One of the "cool" features of Java ME Embedded 8 is the Device I/O (DIO) API. With DIO, you can write Java code to take advantage of the GPIO header on the Raspberry Pi, and connect LED's, switches, I2C and SPI devices, and serial devices that use a UART. This opens up the world of the Internet of Things to Java developers, and for less than $40 US!

Java SE, both 7 and 8 are also available for the Raspberry Pi (ARM 6 architecture), and if you want to explore Java SE Embedded, and play with profiles, you can do that too. But what about Java EE and Web Services? How do I access devices using servlets and web services?

The answer is by combining two technologies. Recently, the Device I/O API has been under development as an Open JDK project - creating a standalone way to access the GPIO header using exactly the same API that makes Java ME Embedded so special. This allows developers to write DIO code outside of a Java ME Embedded VM.

OpenJDK Device I/O is a third-party library which leverages standard Java ME Device I/O APIs to Java SE.

To learn more:

1 Install JDK 1.8

Ensure JDK 1.8 is installed

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$ java -version
java version "1.8.0_65"
Java(TM) SE Runtime Environment (build 1.8.0_65-b17)
Java HotSpot(TM) Client VM (build 25.65-b01, mixed mode)

If not installed you can install it by doing:

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$ sudo apt-get update
$ sudo apt-get install oracle-java8-jdk

2 Install JDK IO

Next, download the JDK DIO developer code. This library has device providers for JDK Device I/O v1.0 (in Mercurial master repository) and v1.1 Mercurial (in dev repository).

  • Install mercurial
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    $ sudo apt-get -y install mercurial
  • Install zip
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    $ sudo apt-get install zip unzip
  • Create directory deviceio
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    $ mkdir deviceio
$ cd deviceio
  • Clone JDK dio 1.0 (master repository) or 1.1 (dev repository)
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    $ hg clone http://hg.openjdk.java.net/dio/master/
    destination directory: master
requesting all changes
adding changesets
adding manifests
adding file changes
added 276 changesets with 1579 changes to 314 files
updating to branch default
291 files updated, 0 files merged, 0 files removed, 0 files unresolved
  • Change to deviceio cloned directory master
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    $ cd master
$ ls -l
    -rw-r--r-- 1 pi pi  2516 Oct 23 17:51 Javadoc.gmk
-rw-r--r-- 1 pi pi 19264 Oct 23 17:51 LICENSE
-rw-r--r-- 1 pi pi 11187 Oct 23 17:51 Makefile
-rw-r--r-- 1 pi pi   940 Oct 23 17:51 README
-rw-r--r-- 1 pi pi  1294 Oct 23 17:51 README_Tests
drwxr-xr-x 2 pi pi  4096 Oct 23 17:51 config
drwxr-xr-x 2 pi pi  4096 Oct 23 17:51 jrecreate
drwxr-xr-x 4 pi pi  4096 Oct 23 17:51 samples
drwxr-xr-x 5 pi pi  4096 Oct 23 17:51 src
drwxr-xr-x 5 pi pi  4096 Oct 23 17:51 test
  • Determine where Java is installed
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    $ ls /usr/lib/jvm/
    jdk-8-oracle-arm32-vfp-hflt
  • Setup JAVA_HOME to point the installed java
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    $ export JAVA_HOME=/usr/lib/jvm/jdk-8-oracle-arm32-vfp-hflt
$ export PI_TOOLS=/usr
$ make osgi
    Creating output directories
Compiling Java source files to /home/pi/dio/master/build/jar/dio.jar
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
Compiling src/se/native/com/oracle/dio/dio_common.cpp
Compiling src/se/native/com/oracle/dio/dio_exceptions.cpp
Compiling src/se/native/com/oracle/dio/uart/impl/jni_signal_dispatcher.cpp
Compiling src/se/native/com/oracle/dio/uart/impl/jni_modem.cpp
Compiling src/se/native/com/oracle/dio/uart/impl/jni_uart.cpp
Compiling src/se/native/com/oracle/dio/i2cbus/impl/jni_i2c.cpp
Compiling src/se/native/com/oracle/dio/gpio/impl/jni_gpio.cpp
Compiling src/se/native/com/oracle/dio/dio_nio.cpp
...
  • Now copy the libraries in Raspberry PI
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    $ cp build/deviceio/lib/ext/dio.jar dio-1.0.jar
$ sudo cp build/deviceio/lib/ext/dio.jar $JAVA_HOME/jre/lib/ext/.
$ sudo cp build/deviceio/lib/arm/libdio.so $JAVA_HOME/jre/lib/arm/.
  • Trasnfer dio library to a workstation if you are using cross development. In the example we transfer from a pi located at address 192.168.1.47 to our local workstation:
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    $ scp pi@192.168.1.47:/home/pi/dio/master/dio-1.0.jar .