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1<section xmlns="http://docbook.org/ns/docbook"
2 xmlns:xlink="http://www.w3.org/1999/xlink"
3 xml:id="sec-language-java">
4
5<title>Java</title>
6
7<para>Ant-based Java packages are typically built from source as follows:
8
9<programlisting>
10stdenv.mkDerivation {
11 name = "...";
12 src = fetchurl { ... };
13
14 buildInputs = [ jdk ant ];
15
16 buildPhase = "ant";
17}
18</programlisting>
19
20Note that <varname>jdk</varname> is an alias for the OpenJDK.</para>
21
22<para>JAR files that are intended to be used by other packages should
23be installed in <filename>$out/share/java</filename>. The OpenJDK has
24a stdenv setup hook that adds any JARs in the
25<filename>share/java</filename> directories of the build inputs to the
26<envar>CLASSPATH</envar> environment variable. For instance, if the
27package <literal>libfoo</literal> installs a JAR named
28<filename>foo.jar</filename> in its <filename>share/java</filename>
29directory, and another package declares the attribute
30
31<programlisting>
32buildInputs = [ jdk libfoo ];
33</programlisting>
34
35then <envar>CLASSPATH</envar> will be set to
36<filename>/nix/store/...-libfoo/share/java/foo.jar</filename>.</para>
37
38<para>Private JARs
39should be installed in a location like
40<filename>$out/share/<replaceable>package-name</replaceable></filename>.</para>
41
42<para>If your Java package provides a program, you need to generate a
43wrapper script to run it using the OpenJRE. You can use
44<literal>makeWrapper</literal> for this:
45
46<programlisting>
47buildInputs = [ makeWrapper ];
48
49installPhase =
50 ''
51 mkdir -p $out/bin
52 makeWrapper ${jre}/bin/java $out/bin/foo \
53 --add-flags "-cp $out/share/java/foo.jar org.foo.Main"
54 '';
55</programlisting>
56
57Note the use of <literal>jre</literal>, which is the part of the
58OpenJDK package that contains the Java Runtime Environment. By using
59<literal>${jre}/bin/java</literal> instead of
60<literal>${jdk}/bin/java</literal>, you prevent your package from
61depending on the JDK at runtime.</para>
62
63<para>It is possible to use a different Java compiler than
64<command>javac</command> from the OpenJDK. For instance, to use the
65Eclipse Java Compiler:
66
67<programlisting>
68buildInputs = [ jre ant ecj ];
69</programlisting>
70
71(Note that here you don’t need the full JDK as an input, but just the
72JRE.) The ECJ has a stdenv setup hook that sets some environment
73variables to cause Ant to use ECJ, but this doesn’t work with all Ant
74files. Similarly, you can use the GNU Java Compiler:
75
76<programlisting>
77buildInputs = [ gcj ant ];
78</programlisting>
79
80Here, Ant will automatically use <command>gij</command> (the GNU Java
81Runtime) instead of the OpenJRE.</para>
82
83</section>
84