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<?xml version='1.0'?>
<!DOCTYPE sconsdoc [
<!ENTITY % scons SYSTEM "../scons.mod">
%scons;
<!ENTITY % builders-mod SYSTEM "../generated/builders.mod">
%builders-mod;
<!ENTITY % functions-mod SYSTEM "../generated/functions.mod">
%functions-mod;
<!ENTITY % tools-mod SYSTEM "../generated/tools.mod">
%tools-mod;
<!ENTITY % variables-mod SYSTEM "../generated/variables.mod">
%variables-mod;
]>
<chapter id="chap-java"
xmlns="http://www.scons.org/dbxsd/v1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 scons.xsd">
<title>Java Builds</title>
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WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-->
<para>
So far, we've been using examples of
building C and C++ programs
to demonstrate the features of &SCons;.
&SCons; also supports building Java programs,
but Java builds are handled slightly differently,
which reflects the ways in which
the Java compiler and tools
build programs differently than
other languages' tool chains.
</para>
<section>
<title>Building Java Class Files: the &b-Java; Builder</title>
<para>
The basic activity when programming in Java,
of course, is to take one or more <filename>.java</filename> files
containing Java source code
and to call the Java compiler
to turn them into one or more
<filename>.class</filename> files.
In &SCons;, you do this
by giving the &b-link-Java; Builder
a target directory in which
to put the <filename>.class</filename> files,
and a source directory that contains
the <filename>.java</filename> files:
</para>
<scons_example name="java_java">
<file name="SConstruct" printme="1">
Java('classes', 'src')
</file>
<file name="src/Example1.java">
public class Example1
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="src/Example2.java">
public class Example2
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="src/Example3.java">
public class Example3
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
</scons_example>
<para>
If the <filename>src</filename> directory contains
three <filename>.java</filename> source files,
then running &SCons; might look like this:
</para>
<scons_output example="java_java">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
&SCons; will actually search the <filename>src</filename>
directory tree for all of the <filename>.java</filename> files.
The Java compiler will then create the
necessary class files in the <filename>classes</filename> subdirectory,
based on the class names found in the <filename>.java</filename> files.
</para>
</section>
<section>
<title>How &SCons; Handles Java Dependencies</title>
<para>
In addition to searching the source directory for
<filename>.java</filename> files,
&SCons; actually runs the <filename>.java</filename> files
through a stripped-down Java parser that figures out
what classes are defined.
In other words, &SCons; knows,
without you having to tell it,
what <filename>.class</filename> files
will be produced by the &javac; call.
So our one-liner example from the preceding section:
</para>
<scons_example name="java_java-classes">
<file name="SConstruct" printme="1">
Java('classes', 'src')
</file>
<file name="src/Example1.java">
public class Example1
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
public class AdditionalClass1
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="src/Example2.java">
public class Example2
{
class Inner2 {
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
}
</file>
<file name="src/Example3.java">
public class Example3
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
public class AdditionalClass3
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
</scons_example>
<para>
Will not only tell you reliably
that the <filename>.class</filename> files
in the <filename>classes</filename> subdirectory
are up-to-date:
</para>
<scons_output example="java_java-classes">
<scons_output_command suffix="1">scons -Q</scons_output_command>
<scons_output_command suffix="2">scons -Q classes</scons_output_command>
</scons_output>
<para>
But it will also remove all of the generated
<filename>.class</filename> files,
even for inner classes,
without you having to specify them manually.
For example, if our
<filename>Example1.java</filename>
and
<filename>Example3.java</filename>
files both define additional classes,
and the class defined in <filename>Example2.java</filename>
has an inner class,
running <userinput>scons -c</userinput>
will clean up all of those <filename>.class</filename> files
as well:
</para>
<scons_output example="java_java-classes">
<scons_output_command suffix="3">scons -Q</scons_output_command>
<scons_output_command suffix="4">scons -Q -c classes</scons_output_command>
</scons_output>
<para>
To ensure correct handling of <filename>.class</filename>
dependencies in all cases, you need to tell &SCons; which Java
version is being used. This is needed because Java 1.5 changed
the <filename>.class</filename> file names for nested anonymous
inner classes. Use the <varname>JAVAVERSION</varname> construction
variable to specify the version in use. With Java 1.6, the
one-liner example can then be defined like this:
</para>
<sconstruct>
Java('classes', 'src', JAVAVERSION='1.6')
</sconstruct>
<para>
See <varname>JAVAVERSION</varname> in the man page for more information.
</para>
</section>
<section>
<title>Building Java Archive (<filename>.jar</filename>) Files: the &b-Jar; Builder</title>
<para>
After building the class files,
it's common to collect them into
a Java archive (<filename>.jar</filename>) file,
which you do by calling the &b-link-Jar; Builder method.
If you want to just collect all of the
class files within a subdirectory,
you can just specify that subdirectory
as the &b-Jar; source:
</para>
<scons_example name="java_jar1">
<file name="SConstruct" printme="1">
Java(target = 'classes', source = 'src')
Jar(target = 'test.jar', source = 'classes')
</file>
<file name="src/Example1.java">
public class Example1
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="src/Example2.java">
public class Example2
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="src/Example3.java">
public class Example3
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
</scons_example>
<para>
&SCons; will then pass that directory
to the &jar; command,
which will collect all of the underlying
<filename>.class</filename> files:
</para>
<scons_output example="java_jar1">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
If you want to keep all of the
<filename>.class</filename> files
for multiple programs in one location,
and only archive some of them in
each <filename>.jar</filename> file,
you can pass the &b-Jar; builder a
list of files as its source.
It's extremely simple to create multiple
<filename>.jar</filename> files this way,
using the lists of target class files created
by calls to the &b-link-Java; builder
as sources to the various &b-Jar; calls:
</para>
<scons_example name="java_jar2">
<file name="SConstruct" printme="1">
prog1_class_files = Java(target = 'classes', source = 'prog1')
prog2_class_files = Java(target = 'classes', source = 'prog2')
Jar(target = 'prog1.jar', source = prog1_class_files)
Jar(target = 'prog2.jar', source = prog2_class_files)
</file>
<file name="prog1/Example1.java">
public class Example1
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="prog1/Example2.java">
public class Example2
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="prog2/Example3.java">
public class Example3
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
<file name="prog2/Example4.java">
public class Example4
{
public static void main(String[] args)
{
System.out.println("Hello Java world!\n");
}
}
</file>
</scons_example>
<para>
This will then create
<filename>prog1.jar</filename>
and <filename>prog2.jar</filename>
next to the subdirectories
that contain their <filename>.java</filename> files:
</para>
<scons_output example="java_jar2">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Building C Header and Stub Files: the &b-JavaH; Builder</title>
<para>
You can generate C header and source files
for implementing native methods,
by using the &b-link-JavaH; Builder.
There are several ways of using the &JavaH; Builder.
One typical invocation might look like:
</para>
<scons_example name="java_javah">
<file name="SConstruct" printme="1">
classes = Java(target = 'classes', source = 'src/pkg/sub')
JavaH(target = 'native', source = classes)
</file>
<file name="src/pkg/sub/Example1.java">
package pkg.sub;
public class Example1
{
public static void main(String[] args)
{
}
}
</file>
<file name="src/pkg/sub/Example2.java">
package pkg.sub;
public class Example2
{
public static void main(String[] args)
{
}
}
</file>
<file name="src/pkg/sub/Example3.java">
package pkg.sub;
public class Example3
{
public static void main(String[] args)
{
}
}
</file>
</scons_example>
<para>
The source is a list of class files generated by the
call to the &b-link-Java; Builder,
and the target is the output directory in
which we want the C header files placed.
The target
gets converted into the <option>-d</option>
when &SCons; runs &javah;:
</para>
<scons_output example="java_javah">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
In this case,
the call to &javah;
will generate the header files
<filename>native/pkg_sub_Example1.h</filename>,
<filename>native/pkg_sub_Example2.h</filename>
and
<filename>native/pkg_sub_Example3.h</filename>.
Notice that &SCons; remembered that the class
files were generated with a target directory of
<filename>classes</filename>,
and that it then specified that target directory
as the <option>-classpath</option> option
to the call to &javah;.
</para>
<para>
Although it's more convenient to use
the list of class files returned by
the &b-Java; Builder
as the source of a call to the &b-JavaH; Builder,
you <emphasis>can</emphasis>
specify the list of class files
by hand, if you prefer.
If you do,
you need to set the
&cv-link-JAVACLASSDIR; construction variable
when calling &b-JavaH;:
</para>
<scons_example name="java_JAVACLASSDIR">
<file name="SConstruct" printme="1">
Java(target = 'classes', source = 'src/pkg/sub')
class_file_list = ['classes/pkg/sub/Example1.class',
'classes/pkg/sub/Example2.class',
'classes/pkg/sub/Example3.class']
JavaH(target = 'native', source = class_file_list, JAVACLASSDIR = 'classes')
</file>
<file name="src/pkg/sub/Example1.java">
package pkg.sub;
public class Example1
{
public static void main(String[] args)
{
}
}
</file>
<file name="src/pkg/sub/Example2.java">
package pkg.sub;
public class Example2
{
public static void main(String[] args)
{
}
}
</file>
<file name="src/pkg/sub/Example3.java">
package pkg.sub;
public class Example3
{
public static void main(String[] args)
{
}
}
</file>
</scons_example>
<para>
The &cv-JAVACLASSDIR; value then
gets converted into the <option>-classpath</option>
when &SCons; runs &javah;:
</para>
<scons_output example="java_JAVACLASSDIR">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
Lastly, if you don't want a separate header file
generated for each source file,
you can specify an explicit File Node
as the target of the &b-JavaH; Builder:
</para>
<scons_example name="java_javah_file">
<file name="SConstruct" printme="1">
classes = Java(target = 'classes', source = 'src/pkg/sub')
JavaH(target = File('native.h'), source = classes)
</file>
<file name="src/pkg/sub/Example1.java">
package pkg.sub;
public class Example1
{
public static void main(String[] args)
{
}
}
</file>
<file name="src/pkg/sub/Example2.java">
package pkg.sub;
public class Example2
{
public static void main(String[] args)
{
}
}
</file>
<file name="src/pkg/sub/Example3.java">
package pkg.sub;
public class Example3
{
public static void main(String[] args)
{
}
}
</file>
</scons_example>
<para>
Because &SCons; assumes by default
that the target of the &b-JavaH; builder is a directory,
you need to use the &File; function
to make sure that &SCons; doesn't
create a directory named <filename>native.h</filename>.
When a file is used, though,
&SCons; correctly converts the file name
into the &javah; <option>-o</option> option:
</para>
<scons_output example="java_javah_file">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Building RMI Stub and Skeleton Class Files: the &b-RMIC; Builder</title>
<para>
You can generate Remote Method Invocation stubs
by using the &b-link-RMIC; Builder.
The source is a list of directories,
typically returned by a call to the &b-link-Java; Builder,
and the target is an output directory
where the <filename>_Stub.class</filename>
and <filename>_Skel.class</filename> files will
be placed:
</para>
<scons_example name="java_RMIC">
<file name="SConstruct" printme="1">
classes = Java(target = 'classes', source = 'src/pkg/sub')
RMIC(target = 'outdir', source = classes)
</file>
<file name="src/pkg/sub/Example1.java">
package pkg.sub;
public class Example1
{
public static void main(String[] args)
{
}
}
</file>
<file name="src/pkg/sub/Example2.java">
package pkg.sub;
public class Example2
{
public static void main(String[] args)
{
}
}
</file>
</scons_example>
<para>
As it did with the &b-link-JavaH; Builder,
&SCons; remembers the class directory
and passes it as the <option>-classpath</option> option
to &rmic;:
</para>
<scons_output example="java_RMIC">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
This example would generate the files
<filename>outdir/pkg/sub/Example1_Skel.class</filename>,
<filename>outdir/pkg/sub/Example1_Stub.class</filename>,
<filename>outdir/pkg/sub/Example2_Skel.class</filename> and
<filename>outdir/pkg/sub/Example2_Stub.class</filename>.
</para>
</section>
</chapter>
|