Java support

Javac is one of the few compilers that behaves very badly:

  1. it outputs files where it wants to (-d is only for the package root)
  2. it recompiles files silently behind your back
  3. it outputs an undefined amount of files (inner classes)

Remember that the compilation can be performed using Jython[1] rather than regular Python. Instead of running one of the following commands:

./waf configure
python waf configure

You would have to run:

java -jar /path/to/jython.jar waf configure



Load the “java” tool.

def configure(conf):

Java tools will be autodetected and eventually, if present, the quite standard JAVA_HOME environment variable will be used. The also standard CLASSPATH variable is used for library searching.

In configuration phase checks can be done on the system environment, for example to check if a class is known in the classpath:


or if the system supports JNI applications building:


The java tool supports compiling java code, creating jar files and creating javadoc documentation. This can be either done separately or together in a single definition. For example to manage them separately:

bld(features  = 'javac',
        srcdir    = 'src',
        compat    = '1.7',
        use       = 'animals',
        name      = 'cats-src',

bld(features  = 'jar',
        basedir   = '.',
        destfile  = '../cats.jar',
        name      = 'cats',
        use       = 'cats-src'

Or together by defining all the needed attributes:

bld(features   = 'javac jar javadoc',
        srcdir     = 'src/',  # folder containing the sources to compile
        outdir     = 'src',   # folder where to output the classes (in the build directory)
        compat     = '1.6',   # java compatibility version number
        classpath  = ['.', '..'],

        # jar
        basedir    = 'src', # folder containing the classes and other files to package (must match outdir)
        destfile   = 'foo.jar', # do not put the destfile in the folder of the java classes!
        use        = 'NNN',
        jaropts    = ['-C', 'default/src/', '.'], # can be used to give files
        manifest   = 'src/', # Manifest file to include

        # javadoc
        javadoc_package = ['com.meow' , '', ''],
        javadoc_output  = 'javadoc',

External jar dependencies can be mapped to a standard waf “use” dependency by setting an environment variable with a CLASSPATH prefix in the configuration, for example:

conf.env.CLASSPATH_NNN = ['aaaa.jar', 'bbbb.jar']

and then NNN can be freely used in rules as:

use        = 'NNN',

In the java tool the dependencies via use are not transitive by default, as this necessity depends on the code. To enable recursive dependency scanning use on a specific rule:

recurse_use = True

Or build-wise by setting RECURSE_JAVA:

bld.env.RECURSE_JAVA = True

Unit tests can be integrated in the waf unit test environment using the javatest extra.


Task generator method

Create a javac task for compiling .java files. There can be only one javac task by task generator.

waflib.Tools.javaw.java_use_rec(self, name, **kw)[source]

Task generator method

Processes recursively the use attribute for each referred java compilation


Task generator method

Processes the use attribute referring to other java compilations


Task generator method

Sets the CLASSPATH value on the javac task previously created.


Task generator method

Creates a jar task (one maximum per task generator)


Task generator method

Processes the use attribute to set the build order on the tasks created by another task generator.

class waflib.Tools.javaw.JTask(*k, **kw)[source]

Bases: waflib.Task.Task

Base class for java and jar tasks; provides functionality to run long commands


Splits a list of process commands into the executable part and its list of arguments

Returns:a tuple containing the executable first and then the rest of arguments
Return type:tuple
class waflib.Tools.javaw.jar_create(*k, **kw)[source]

Bases: waflib.Tools.javaw.JTask

Creates a jar file

color = 'GREEN'

Wait for dependent tasks to be executed, then read the files to update the list of inputs.

hcode = b'${JAR} ${JARCREATE} ${TGT} ${JAROPTS}'
orig_run_str = '${JAR} ${JARCREATE} ${TGT} ${JAROPTS}'
vars = ['JAR', 'JARCREATE', 'JAROPTS']
class waflib.Tools.javaw.javac(*k, **kw)[source]

Bases: waflib.Tools.javaw.JTask

Compiles java files

color = 'BLUE'

The javac task will be executed again if the variables CLASSPATH, JAVACFLAGS, JAVAC or OUTDIR change.


Identify java tasks by input&output folder


Waits for dependent tasks to be complete, then read the file system to find the input nodes.


List class files created

hcode = b'${JAVAC} -classpath ${CLASSPATH} -d ${OUTDIR} ${JAVACFLAGS} ${SRC}'
orig_run_str = '${JAVAC} -classpath ${CLASSPATH} -d ${OUTDIR} ${JAVACFLAGS} ${SRC}'

Task generator method

Creates a javadoc task (feature ‘javadoc’)

class waflib.Tools.javaw.javadoc(*k, **kw)[source]

Bases: waflib.Task.Task

Builds java documentation

color = 'BLUE'

Update the cache files (executed by threads). Override in subclasses.

hcode = b'\tdef run(self):\n\t\tenv = self.env\n\t\tbld = self.generator.bld\n\t\twd = bld.bldnode\n\n\t\t#add src node + bld node (for generated java code)\n\t\tsrcpath = self.generator.path.abspath() + os.sep + self.generator.srcdir\n\t\tsrcpath += os.pathsep\n\t\tsrcpath += self.generator.path.get_bld().abspath() + os.sep + self.generator.srcdir\n\n\t\tclasspath = env.CLASSPATH\n\t\tclasspath += os.pathsep\n\t\tclasspath += os.pathsep.join(self.classpath)\n\t\tclasspath = "".join(classpath)\n\n\t\tself.last_cmd = lst = []\n\t\tlst.extend(Utils.to_list(env.JAVADOC))\n\t\tlst.extend([\'-d\', self.generator.javadoc_output.abspath()])\n\t\tlst.extend([\'-sourcepath\', srcpath])\n\t\tlst.extend([\'-classpath\', classpath])\n\t\tlst.extend([\'-subpackages\'])\n\t\tlst.extend(self.generator.javadoc_package)\n\t\tlst = [x for x in lst if x]\n\n\t\tself.generator.bld.cmd_and_log(lst, cwd=wd, env=env.env or None, quiet=0)\n'

Detects the javac, java and jar programs

waflib.Tools.javaw.check_java_class(self, classname, with_classpath=None)[source]

Configuration Method bound to waflib.Configure.ConfigurationContext

Checks if the specified java class exists

  • classname (string) – class to check, like java.util.HashMap
  • with_classpath (string) – additional classpath to give

Decorator: attach new configuration functions to waflib.Build.BuildContext and waflib.Configure.ConfigurationContext. The methods bound will accept a parameter named ‘mandatory’ to disable the configuration errors:

def configure(conf):
        conf.find_program('abc', mandatory=False)
Parameters:f (function) – method to bind

Decorator that registers a task generator method that will be executed when the object attribute feature contains the corresponding key(s):

from waflib.Task import feature
def myfunction(self):
        print('that is my feature!')
def build(bld):
Parameters:k (list of string) – feature names

Decorator that registera task generator method which will be executed before the functions of given name(s):

from waflib.TaskGen import feature, before
def fun1(self):
        print('feature 1!')
def fun2(self):
        print('feature 2!')
def build(bld):
Parameters:k (list of string) – method names

Decorator that registers a task generator method which will be executed after the functions of given name(s):

from waflib.TaskGen import feature, after
def fun1(self):
        print('feature 1!')
def fun2(self):
        print('feature 2!')
def build(bld):
Parameters:k (list of string) – method names

Decorator that registers method as a task generator method. The function must accept a task generator as first parameter:

from waflib.TaskGen import taskgen_method
def mymethod(self):
Parameters:func (function) – task generator method to add
Return type:function

Configuration Method bound to waflib.Configure.ConfigurationContext

Checks for jni headers and libraries. On success the conf.env variables xxx_JAVA are added for use in C/C++ targets:

def options(opt):

def configure(conf):
        conf.load('compiler_c java')

def build(bld):
        bld.shlib(source='a.c', target='app', use='JAVA')

Features defined in this module: