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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 <title>Java</title>
5
6 <para>
7 Ant-based Java packages are typically built from source as follows:
8<programlisting>
9stdenv.mkDerivation {
10 name = "...";
11 src = fetchurl { ... };
12
13 buildInputs = [ jdk ant ];
14
15 buildPhase = "ant";
16}
17</programlisting>
18 Note that <varname>jdk</varname> is an alias for the OpenJDK (self-built
19 where available, or pre-built via Zulu). Platforms with OpenJDK not (yet) in
20 Nixpkgs (<literal>Aarch32</literal>, <literal>Aarch64</literal>) point to the
21 (unfree) <literal>oraclejdk</literal>.
22 </para>
23
24 <para>
25 JAR files that are intended to be used by other packages should be installed
26 in <filename>$out/share/java</filename>. JDKs have a stdenv setup hook that
27 add any JARs in the <filename>share/java</filename> directories of the build
28 inputs to the <envar>CLASSPATH</envar> environment variable. For instance, if
29 the package <literal>libfoo</literal> installs a JAR named
30 <filename>foo.jar</filename> in its <filename>share/java</filename>
31 directory, and another package declares the attribute
32<programlisting>
33buildInputs = [ jdk libfoo ];
34</programlisting>
35 then <envar>CLASSPATH</envar> will be set to
36 <filename>/nix/store/...-libfoo/share/java/foo.jar</filename>.
37 </para>
38
39 <para>
40 Private JARs should be installed in a location like
41 <filename>$out/share/<replaceable>package-name</replaceable></filename>.
42 </para>
43
44 <para>
45 If your Java package provides a program, you need to generate a wrapper
46 script to run it using the OpenJRE. You can use
47 <literal>makeWrapper</literal> for this:
48<programlisting>
49buildInputs = [ makeWrapper ];
50
51installPhase =
52 ''
53 mkdir -p $out/bin
54 makeWrapper ${jre}/bin/java $out/bin/foo \
55 --add-flags "-cp $out/share/java/foo.jar org.foo.Main"
56 '';
57</programlisting>
58 Note the use of <literal>jre</literal>, which is the part of the OpenJDK
59 package that contains the Java Runtime Environment. By using
60 <literal>${jre}/bin/java</literal> instead of
61 <literal>${jdk}/bin/java</literal>, you prevent your package from depending
62 on the JDK at runtime.
63 </para>
64
65 <para>
66 Note all JDKs passthru <literal>home</literal>, so if your application
67 requires environment variables like <envar>JAVA_HOME</envar> being set, that
68 can be done in a generic fashion with the <literal>--set</literal> argument
69 of <literal>makeWrapper</literal>:
70<programlisting>
71 --set JAVA_HOME ${jdk.home}
72</programlisting>
73 </para>
74
75 <para>
76 It is possible to use a different Java compiler than <command>javac</command>
77 from the OpenJDK. For instance, to use the GNU Java Compiler:
78<programlisting>
79buildInputs = [ gcj ant ];
80</programlisting>
81 Here, Ant will automatically use <command>gij</command> (the GNU Java
82 Runtime) instead of the OpenJRE.
83 </para>
84</section>