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font
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lib
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README.md
README.md
 
 
display.sh
display.sh
 
 
i2c_ssd1306_java_awt.dart
i2c_ssd1306_java_awt.dart
 
 
jvm_bridge.c
jvm_bridge.c
 
 

README.md

Example for a Dart-Java-Bridge

This example uses the Java AWT class to generate graphics for the OLED SSD1306.

The demo displays two images: an emoji and a sine curve, both created using a BSH (Java BeanShell) script.

📋 Prerequisites

  • Raspberry Pi or compatible SBC with I2C support
  • SSD1306 OLED display connected via I2C
  • OpenJDK 17 or higher
  • Dart SDK installed
  • dart_periphery package

📖 Steps to Start the Demo (Tested on Raspberry OS and Armbian)

Step 1. Install OpenJDK:

sudo apt-get install openjdk-17-jdk

Armbian supports higher JDK versions e.g.

sudo apt install openjdk-21-jre-headless

Step 2. Set the JAVA_HOME environment variable:

Try autodetection:

export JAVA_HOME=$(update-java-alternatives -l | awk '{print $3}')
echo $JAVA_HOME

Step 3. Compile the Java code, including BeanShell support:

javac -cp ./lib/bsh-2.0b4.jar at/flutterdev/EmojiBMPGenerator.java

Step 4. Compile the C code as a shared library:

gcc -shared -o libjvmbridge.so -fPIC jvm_bridge.c  -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" -L"$JAVA_HOME/lib/server" -ljvm

Step 5. Set the LD_LIBRARY_PATH to include the JVM library and libjvmbridge.so

export LD_LIBRARY_PATH=$JAVA_HOME/lib/server:.

Step 6. Start the program:

dart i2c_ssd1306_java_awt.dart

📣 Additional Information for Development and Testing

Test the Java layer - main method with test code

java -cp ./lib/bsh-2.0b4.jar at/flutterdev/EmojiBMPGenerator.java

Test the C layer - main method with test code

macOS:

gcc -o calljava -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/darwin" jvm_bridge.c -L"$JAVA_HOME/lib/server" -ljvm

Linux:

gcc -o calljava -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" jvm_bridge.c -L"$JAVA_HOME/lib/server" -ljvm

Additional step for macOS to set the RPATH

install_name_tool -add_rpath $JAVA_HOME/lib/server/ ./calljava

Test the Dart layer

On macOS, a Dart program invoking the JVM may encounter a missing RPATH issue. Since you cannot apply install_name_tool directly to a Dart source file, you need to apply it to the compiled executable version of the Dart program:

dart compile exe test.dart
install_name_tool -add_rpath $JAVA_HOME/lib/server/ test