# JPL 3.x installation

First check that the prerequisites (see the home page) are satisfied (you have SWI-Prolog 5.2.0 or later, a Java 2 SDK, and a compatible operating system).

Unzip jpl.zip somewhere safe (maybe into the \pl folder of your SWI-Prolog installation): it creates a folder \jpl which you should retain.

Inspect your new \jpl folder: it should contain

    jpl
     +--- examples
     |     +--- Exceptions
     |     +--- Exceptions2
     |     +--- Family
     |     +--- Test
     |     +--- Test2
     |     +--- Time
     |     +--- Zahed
     |     +--- (and maybe more...)
     |
     +--- docs  (HTML files in here are accessible via links from the home page)
     |
     +--- src
     |     +--- c
     |     |    +--- build.bat  (Windows script to recompile jpl.c to jpl.dll)
     |     |    +--- build.sh  (Linux script to recompile jpl.c to libjpl.so)
     |     +--- java
     |
     +--- jpl.dll  (a native library - for Windows in this case)
     |
     +--- jpl.jar  (a Java library)
     |
     +--- jpl.pl  (a Prolog library)
     |
     +--- README.html  (JPL's documentation "home page")

Put the three library files (jpl.dll, jpl.jar and jpl.pl) where each can be found:

- jpl.dll must be found by the Windows kernel, and can go in any folder on your PATH; perhaps %SWI_HOME_DIR%\bin or your Windows system folder
- jpl.jar must be found by any Java VMs (and compilers) used with JPL; one possibility is to put it on your global CLASSPATH
- jpl.pl is a Prolog source module, and must be found by any SWI-Prolog engines used with JPL: I suggest putting it in %SWI_HOME_DIR%\library and then invoking make_library_index/1 on that folder (see a SWI-Prolog manual for details) so that the autoloader can find it.

For SWI-Prolog to initialise (or make the first call) to JPL, it is necessary that a folder containing the JVMlibrary (jvm.dll) is on your PATH; if you are using a recent Sun JRE, look for a PATH entry of the form C:\jdk1.3.1_01\jre\bin\hotspot; or C:\jdk1.3.1_01\jre\bin\client;
If your applications start in Java, and then call SWI-Prolog, it is necessary that the SWI-Prolog library libpl.dll is in a folder on the PATH
Try the Java example in

    examples/java/Versions

or the Prolog example in

    examples/prolog/jpl_versions_demo.pl

to confirm that all three libraries are installed and compatible.

### Installation troubleshooting

If the example programs don't run successfully, look carefully at any error messages; they typically indicate where the problem lies. Then check the installation instruction s and prerequisites carefully.

- If you get a message about

    ... jpl.dll ... Access is denied ...

then you may have lost execute permission on jpl.dll (please consult local Windows expertise if you don't know how to correct this).

- If jpl_examples/0 complains that

The dynamic link library jvm.dll could not be found in the specified path
then you should locate jvm.dll within the Java runtime which you intend to use, and ensure that its directory is within the PATH.

- if the Java examples (e.g. jpl\examples\Exception\run.bat) complain that

The name specified is not recognized as an internal or external command, operable program or batch file.
then there is no Java executable java.exe in any folder on your PATH: you should have a PATH entry such as C:\jdk1.3.1_01\bin;

- if the Java examples complain that

The dynamic link library libpl.dll could not be found in the specified path
or
Exception in thread "main" java.lang.UnsatisfiedLinkError: C:\paul\bin\jpl.dll: Can't find dependent libraries
then there is no SWI-Prolog library libpl.dll in any folder on your PATH: you should have a PATH entry such as C:\Program Files\pl\bin