Generic Java Builds

This chapter talks about basic build steps in Java such as invoking javac and using spec macros like build-claspath and build-jar-repository.

Generating Application Shell Scripts

As mentioned in section about Java packaging basics, all Java applications need wrapper shell scripts to setup the environment before running JVM and associated Java code.

The javapackages-tools package contains a convenience %jpackage_script macro that can be used to create scripts that work for the majority of packages. See its definition and documentation in /usr/lib/rpm/macros.d/macros.jpackage. One thing to pay attention to is the 6th argument to it - whether to prefer a JRE over a full SDK when looking up a JVM to invoke. Most packages that do not require the full Java SDK will want to set that to true to avoid unexpected results when looking up a JVM when some of the installed JREs do not have the corresponding SDK (*-devel package) installed.

%install
...
%jpackage_script msv.textui.Driver "" "" msv-msv:msv-xsdlib:relaxngDatatype:isorelax msv true
...

The previous example installs the msv script (5th argument) with main class being msv.textui.Driver (1st argument). No optional flags (2nd argument) or options (3rd argument) are used. This script will add several libraries to classpath before executing main class (4th argument, JAR files separated with :). build-classpath is run on every part of 4th argument to create full classpaths.

Replacing JARs with symlinks using xmvn-subst

Sometimes it may be needed to replace all JAR files in current directory with symlinks to the system JARs located in %{_javadir}. This task can be achieved using tool called xmvn-subst.

$ ls -l
-rw-r--r--. 1 msrb msrb  40817 Oct 22 09:16 cli.jar
-rw-r--r--. 1 msrb msrb 289983 Oct 22 09:17 junit4.jar
-rw-r--r--. 1 msrb msrb 474276 Oct 22 09:14 log4j.jar
$ xmvn-subst .
[INFO] Linked ./cli.jar to /usr/share/java/commons-cli.jar
[INFO] Linked ./log4j.jar to /usr/share/java/log4j.jar
[INFO] Linked ./junit4.jar to /usr/share/java/junit.jar
$ ls -la
lrwxrwxrwx. 1 msrb msrb   22 Oct 22 10:08 cli.jar -> /usr/share/java/commons-cli.jar
lrwxrwxrwx. 1 msrb msrb   22 Oct 22 10:08 junit4.jar -> /usr/share/java/junit.jar
lrwxrwxrwx. 1 msrb msrb   22 Oct 22 10:08 log4j.jar -> /usr/share/java/log4j.jar

The example above shows how easy the symlinking can be. However, there are some limitations. Original JAR files need to carry metadata which tell xmvn-subst for what artifact given file should be substituted. Otherwise xmvn-subst won’t be able to identify the Maven artifact from JAR file.

See xmvn-subst -h for all available options.

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