README: Document how to build the Java plugin.

diff --git a/README b/README
index 755704d..a1bf5ff 100644 (file)
--- a/README
+++ b/README
@@ -104,6 +104,10 @@ Features
     - irq
       IRQ counters: Frequency in which certain interrupts occur.
 
+    - java
+      Integrates a `Java Virtual Machine' (JVM) to execute plugins in Java
+      bytecode. See “Configuring with libjvm” below.
+
     - load
       System load average over the last 1, 5 and 15 minutes.
 
@@ -436,6 +440,11 @@ Prerequisites
     For querying iptables counters.
     <http://netfilter.org/>
 
+  * libjvm (optional)
+    Library that encapsulates the `Java Virtual Machine' (JVM). This library is
+    used by the Java plugin to execute Java bytecode. See “Configuring with
+    libjvm” below.
+
   * libmysqlclient (optional)
     Unsurprisingly used by the `mysql' plugin.
     <http://dev.mysql.com/>
@@ -534,6 +543,42 @@ Configuring / Compiling / Installing
   prefixed to all installation directories. This might be useful when creating
   packages for collectd.
 
+Configuring with libjvm
+-----------------------
+
+  To determine the location of the required files of a Java installation is not
+  an easy task, because the locations vary with your kernel (Linux, SunOS, …)
+  and with your architecture (x86, SPARC, …) and there is no ‘java-config’
+  script we could use. Configuration of the JVM library is therefore a bit
+  tricky.
+
+  The easiest way to use the `--with-java=$JAVA_HOME' option, where
+  `$JAVA_HOME' is usually something like:
+    /usr/lib/jvm/java-1.5.0-sun-1.5.0.14
+
+  The configure script will then use find(1) to look for the following files:
+
+    - jni.h
+    - jni_md.h
+    - libjvm.so
+
+  If found, appropriate CPP-flags and LD-flags are set and the following
+  library checks succeed.
+
+  If this doesn't work for you, you have the possibility to specify CPP-flags,
+  C-flags and LD-flags for the ‘Java’ plugin by hand, using the following three
+  (environment) variables:
+
+    - JAVA_CPPFLAGS
+    - JAVA_CFLAGS
+    - JAVA_LDFLAGS
+
+  For example (shortened for demonstration purposes):
+
+    ./configure JAVA_CPPFLAGS="-I$JAVA_HOME/include -I$JAVA_HOME/include/linux"
+
+  Adding "-ljvm" to the JAVA_LDFLAGS is done automatically, you don't have to
+  do that.
 
 Crosscompiling
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