NAME

       md_src_plugins_jni_READMEREADME
        -

       • infos = Information about the jni plugin is in keys below

       • infos/author = Name name@libelektra.org

       • infos/licence = BSD

       • infos/needs =

       • infos/provides =

       • infos/placements =

       • infos/description =

Generic Java plugin

   Introduction
       Allows you to write plugins in java.

       Needs Java 8 or later. While the plugin internally uses JNI, the Java binding for your
       java-plugin may use something different, e.g. JNA. The requirements for the java bindings
       are:

       • needs to have the classes elektra/Key and elektra/KeySet with

         • an constructor that takes a C-Pointer as long (J)

         • an method 'release' that gives up ownership (set internal pointer to NULL)

       The java plugin itself needs to have following methods:

       • constructor without arguments (e.g. default constructor)

       • open with argument elektra/KeySet (the plugin's conf) and elektra/Key

       • close with argument elektra/Key

       • get with arguments elektra/KeySet and elektra/Key

       • set with arguments elektra/KeySet and elektra/Key

       • error with arguments elektra/KeySet and elektra/Key

   Installation
       Please install java8 as package, e.g. for debian and then let cmake actually find jdk8:

       cd /usr/lib/jvm/ && sudo rm -f default-java && sudo ln -s java-8-oracle default-java

       and for the runtime, create the file /etc/ld.so.conf.d/java-8-oracle.conf with the content
       (for amd64):

       /usr/lib/jvm/default-java/jre/lib/amd64
       /usr/lib/jvm/default-java/lib/amd64
       /usr/lib/jvm/default-java/jre/lib/amd64/server

       and run:

       sudo ldconfig

       Then enable the plugin using:

       cmake -DPLUGINS="...;jni" /path/to/libelektra

       Running

       kdb-full

       should work then, if you get one of these:

       kdb-full: error while loading shared libraries: libmawt.so: cannot open shared object file: No such file or directory
       kdb-full: error while loading shared libraries: libjawt.so: cannot open shared object file: No such file or directory

       You missed one of the ldconfig steps.

   Plugin Config
       You need to pass :

       • classname the classname to use as plugin, e.g. elektra/plugin/Echo

       • classpath the classpath where to find JNA, the package elektra and other classes needed

       Additionally, you can set:

       • option allows you to pass a option to the jvm, default: -verbose:gc,class,jni

       • ignore allows you to ignore broken options, default: false

       • print allows you to print java exceptions for debugging purposes

       E.g.

       kdb info -c classname=elektra/plugin/PropertiesStorage,classpath=.:/usr/share/java/jna.jar:/usr/lib/java:/path/to/libelektra/src/bindings/jna,print= jni
       kdb check -c classname=elektra/plugin/PropertiesStorage,classpath=.:/usr/share/java/jna.jar:/usr/lib/java:/path/to/libelektra/src/bindings/jna,print= jni
       kdb mount -c classname=elektra/plugin/PropertiesStorage,classpath=.:/usr/share/java/jna.jar:/usr/lib/java:/path/to/src/bindings/jna,print= file.properties /jni jni classname=elektra/plugin/PropertiesStorage,classpath=.:/usr/share/java/jna.jar:/usr/lib/java:/path/to/libelektra/src/bindings/jna,print=

       Or if .jar is already installed:

       bin/kdb mount -c classname=elektra/plugin/PropertiesStorage,classpath=.:/usr/share/java/jna.jar:/usr/share/java/elektra.jar,print= file.properties /jni jni classname=elektra/plugin/PropertiesStorage,classpath=.:/usr/share/java/jna.jar:/usr/share/java/elektra.jar,print=

       Additionally, the java implementation can request any other additional configuration, read
       about it below in the section (specific java plugin). If you are reading this page on
       github, you won't see it, because the plugins dynamically append text after the end of
       this page.

   Development
       To know how the methods of your class are called, use:

       javap -s YourClass

       Also explained here

       JNI Functions Invocation

   Issues
       • In Debian Wheezy you cannot use openjdk: you get a linker error because of some missing
         private SUN symbols. Maybe just the cmake mechanism to find java is broken.

       • Only a single java plugin can be loaded

       • when this plugin is enabled, valgrind detects memory problems even if the plugin is not
         mounted.

Specific Java Plugin