Javahelper Tutorial

# Packaging Java with Javatools

Javatools replaces the existing jarwrapper package and also contains programs to help packagers in creating packages for Java programs and libraries.

## Packaging tools

The javahelper package consists of several small programs which make packaging Java programs and libraries easier. They are generally designed to work in the same fashion as the debhelper programs, but start with the `jh_` prefix.

All of the programs have their command line arguments documented in manpages.

## jh_build

Many Java programs and libraries are distributed without sane build systems. `jh_build` provides a simple interface for building Java source code into Jars, including setting the appropriate entries in the manifest.

In almost all cases all that needs to be done to call `jh_build` is to set `JAVA_HOME` and `CLASSPATH` and then call `jh_build` with the name of the jar and the directory containing the source.

    JAVA_HOME=/usr/lib/jvm/default-java
    CLASSPATH=/usr/share/java/esd.jar:/usr/share/java/jsch.jar
    jh_build weirdx.jar src

This command will compile all the Java files under src, set the classpath in the manifest and build it all into weirdx.jar.

A couple of other options are worth mentioning. If this jar contains an application rather than a library then the -m or --main option can be used to set the Main-Class attribute in the manifest which will allow the resulting jar file to be be executed

Alternatively, you may provide a debian/javabuild file containing one jar per line, each jar name followed by a list of source files or directories. In this case you can call `jh_build` with no jar or source and it will build those jars. The jars will then be removed by `jh_build --clean`.

`jh_build` also provides a --clean parameter which should be called in the clean target of debian/rules. It is called for you by `jh_clean`

`jh_build` will also create javadoc, but only for the last jar built in each package. It can be installed automatically using `jh_installjavadoc` (see below).

## jh_installlibs

For library packages Debian Java policy currently requires that the libraries be installed to /usr/share/java in a versioned format and with an unversioned symlink. `jh_installlibs` will take a jar and correctly install it.

As with debhelper programs, this can either take a jar as a parameter, or read a list of jars from a file in the Debian directory. It also follows the -p, -i and -a semantics of debhelper for selecting which packages to install the jar to. When operating on a package, `jh_installlibs` will read the list of library jars from debian/package.jlibs or debian/jlibs.

The jlibs file is a list of jars to install, one per line, and works exactly the same as listing them on the command line. Each jar is installed to debian/$package/usr/share/java/ in the appropriate versioned and unversioned forms.

If the jars built by upstream already contain the version number, this will be stripped before installing. `jh_installlibs` will also try to strip the upstream version number of any dfsg suffix. Other version-mangling options or explicit version numbers can also be provided.

## jh_depends

`jh_depends` works like `dpkg-shlibdeps`, but for jar files. For each jar in the package it takes the jars on which it depends and finds the packages to which they belong. These are included in the debhelper substvars as ${java:Depends}. The control file can then just list that variable which is filled in automatically.

This is done by reading the Class-Path attribute from the manifest of each jar. Jar files should include this attribute to prevent applications which use them from needing a full recursive classpath in their startup scripts and to prevent unneccessary transitions when the library changes its dependencies. If the package is not built with `jh_build` and the upstream build system does not set it correctly then `jh_manifest` or `jh_classpath` can be used to fix this.

If the application uses executable jars (see Runtime support below) then `jh_depends` will also add the appropriate depends on jarwrapper and the correct Java runtime.

As of version 0.32, `jh_depends` also checks installed javadocs for links to system installed javadocs. It will use this to populate the ${java:Recommends} variable, which can be used for the doc package.

Note that both substvars are always created even if they are empty, like debhelper does with ${misc:Depends}.

## jh_manifest

Many upstream build systems do not set the Class-Path attribute in the jars they create. This leads to several unwanted problems, such as expanding the classpath which applications have to use and introducing unneccessary transitions. They also may not set the Main-Class attribute. Both of these are required for running jars with the -jar parameter.

`jh_manifest` can fix the manifest files of jars. It can either read from a manifest file in the Debian directory or run in a mode which updates all the jars with the `CLASSPATH` environment variable.

The manifest files can either be debian/package.manifest or debian/manifest. The format of this file is a list of jars and indented below each one a list of manifest elements to set:

    usr/share/weirdx/weirdx.jar:
     Main-Class: com.jcraft.weirdx.WeirdX
     Debian-Java-Home: /usr/lib/jvm/default-java

Note: Prior to javahelper 0.32 (0.33 if you used cdbs), `jh_manifest` would be run before `jh_installlibs`. In these versions the jars were usually referred to by their location in the build directories rather than their install location.

## jh_classpath

If you are just setting the classpath then this command is simpler than `jh_manifest`. `jh_classpath` can either take jars on the command line with the classpath specified on the command line or in the `CLASSPATH` environment variable.

Alternatively, it can read classpaths from a debian/classpath or debian/package.classpath file. This should be one jar per line specifying the jar followed by it's space-separated classpath:

    usr/share/java/bar.jar /usr/share/java/quux.jar
    usr/share/java/foo.jar /usr/share/java/bar.jar /usr/share/java/baz.jar

Note: Prior to javahelper 0.32 (0.33 if you used cdbs), `jh_classpath` would be run before `jh_installlibs`. In these versions the jars were usually referred to by their location in the build directories rather than their install location.

## jh_exec

The Runtime support section below describes running executable jars directly. `jh_exec` will scan package directories for jars in the paths, or symlinks to jar from the paths, and ensure that they have been set executable if necessary.

## jh_installjavadoc

If you have javadoc which has been built by your build system, then `jh_installjavadoc` will install it in the correct location and register it with doc-base for you. Either run `jh_installjavadoc` with the directory containing the javadoc as a parameter, or it will read debian/javadoc or debian/$package.javadoc which should contain a single path to the javadoc for that package.

If you have used `jh_build` that will automatically have created javadoc. To install that put the string "internal" in the javadoc file and it will be installed.

The second parameter, or the second string on the line in the javadoc file, can be used to override the install location, for example, so that a -doc package can install to /usr/share/doc/$library/api.

## jh_linkjars

If upstream ship convenience copies of third-party jar files which have been removed (see `jh_repack` below), but the build system refers to that directory, `jh_linkjars` can be used to populate the directory with symlinks to the packaged jars in /usr/share/java.

It is called either with a directory on the command line or by specifying one target directory per line in the file debian/linkjars.

`jh_linkjars` will scan all of the (installed) build-dependencies and create a symlink to every jar which is installed by those packages in the target directory.

`jh_linkjars` can be called with -u to remove all the symlinks in the clean target. This is done automatically by `jh_clean`.

## jh_clean

`jh_clean` removes any files which have been created during the build by other `jh_` commands, such as `jh_build` and `jh_linkjars`

## jh_makepkg

`jh_makepkg` will create template Debian packages for Java programs and libraries similar to `dh-make`. It should be run in the source directory and it will create the orig.tar.gz and most of the files in the Debian directory, which need only small changes neccessary to build the package.

## jh_repack

`jh_repack` provides functionality to help clean your upstream tarball of prebuilt jars, classfiles and javadoc. If you want to do this whenever you download a new version you can use `jh_repack` as a uscan helper. Just put `jh_repack` as the command at the end of the uscan line. E.g.

    version=3
    http://www.matthew.ath.cx/projects/salliere/ (?:.*/)?salliere-?_?([\d+\.]+|\d+)\.(tar.*|tgz|zip|gz|bz2|) debian jh_repack

Alternatively you can run it by hand:

    jh_repack --upstream-version <version> <tarball>

`jh_repack` will remove any .class files, any .jar files, the whole directory tree containing javadoc and any empty directories as a result of the above.

## java-propose-classpath

Some upstreams have complicated classpaths which may not be obvious to the packager when using `jh_manifest` to set the Class-Path attribute. `java-propose-classpath` will unpack a jar and look at the symbols imported to the class files, then scan all the jars in /usr/share/java. This should not be run in the build since it is slow, and there may be ambiguities that the packager must resolve. It is still very useful for the packager as most of the time it will get it right automatically.

To avoid bloating the recursive build-deps of packages, `java-propose-classpath` is in a separate package to javahelper. It should not be on any package's build-depends.

## jh_installeclipse

`jh_installeclipse` will install eclipse features built by eclipse's pde-build script. It supports most of debhelpers normal options. Features can either be put in the $package.eh-install or be given per command-line. By default `jh_installeclipse` expects pde-build to have been run from debian/.eclipse-build; if you decide to run it from another directory, you should use --pde-build-dir to tell `jh_installeclipse` where pde-build was run from.

`jh_installeclipse` knows where pde-build dumps its output, so only the name of the feature should be given. It supports file globbing both in the files and per command-line (though in the latter case your shell may attempt to expand the globs if they are not properly escaped or quoted).

Due two the way the underlying build system works; orbit dependencies will be embedded directly into the installation. `jh_installeclipse` will replace any orbit dependencies imported by `jh_generateorbitdir`. If you add/import orbit dependencies yourself through other means, you must replace them yourselves after running `jh_installeclipse`.

Finally, `jh_installeclipse` will output a ${orbit:Depends} variable if it replaces any orbit dependency for that package.

## jh_generateorbitdir

`jh_generateorbitdir` is an javahelper program that handles creation of an orbit dependency dir. This directory has to be populated with non-eclipse jar files. However, eclipse refers to these jars by their "symbolic name". `jh_generateorbitdir` can extract this name from the jar's manifest (provided it has the OSGi metadata) and create a symlink to it.

`jh_generateorbitdir` will replace regular files with symlinks if they are present in the orbit dir and clash with the name of one of the orbit jars. If an orbit jar name clashes with a symlink in the orbit dir, then `jh_generateorbitdir` will assume that the given jar has already been symlinked and skip it.

`jh_generateorbitdir` will also check the default installation for jar files on Debian systems (at the time of writing /usr/share/java), if it cannot find the jar in the current dir.

If present, `jh_generateorbitdir` will read debian/eclipse.orbitdeps and add the jar files listed in it to the list of orbit dependencies.

## jh_setupenvironment

`jh_setupenvironment` is a javahelper program that handles creating an environment for building an eclipse feature. It does not setup an orbit dir (use `jh_generateorbitdir` for that). It will copy files specified in debian/eclipse.environment as well as those given on command line into the environment dir. If no files are given per command line and the environment file is not present (or is empty), it will default to org.eclipse.*

## jh_compilefeatures

`jh_compilefeatures` handles compilation of eclipse features. It will read debian/eclipse.features as a list of features to compile and their dependencies. The first item on a line is the id of the feature and the remaining are either ids of previously compiled features or features installed on the system (identified by the folder they are installed in).

By default `jh_compilefeatures` will set the source and the target version of the class files to 1.5. This can be overriden by explicitly changing the build options (see man `jh_compilefeatures` for more information).

## java-vars.mk

You can include /usr/share/javahelper/java-vars.mk in your debian/rules to get the following variables defined:

- `JAVA_HOME`

  If you have not already set it, will default to the default JDK for the architecture (you must depend on default-jdk or -headless if you are not overriding this). To override this set `JAVA_HOME` before including java-vars.mk

- `JAVA_ARCH`

  The JVM version of the build architecture (eg ppc not powerpc)

- `JRE_HOME`

  If `$JAVA_HOME/jre` exists then that, otherwise `$JAVA_HOME`

- `JVM_CLIENT_DIR` and `JVM_SERVER_DIR`

  Set if the respective types of JVM are installed.

If you need the Java architecture in a non-make context then you can use /usr/share/javahelper/java-arch.sh instead.

# Runtime support

Javatools also provides some runtime support. Unlike compiled programs, or purely interpreted programs with hash-bang lines, Java programs cannot be directly executed. Many upstreams expect them to be run using java -jar jarname or java classname. This is not generally acceptible in systems which expect to just be able to run the command or launch it from a menu. As a result, many packagers are writing wrapper scripts which just call java with the correct classpath, jar and main class.

## jarwrapper

There is an alternative to wrapper scripts, however. The binfmt_misc kernel module allows the kernel to call out to a program in userspace to execute specific types of file. jarwrapper registers itself as a handler for executable jars. This is done by reading values from the manifest file.

In order for executable jars to work the following attributes must or may be defined in the manifest. These attributes can be set using `jh_build` and `jh_manifest`.

- Main-Class: The name of the class to be run when the application starts. (REQUIRED)

- Class-Path: The path to all the jar files on which this jar depends. (REQUIRED unless empty)

- Debian-Java-Home: A Debian-specific property if this application depends on a specific runtime. Specify the path to the runtime which should be used. Multiple space-separated paths may be given if any of the runtimes will work. (OPTIONAL)

- Debian-Java-Parameters: A Debian-specific property if this application needs extra options to the JVM. (OPTIONAL)

## Java Architecture

If you need to know the JVM architecture name at runtime (for example to put libjvm.so on the `LD_LIBRARY_PATH`) then jarwrapper also provides /usr/share/jarwrapper/java-arch.sh which will either print the current one or convert a debian arch name to a JVM arch name.

# Putting it together

This section shows the debian packaging generated by `jh_makepkg` for an application and a library using `jh_build`.

## Sample Library Packaging

debian/control

    Source: jsch
    Section: java
    Priority: optional
    Maintainer: Matthew Johnson <mjj29@debian.org>
    Build-Depends: debhelper (>= 7), javahelper, default-jdk, libzlib-java
    Standards-Version: 3.9.1
    Homepage: http://www.jcraft.com/jsch/

    Package: libjsch-java
    Architecture: all
    Depends: ${java:Depends}, ${misc:Depends}
    Description: Java secure channel
     JSch is a pure Java implementation of SSH2. JSch allows you to
     connect to an sshd server and use port forwarding, X11 forwarding,
     file transfer, etc., and you can integrate its functionality
     into your own Java programs. JSch is licensed under a BSD style
     license.

debian/rules

    #!/usr/bin/make -f

    export JAVA_HOME=/usr/lib/jvm/default-java
    export CLASSPATH=/usr/share/java/zlib.jar

    build: build-stamp
    build-stamp:
        dh_testdir
        jh_build jsch.jar src
        touch $@

    clean:
        dh_testdir
        dh_testroot
        jh_build --clean
        dh_clean
        rm -f build-stamp jsch.jar

    install: build
        dh_testdir
        dh_testroot
        dh_prep
        dh_installdirs

    binary-arch: build install
        # Java packages are arch: all, nothing to do here

    binary-indep: build install
        # Create the package here
        dh_testdir
        dh_testroot
        dh_prep
        dh_install -i
        jh_installjavadoc -i
        dh_installdocs -i
        dh_installchangelogs -i
        jh_installlibs -i
        jh_depends -i
        dh_compress -i
        dh_fixperms -i
        dh_installdeb -i
        dh_gencontrol -i
        dh_md5sums -i
        dh_builddeb -i

    binary: binary-indep binary-arch
    .PHONY: build clean binary-indep binary-arch binary install

debian/libjsch-java.jlibs

    jsch.jar

debian/libjsch-java.javadoc

    internal

## Sample Application Packaging

debian/control

    Source: salliere
    Section: misc
    Priority: optional
    Maintainer: Matthew Johnson <mjj29@debian.org>
    Build-Depends: debhelper (>= 7), default-jdk,
                   libmatthew-debug-java, libcsv-java,
                   libitext-java, javahelper
    Standards-Version: 3.9.1

    Package: salliere
    Architecture: all
    Depends: ${java:Depends}, ${misc:Depends}
    Description: Short Description
     Long Description

debian/rules

    #!/usr/bin/make -f
    export JAVA_HOME=/usr/lib/jvm/default-java
    export CLASSPATH=/usr/share/java/csv.jar:/usr/share/java/debug-disable.jar:/usr/share/java/itext.jar

    build: build-stamp
    build-stamp:
        dh_testdir
        # Build the package
        jh_build salliere.jar src
        touch $@

    clean:
        dh_testdir
        dh_testroot
        rm -f build-stamp salliere.jar
        jh_build --clean
        dh_clean

    install: build
        dh_testdir
        dh_testroot
        dh_prep
        dh_installdirs

    binary-arch: build install
        # Java packages are arch: all, nothing to do here

    binary-indep: build install
        # Create the package here
        dh_testdir
        dh_testroot
        dh_prep
        dh_install -i
        dh_installdocs -i
        dh_installchangelogs -i
        jh_manifest -i
        dh_link -i
        jh_exec -i
        jh_depends -i
        dh_compress -i
        dh_fixperms -i
        dh_installdeb -i
        dh_gencontrol -i
        dh_md5sums -i
        dh_builddeb -i

    binary: binary-indep binary-arch
    .PHONY: build clean binary-indep binary-arch binary install

debian/salliere.install

    salliere.jar usr/share/salliere

debian/salliere.links

    usr/share/salliere/salliere.jar usr/bin

## Using javahelper with CDBS

Javahelper 0.18 introduces a CDBS class for javahelper. It runs all the `jh_` commands after `dh_install*` and `dh_link` and has options for running `jh_build` under the build target.

The `jh_` commands are invoked once per package. You can pass options to all the invocations using the `JH_EXEC_ARGS`, `JH_INSTALLLIBS_ARGS`, `JH_MANIFEST_ARGS` and `JH_DEPENDS_ARGS` variables.

To invoke `jh_build` you must either set `JH_BUILD_JAR` and `JH_BUILD_SOURCE` and `JAVA_HOME` or have a debian/javabuild file and set `JAVA_HOME`. Optionally you can also set `CLASSPATH` and `JH_BUILD_ARGS`.

Please note: you MUST include javahelper.mk before ant.mk.

The above debian/rules can be rewritten with CDBS as follows:

    #!/usr/bin/make -f
    export JAVA_HOME=/usr/lib/jvm/default-java
    export CLASSPATH=/usr/share/java/csv.jar:/usr/share/java/debug-disable.jar:/usr/share/java/itext.jar
    JH_BUILD_JAR=salliere.jar
    JH_BUILD_SRC=src

    include /usr/share/cdbs/1/class/javahelper.mk

## Using javahelper with dh

Javahelper 0.20 introduces a dh extension for javahelper. It runs all the `jh_` commands after `dh_install*` and `dh_link` and also runs `jh_build` if you have a debian/javabuild file.

The above debian/rules can be rewritten with dh 7 as follows:

debian/javabuild

    salliere.jar src

debian/rules

    #!/usr/bin/make -f

    export JAVA_HOME=/usr/lib/jvm/default-java
    export CLASSPATH=/usr/share/java/csv.jar:/usr/share/java/debug-disable.jar:/usr/share/java/itext.jar

    %:
        dh $@ --with javahelper