Status:

Project status

Pre-release: Not in Maven Central but available for production work.

Latest release: 0.3.1

Summary

The hid4java project supports USB HID devices through a common API which is provided here under the MIT license. The API is very simple but provides great flexibility such as support for feature reports and blocking reads with timeouts. Attach/detach events are provided to allow applications to respond instantly to device availability.

The wiki provides a guide to building the project.

Technologies

• hidapi - Native USB HID library for multiple platforms
• JNA - to remove the need for Java Native Interface (JNI) and greatly simplify the project
• Java 6+ - to remove dependencies on JVMs that have reached end of life

Code example

// Get HID services
hidServices = HidManager.getHidServices();
hidServices.addHidServicesListener(this);

// Provide a list of attached devices
for (HidDevice hidDevice : hidServices.getAttachedHidDevices()) {
  System.out.println(hidDevice);
}

// Open a Bitcoin Trezor device by Vendor ID and Product ID with wildcard serial number
HidDevice trezor = hidServices.getHidDevice(0x534c, 0x01, null);

// Send the Initialise message
byte[] message = new byte[64];
message[0] = 0x3f;
message[1] = 0x23;
message[2] = 0x23;

int val = trezor.write(message, 64, (byte) 0);
if (val != -1) {
  System.out.println("> [" + val + "]");
} else {
  System.err.println(trezor.getLastErrorMessage());
}
    

Getting started

The project uses the standard Maven build process and can be used without having external hardware attached. Just do the usual

cd <project directory>
mvn clean install

and you're good to go. Your next step is to explore the examples (e.g. UsbHidTrezorV1Example). From the command line:

mvn clean compile exec:java -Dexec.mainClass="UsbHidTrezorV1Example"

If you have a Trezor device attached you'll see a "Features" message appear as a big block of hex otherwise it will be just a simple enumeration of attached USB devices. You can plug various devices in and out to see messages.

Use CTRL+C to quit the example.

Frequently asked questions (FAQ)

What platforms do you support ?

If you have a native version of hidapi for your platform then you'll be able to support it.

Pre-compiled versions for Windows (32/64), OS X (10.5+) and Linux (32/64) are provided and you must follow the JNA naming convention when adding new libraries.

Why not just use usb4java ?

The usb4java project, while superb, does not support HID devices on OS X and apparently there are no plans to introduce HID support anytime soon.

You will find that trying to claim the USB device on OS X will fail with permissions problems. If you apply a workaround (such as adding a kernel extension) then it will still fall over just a little later in the process. The bottom line is that you must use hidapi to communicate with HID devices on OS X.

Is this going into Maven Central ?

Yes. There's a bit of general tidying work left to do to take it to a first release but when that's done it will be uploaded to Maven Central.

Can I just copy this code into my project ?

Yes. Perhaps you'd prefer to use

git submodule add https://github.com/gary-rowe/hid4java hid4java 

so that you can keep up to date with changes whilst still fixing the version.

Troubleshooting

The following are known issues and their solutions or workarounds.

I get a SIGSEGV (0xb) when starting up

This shouldn't occur unless you've been changing the code. You have probably got the getFieldOrder list wrong. Use the field list from Class.getFields() to get a suitable order. Another cause is if a Structure has not been initialised and is being deferenced, perhaps in a toString() method.

The hidapi library doesn't load

On startup hid4java will search the classpath looking for a library that matches the machine OS and architecture (e.g. Windows running on AMD64). It uses the JNA naming conventions to do this and will report the expected path if it fails. You can add your own entry under src/main/resources and it should get picked up. Ideally you should raise an issue on the hid4java repo so that the proper library can be put into the project so that others can avoid this problem.

The hidapi library loads but takes a long time on Windows

You have probably terminated the JVM using a kill -9 rather than a clean shutdown. This will have left the HidApi process lock on the DLL still in force and Windows will continuously check to see if it can share it with a new instance. Just detach and re-attach the device to clear it.

I'm seeing spurious attach/detach events occurring on Windows

This was a device enumeration bug in early versions of hid4java. Use 0.3.1 or higher.

My device doesn't work on Linux

Different flavours of Linux require different settings:

Ubuntu

Out of the box Ubuntu classifies HID devices as belonging to root. You can override this rule by creating your own under /etc/udev/rules.d:

sudo gedit /etc/udev/rules.d/99-myhid.rules

Make the content of this file as below (using your own discovered hex values for idProduct and idVendor):

# My HID device
ATTRS{idProduct}=="0001", ATTRS{idVendor}=="abcd", MODE="0660", GROUP="plugdev"

Save and exit from root, then unplug and replug your device. The rules should take effect immediately. If they're still not running it may that you're not a member of the plugdev group. You can fix this as follows (assuming that plugdev is not present on your system):

sudo addgroup plugdev
sudo addgroup yourusername plugdev

Slackware

Edit the USB udev rules /etc/udev/rules.d as follows:

MODE="0666", GROUP="dialout"

Closing notes

All trademarks and copyrights are acknowledged.

Many thanks to victorix who provided the basis for this library. Please see the inspiration on the mbed.org site.