICENSE* doc/COPYING* license*. Do you have more ideas where to look? It’s easy to add. If we don’t find license we automatically add requires on main package and assume you put license in there. If upstream doesn’t provide separate license file you can do %global __javadoc_skip_requires t and we will ignore licensing completely.

I’d like this added to our packaging guidelines so we can start using it. My testing shows it works fairly well. I’d love to improve it so you could place it anywhere in the spec, not just %install section, but rpm macros are…complicated.
*Note*: For gory details head over to our git repository. For now it’s in separate feature branch.

Getting your Java Application in Linux: Guide for Developers (Part 2)

April 20, 2011 in fedora, howto, java, packaging

Ant and Maven

Last time I have written about general rules of engagement for Java developers if they want to make lives of packagers easier. Today I’ll focus on specifics of two main build systems in use today: Ant and Maven, but more so on Maven for reasons I’ll state in a while.

Ant

Ant is (or at least used to be) most widely deployed build system in Java ecosystem. There are probably multiple reasons for it, but generally it’s because Ant is relatively simple. In *NIX world Ant is equivalent of pure make (and build.xml of Makefile). build.xml is just that: an XML, and it has additional extensions to simplify common tasks (calling javac, javadoc, etc.). So the question is:

I am starting a new java project. How can I use Ant properly to make life easier for you?

The most simple answer? DON’T! It might seem harsh and ignorant of bigger picture and it probably is. But I believe it’s also true that Ant is generally harder to package than Maven. Ant build.xml files are almost always unique pieces of art in themselves and as such can be a pain to package. I am always reminded of following quote when I have to dig through some smart build.xml system:

Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.

  –Brian Kernighan

And I have a feeling some people try to be really clever when writing their build.xml files. That said, I understand there are times when using Ant is just too tempting so I’ll include a few tips for it anyway.

Use apache-ivy extension for dependencies

One of main problem with and is handling of various dependencies. Usually, they are in some subdirectory of main tree, some jars versioned, some not, some patched without any note about it…in other words nightmare in itself. Apache-ivy extension helps here because it works with dependency metadata that packagers can use to figure out real build dependencies including versions. We can also be sure that no dependencies are patched in one way or the other.

Ivy is nice for developers as well. It will make your source tarballs much smaller (You do have source tarballs right?!) and your build.xml nicer. I won’t include any examples here because I believe that Ivy documentation is indeed very good.

One lib/ to rule them all

In case you really don’t want to use Ivy, make sure you place all your dependencies in one directory in top level of your project (don’t scatter your dependencies, even if you are using multiple sub-projects). This directory should ideally be called lib/. It should contain your dependencies named as ${name}-${version}.jar. Most of the time you should include license files for every dependency you bundle, because you are becoming distributors and for most licenses this means you have to provide full text of the license. For licenses use identical name as jar filenames, but use “.license” suffix. All in all, make it easy to figure out your build dependencies and play with them.

Don’t be too clever

I can’t stress this enough. Try to keep your build.xml files to the bare minimum. Understanding ten 30 KiB big build.xml files with multiple-phase build and tests spread through 10 directories is no fun. Please think of poor packager when you write your build.xml files. I don’t mind having grey hair that much, but I’d rather if it came later rather than sooner.

Maven

And now we are coming to my favourite part. Maven is a build and project management tool that has extensive plugin support able to do almost anything developer might ask for. And all that while providing formal project structure, so that once you learn how Maven works in one project you can re-use your knowledge in other projects.

Maven goodies

Maven provides several good things for packagers such as providing clear dependencies and preventing simple patched dependencies from sneaking in. Most important advantage for packagers coming with Maven is the fact that problems are the same in all projects. Once you understand how certain Maven plugin works, you will know what to expect and what to look for. But Maven is nice not just for packagers, but also for developers.

Declarative instead of descriptive

You don’t tell Maven:

Add jar A, jar B to the classpath, then use this properies file to set-up test resources. Then compile tests (Have you compiled sources yet?) and then … and run them with X

Instead you place test files and resources into appropriate directories and Maven will take care of everything. You just need to specify your test dependencies in nice and tidy pom.xml.

Project metadata in one place

With Maven you have all project information in one place:

  • Developer contact information
  • Homepage
  • SCM URLs
  • Mailinglists
  • Issue tracker URL
  • Project reports/site generation
  • Dependencies
  • Ability modify behaviour according to architecture, OS or other property

Need I say more? Fill it out, keep it up-to-date and we will all be happy.

Great integration with other tools

Ecosystem around Maven has been growing in past years and now you will find good support for handling your pom.xml files in any major java IDE. But that is just the tip of the iceberg. There are Maven plugins adding all kinds of additional tool support. Running checkstyle on your code, helping with licensing, integration with gpg, ssh, jflex and making releases. There are plugins for that and more.

Support for Ant

If you are in process of migrating your build system from Ant to Maven, you can do it in phases. For parts of your builds you can easily run Ant with maven-ant-plugin. Good example of such migration in progress is checkstyle. In version 5.2 they introduced Maven build system while preserving their old layout and running Ant for tests.

Maven messier side

A.K.A What you need to be aware of. It’s generally quite hard to do something bad in Maven, because it won’t let you do that easily. That said, there are plugins that can make it hard for us to package your software.

maven-dependency-plugin:copy-dependencies

This specific goal can potentially cause problems because it allows to copy classes from dependencies into resulting jar files. As I wrote last time, this is unacceptable because it creates possible licensing, security and maintenance nightmares. If you need even just one class from another project, rather than copying it, add it as a dependency into pom.xml

maven-shade-plugin

Shade plugin is a very shady plugin (pun intended). It can be used to weave depdencies inside your jars while changing their package names and doing all kinds of modifications in the process. I’ll give you a small test now :-) Let’s say you have jar file with following contents:


META-INF/
META-INF/MANIFEST.MF
META-INF/maven/
META-INF/maven/org.packager/
META-INF/maven/org.packager/Pack/
META-INF/maven/org.packager/Pack/pom.properties
META-INF/maven/org.packager/Pack/pom.xml
org/
org/packager/
org/packager/signature/
org/packager/signature/SignatureReader.class
org/packager/signature/SignatureVisitor.class
org/packager/signature/SignatureWriter.class
org/packager/Pack.class

Can you tell, from looking at jar contents where is org.packager.signature subpackage coming from? Take your time, think about it. Nothing? Well here’s a hint:



org.apache.maven.plugins
maven-shade-plugin



org.objectweb.asm
org.packager




I believe this demonstrates why usage of shade plugin is evil (in 99% of cases at least). This is especially problematic if the shaded packages are part of public API of your project, because we won’t be able to simply fix this in one package, but it will cascade up the dependency chain.

maven-bundle-plugin

Bundle is one of the more controversial plugins, because it can be used both for good and bad :-) One of the most important good use cases for bundle plugin is generating OSGI bundles. Every project can easily make their jar files OSGI compatible by doing something like this:


...
bundle
...



org.apache.felix
maven-bundle-plugin
true



...

Easy right? Now to the darker side of bundle plugin. I have another example to test your skills. This one should be easier than shade plugin:


META-INF/MANIFEST.MF
META-INF/
META-INF/maven/
META-INF/maven/org.packager/
META-INF/maven/org.packager/Pack/
META-INF/maven/org.packager/Pack/pom.properties
META-INF/maven/org.packager/Pack/pom.xml
org/
org/objectweb/
org/objectweb/asm/
org/objectweb/asm/signature/
org/objectweb/asm/signature/SignatureReader.class
org/objectweb/asm/signature/SignatureVisitor.class
org/objectweb/asm/signature/SignatureWriter.class
org/packager/
org/packager/Pack.class

Problem is the same as with shade plugin (bundling of dependencies), but at least here it’s more visible in the contents of the jar and it will not poison API of the jar. Just for the record, this is how it was created:



org.apache.felix
maven-bundle-plugin
true


org.objectweb.asm.signature



Summary

Today I wrote about:

  • Ant and why you shouldn’t use it (that much)
  • Ant and how to use it if you have to
  • Maven and why it rocks for packagers and developers
  • Maven and its plugins and why they suck for packagers sometimes

There are a lot more things that can cause problems, but these are the most obvious and easily fixed. I’ll try to gather more information about things we (packagers) can do to help you (developers) a bit more and perhaps include one final part for this guide.

Getting your Java Application in Linux: Guide for Developers (Part 1)

April 8, 2011 in fedora, howto, java, packaging

Introduction to packaging Java

Packaging Java libraries and applications in Fedora has been my daily bread for almost a year now. I realized now is the time to share some of my thoughts on the matter and perhaps share a few ideas that upstream developers might find useful when dealing with Linux distributions.

This endeavour is going to be split into several posts, because there are more sub-topics I want to write about. Most of this is going to be based on my talk I did @ FOSDEM 2011. Originally I was hoping to just post the video, but it seems to be taking more time than I expected :-)

If you are not entirely familiar with status of Java on Linux systems it would be a good idea to first read a great article by Thierry Carrez called The real problem with Java in Linux distros. A short quote from that blog:

The problem is that Java open source upstream projects do not really release code. Their main artifact is a complete binary distribution, a bundle including their compiled code and a set of third-party libraries they rely on.

There is no simple solution and my suggestions are only mid-term workarounds and ways to make each other’s (upstream ↔ downstream) lives easier. Sometimes I am quite terse in suggestions, but if need be I’ll expand them later on.

Part 1: General rules of engagement

Today I am going to focus on general rules that apply to all Java projects wishing to be packaged in Linux distributions:

  • Making source releases
  • Handling Dependencies
  • Bugfix releases

For full understanding a short summary of general requirements for packages to be added to most Linux distributions:

  • All packages have to be built from source
  • No bundled dependencies used for building/running
  • Have single version of each library that all packages use

There are a lot of reasons for these rules and they have been flogged to death multiple times in various places. It mostly boils down to severe maintenance and security problems when these rules are not followed.

Making source releases

As I mentioned previously most Linux distributions rebuild packages from source even when there is an upstream release that is binary compatible. To do this we need sources obviously :-) Unfortunately quite a few (mostly Maven) projects don’t do source release tarballs. Some projects provide source releases without build scripts (build.xml or pom.xml files). Most notable examples are Apache Maven plugins. For each and every update of one of these plugins we have to checkout the source from upstream repository and generate the tarball ourselves.
All projects using Maven build system can simply make packagers’ lives easier by having following snippet in their pom.xml files:




...

maven-assembly-plugin


project




make-assembly
package

single




...


This will create -project.zip/tar.gz files containing all the files needed to rebuild package from source. I have no real advice for projects using Ant for now, but I’ll summarise them next time.

Handling dependencies

I have a feeling that most Java projects don’t spend too much time thinking about dependencies. This should change so here are a few things to think about when adding new dependencies to your project.

Verify if the dependency isn’t provided by JVM

Often packages contain unnecessary dependencies that are provided by all recent JVMs. Think twice if you really need another XML parser.

Try to pick dependencies from major projects

Major projects (apache-commons libraries, eclipse, etc.) are much more likely to be packaged and supported properly in Linux distributions. If you use some unknown small library packagers will have to package that first and this can sometimes lead to such frustrating dependency chains they will give up before packaging your software.

Do NOT patch your dependencies

Sometimes a project A does almost exactly what you want, but not quite…So you patch it and ship it with your project B as a dependency. This will cause problems for Linux distributions because you basically forked the original project A. What you should do instead is work with the developers of project A to add features you need or fix those pesky bugs.

Bugfix releases

Every software project has bugs, so sooner or later you will have to do a bugfix release. As always there are certain rules you should try to uphold when doing bugfix releases.

Use correct version numbers

This depends on your versioning scheme. I’ll assume you are using standard X.Y.Z versions for your releases. Changes in Z are smallest released changes of your project. They should mostly contain only bugfixes and unobtrusive and simple feature additions if necessary. If you want to add bigger features you should change Y part of the version.

Backward compatible

Bugfix releases have to be backwards compatible at all times. No API changes are allowed.

No changes in dependencies

You should not change dependencies or add new ones in bugfix releases. Even updating dependency to a new version can cause massive recursive need for updates or new dependencies. The only time it’s acceptable to change/add dependency version in bugfix release is when new dependency is required to fix the bug.

An excellent example of how NOT to do things was Apache Maven update from 3.0 to 3.0.1. This update changed requirements from Aether 1.7 to Aether 1.8. Aether 1.8 had new dependency on async-http-client. Async-http-client depends on netty, jetty 7.x and more libraries. So what should have been simple bugfix update turned into need for major update of 1 package and 2 new package additions. If this update contained security fixes it would cause serious problems to resolve in timely manner.

Summary

  • Create source releases containing build scripts
  • Think about your dependencies carefully
  • Handle micro releases gracefully

Next time I’ll look into some Ant and Maven specifics that are causing problems for packagers and how to resolve them in your projects.

Picasa Album Downloader roadmap

August 19, 2008 in en, google, java, projects, python

In my first post about Picasa Album Downloader java applet I promised more in-depth technical information about the project.

Project idea came when few of my less computer savvy friends wanted to download all photos from my Picasa Web Album. So far there have been few different ways to do that:

  • install Picasa and use it,
  • install some other software to download photos,
  • go photo-by-photo and download them one-by-one.

None of those methods is very user friendly. Why isn’t there a “Download album as zip archive” link on Picasa? I have a few theories, but that’s probably for another blog post :)

Question is: How to enable users to download Picasa albums easily? Apparently I was not the only one with the idea of creating web service to create zip file for users to download. Fortunately Google provides APIs for most of its services in few languages. More precisely you can access Picasa easily using:

  • .NET
  • Java
  • PHP
  • Python

Since I started learning Python step-by-step few months ago, I thought about using it for the job. Then I realized that I will need hosting for the web service. There are not too many free python hosting services. Those that are free usually have some restrictions.

Even Google provides hosting services using its own App Engine, with support for Python in particular. I created simple prototype python script that was able to download selected album from given user to the chosen output directory. It ran just fine when I was testing it, but stopped working when run inside dev_appserver.py. Reason? Hotlinking.

Picasa Web Album checks referer header and if it doesn’t match one of Google domains, Picasa blocks access to the images. Since App Engine dosn’t allow clearing of referer header, this effectively blocks using full scale images from Picasa in App Engine. So python is out. What else is there?

I don’t have much experience with .NET, and I also don’t think that it would be suitable for web application that is supposed to be free. I already had some experience with PHP and for project like this one, it would probably do the job just fine. There was a problem though…Google Data APIs needs at least PHP 5.14 to work, but hosting services I had at my disposal had lower versions installed.

Status? Python, .NET, PHP, Java. And here we are. The result is a Java applet that enables users to download full Picasa album without installing any software. There is also a project page at Google Code. First version took about 1 day to code. I released it under GPLv3, so if you want to contribute, you are welcome to do so. If you find any bugs or have ideas how to make the applet better, let me know.

Picasa Album Download

August 14, 2008 in en, google, java, projects, python

Picasa web albums is a great service. As far as I can tell it has very few disadvantages over competing websites. Although I have never used Flickr or similar services so I am not really one to judge.

There is one thing with Picasa web albums that quite a few people have asked me:

Can I download whole album from Picasa at once, without having to click through all the photos one-by-one?

Well I used to tell people to install Picasa to their computer, but less tech-savvy users had problems with this approach. Some companies also have restrictions on installing software in their networks. No wonder with numbers of trojans, malware and similar things on the Internet these days. Getting rid of them can take forever…

I found quite a few projects dealing with downloading from picasa. All of them required installing some application (or at least download one). Perfect solution? Web service.

As an aspiring Software engineer (pun intended) I set up on a quest to solve this problem once and for all. Goal:

  • Download complete Picasa Web Album into computer without having to install anything first
  • Multiplatform (Windows, Linux, MacOS X,…) support. Ideally only browser-requiring solution.

Simple right? Well yes and no. I will publish technical details and solutions I tried in some other post (edit: I already did). Now. without further ado, I present to you: