This is Java API extension to yad2xx. 16 GPIO pins can be controlled as input or output.

// configure an I2C instance
I2C device;
// create MCP23017 instance
MCP23017 mcp = new MCP23017(device);
// register some pins as output
mcp.setupOutput(Pin.GPIO_B_0);
mcp.setupOutput(Pin.GPIO_B_2);
mcp.setupOutput(Pin.GPIO_B_1);
mcp.setupOutput(Pin.GPIO_B_3);
mcp.setupOutput(Pin.GPIO_B_4);
mcp.setupOutput(Pin.GPIO_B_5);
// register some pins as input
mcp.setupInput(Pin.GPIO_A_6);
mcp.setupInput(Pin.GPIO_A_7);
// set an output pin to ON
mcp.on(Pin.GPIO_B_0);
// check if input on pin
if (mcp.isSet(Pin.GPIO_A_6)) {
  ...
}

This project is using the yad2xx library released under LGPL3. The dynamic linking is done using Maven dependency mechanism. To change the linking to a different version of the library just change the dependency. A copy of the library binary and license is available in the lib folder. A source artifact has not been provided by the publisher of the library. You can find the source code on the SourceForge project page of yad2xx.

The datasheet of MCP23017 can be found in the doc folder.