Java Reference
In-Depth Information
WARNING: WHEN BND GOES BAD
When using bnd, it's essential to inspect
both your bundle contents and your manifest after building, at least while
you're getting started. Small misunderstandings between you and bnd can
result in
Every package in your bundle being exported
■
All
of your dependencies being included in your bundle
■
None of your classes being repackaged in your bundle
■
The authors are aware of these possibilities because we've made all of these
mistakes ourselves! You'll quickly discover if your classes haven't been
included in your bundle, but the other two issues may take much longer to
notice; your built bundle will be perfectly valid, but it won't be at all encapsu-
lated, or at all modular, so it's not in the
spirit
of
OSG
i.
We've been talking about building using bnd, but what you're doing here is some-
where halfway between building and packaging. The way you're using it, the bnd tool
isn't compiling anything; all it's doing is using the precompiled code to generate a
manifest, and then packaging everything up into a
JAR
.
PACKAGE VERSIONS
When you used bnd to build the
fancyfoods.persistence
bundle, it added in pack-
age imports, but no versions. Because specifying versions is an
OSG
i best practice, it
would be annoying if bnd always ignored them. Luckily, bnd will take good care of
your versions if provided with the right information.
Bnd can't guess the version of exported packages from their bytecode, so the ver-
sion must be specified somewhere. One option is to explicitly list the packages in the
Export-Package
and provide a version for each one, but this is manual, and undoes
some of the benefits of bnd wildcards. A nicer solution is to make use of bnd's sup-
port for Java
package-info.java
files. A
package-info
file is a special class whose
only content is an annotation specifying the version. Because the
package-info
files
are right next to the source, it's easier to remember to update them when making
code changes.
An alternative to
package-info.java
Some people dislike the extra overhead of maintaining a class to represent information
about their Java packages. As an alternative option, bnd also looks for text files called
packageinfo
in each package. These
packageinfo
files use the properties format,
but otherwise can contain exactly the same information as
package-info.java
.
Any of the tricks we show you for managing
package-info.java
will work equally
well in a
packageinfo
file.
Bnd will automatically detect
package-info
files and use them to determine the ver-
sion of exported packages. For example, to set the version of the
fancyfoods.food
