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