85 lines
2.6 KiB
XML
85 lines
2.6 KiB
XML
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="sec-language-java">
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<title>Java</title>
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<para>Ant-based Java packages are typically built from source as follows:
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<programlisting>
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stdenv.mkDerivation {
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name = "...";
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src = fetchurl { ... };
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buildInputs = [ jdk ant ];
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buildPhase = "ant";
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}
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</programlisting>
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Note that <varname>jdk</varname> is an alias for the OpenJDK.</para>
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<para>JAR files that are intended to be used by other packages should
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be installed in <filename>$out/share/java</filename>. The OpenJDK has
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a stdenv setup hook that adds any JARs in the
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<filename>share/java</filename> directories of the build inputs to the
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<envar>CLASSPATH</envar> environment variable. For instance, if the
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package <literal>libfoo</literal> installs a JAR named
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<filename>foo.jar</filename> in its <filename>share/java</filename>
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directory, and another package declares the attribute
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<programlisting>
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buildInputs = [ jdk libfoo ];
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</programlisting>
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then <envar>CLASSPATH</envar> will be set to
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<filename>/nix/store/...-libfoo/share/java/foo.jar</filename>.</para>
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<para>Private JARs
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should be installed in a location like
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<filename>$out/share/<replaceable>package-name</replaceable></filename>.</para>
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<para>If your Java package provides a program, you need to generate a
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wrapper script to run it using the OpenJRE. You can use
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<literal>makeWrapper</literal> for this:
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<programlisting>
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buildInputs = [ makeWrapper ];
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installPhase =
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''
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mkdir -p $out/bin
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makeWrapper ${jre}/bin/java $out/bin/foo \
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--add-flags "-cp $out/share/java/foo.jar org.foo.Main"
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'';
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</programlisting>
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Note the use of <literal>jre</literal>, which is the part of the
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OpenJDK package that contains the Java Runtime Environment. By using
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<literal>${jre}/bin/java</literal> instead of
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<literal>${jdk}/bin/java</literal>, you prevent your package from
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depending on the JDK at runtime.</para>
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<para>It is possible to use a different Java compiler than
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<command>javac</command> from the OpenJDK. For instance, to use the
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Eclipse Java Compiler:
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<programlisting>
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buildInputs = [ jre ant ecj ];
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</programlisting>
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(Note that here you don’t need the full JDK as an input, but just the
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JRE.) The ECJ has a stdenv setup hook that sets some environment
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variables to cause Ant to use ECJ, but this doesn’t work with all Ant
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files. Similarly, you can use the GNU Java Compiler:
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<programlisting>
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buildInputs = [ gcj ant ];
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</programlisting>
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Here, Ant will automatically use <command>gij</command> (the GNU Java
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Runtime) instead of the OpenJRE.</para>
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</section>
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