Java Plugin (for Choco)

The Java plugin of Ibex allows to use Ibex with Choco, for solving mixed integer-continuous CSP (constraint satisfaction problems).

Important

Starting release 2.9 of Ibex, the java interface will no longer be a separate plugin but integrated in the kernel. You just have to run cmake with -DBUILD_JAVA_INTERFACE=ON option. The installation procedure below is only valid for release before 2.8.

The installation of the plugin will generate, in addition to the Ibex library, the libibex-java library that contains the glue code between C++ and Java.

Note

Under Windows, Ibex is compiled as a 32-bit library although the platform is 64 bits (this is mainly because the MinGW environment is 32-bits). Hence, Java will fail in loading Ibex unless you have a 32-bits JVM. The following instructions must be typed in the shell of MinGW.

Linux/MacOS

• Install ibex following instructions here

• Uncompress the archive ibex-2.8.9.tar.gz in some Ibex folder:: ~/Ibex/$ tar xvfz ibex-2.8.9.tar.gz

• Download the last release of the ibex-java plugin (1.0.0)

• Uncompress the archive ibex-java-1.0.0.tar.gz

• Rename the folder ibex-java-1.0.0 to ibex-java and place this folder under ~/Ibex/ibex-2.8.9/plugins

• Set the environment variable JAVA_HOME. Typical paths are /Library/Java/Home (MacOS) or /usr/lib/jvm/java-7-openjdk-i38 (Linux). Example:: ~/Ibex/$ export JAVA_HOME=/Library/Java/Home

• Then configure and install Ibex as follows::

  ~/Ibex/$ cd ibex-2.8.9
  ~/Ibex/ibex-2.8.9/$ ./waf configure [...] --enable-shared --with-jni --java-package-name=org.chocosolver.solver.constraints.real
  ~/Ibex/ibex-2.8.9/$ ./waf install
  

  Note: the --enable-shared option is mandatory.

Windows

• Install ibex following instructions here

• Open a MinGW prompt window.

• Uncompress the archive ibex-2.8.9.tar.gz in some Ibex folder:: ~/Ibex/$ tar xvfz ibex-2.8.9.tar.gz

• Download the last release of the ibex-java plugin (1.0.0)

• Uncompress the archive ibex-java-1.0.0.tar.gz

• Rename the folder ibex-java-1.0.0 to ibex-java and place this folder under ~/Ibex/ibex-2.8.9/plugins

• Set the environment variable JAVA_HOME to the home directory of the 32 bits JDK. The variable must be set in Linux-style (don't use backslash ("\") as separator), e.g.::

    ~/Ibex/$ export JAVA_HOME=/c/Java/jdk1.7.1_17
  

• Update the path as follows:: ~/Ibex/$ set PATH=%PATH%;[prefix]\lib;C:\MinGW\bin where [prefix] is the path specified via --prefix

  Warning: The path must not contain white spaces, like ”/c/Program Files/...”. Create a symbolik link of your Java directory if necessary.

• Then configure Ibex as follows::

    ~/Ibex/$ cd ibex-2.8.9
    ~/Ibex/ibex-2.8.9/$ ./waf configure [...] --enable-shared --with-jni --java-package-name=org.chocosolver.solver.constraints.real
    ~/Ibex/ibex-2.8.9/$ ./waf install
  

  Note: the --enable-shared option is mandatory.

Configuration options

The IbexOpt plugin supports the following options (to be used with waf configure) :

Option	Description
--with-jni	Activate the Java plugin.
--java-package-name=PACKAGE_NAME	The plugin will create the PACKAGE_NAME.jar file. This file is put into the [prefix]/share/java where [prefix] is /usr/local by default or whatever path specified via --prefix.

Troubleshooting

UnsatisfiedLinkError with Choco

When running the “CycloHexan” example from Choco using Ibex, the following error appears::

Exception in thread "main" java.lang.UnsatisfiedLinkError: org.chocosolver.solver.constraints.real.Ibex.add_ctr(ILjava/lang/String;I)V
at org.chocosolver.solver.constraints.real.Ibex.add_ctr(Native Method)
at org.chocosolver.solver.constraint.propagators.real.RealPropagator.<init>(RealPropagator.java:77)
at org.chocosolver.solver.constraints.real.RealConstraint.addFunction(RealConstraint.java:82)
at samples.real.CycloHexan.buildModel(CycloHexan.java:87)
at samples.AbstractProblem.execute(AbstractProblem.java:130)
at samples.real.CycloHexan.main(CycloHexan.java:134)

Solution: You probably did not set the Java package properly. The java package of the Ibex class in Choco is org.chocosolver.solver.constraints.real, try::

./waf configure [....] --java-package-name=org.chocosolver.solver.constraints.real

JAVA_HOME does not seem to be set properly

I get this message when running waf configure.

Solution: The JAVA_HOME must be the path of the JDK and contain a subdirectoy include which, in turn, contains the jni.h header file (for Java versions <10). On MacOS this path can be /Library/Java/JavaVirtualMachines/jdkXXXX.jdk/Contents/Home.