Accessing Java¶

In addition to the common Script API utilities, Yamcs Studio allows bridged access within scripts to entire Java packages.

Yamcs Studio uses the Eclipse RCP framework, so for example, here we make use of JFace to open a message dialog:

var MessageDialog = Java.type("org.eclipse.jface.dialogs.MessageDialog");
MessageDialog.openInformation(
    null, "Attention", "I was triggered by a script");

If you go in this direction, at some point it may make more sense to extend or fork Yamcs Studio at a Java level, rather than using display scripting.

Note further that such scripts are not compatible when rendering your OPI displays via the Yamcs web interface.

Full documentation of Java and Eclipse APIs is well outside of scope of this document, so we leave this topic with a complex example that uses Eclipse SWT and Java I/O. The script logic is as follows:

Download a random image from Internet.
Save this image to a file within the workspace.
Create or reuse a standalone window to display the image.

var BufferedInputStream = Java.type("java.io.BufferedInputStream");
var Display = Java.type("org.eclipse.swt.widgets.Display");
var FileOutputStream = Java.type("java.io.FileOutputStream");
var File = Java.type("java.io.File");
var Image = Java.type("org.eclipse.swt.graphics.Image");
var ImageData = Java.type("org.eclipse.swt.graphics.ImageData");
var Label = Java.type("org.eclipse.swt.widgets.Label");
var Shell = Java.type("org.eclipse.swt.widgets.Shell");
var SWT = Java.type("org.eclipse.swt.SWT");
var URL = Java.type("java.net.URL");

function downloadNewImage() {
  var cacheDir = FileUtil.workspacePathToSysPath("/") + "/images_cache/";
  new File(cacheDir).mkdir();
  var filename = cacheDir + "cache" + Date.now() + ".jpg";

  var urlIn = new BufferedInputStream(
    new URL("https://source.unsplash.com/random").openStream()
  );
  var fileOut = new FileOutputStream(filename);
  var ByteArray = Java.type("byte[]");
  var buf = new ByteArray(1024);
  var n;
  while ((n = urlIn.read(buf, 0, 1024)) != -1) {
    fileOut.write(buf, 0, n);
  }
  urlIn.close();
  fileOut.close();

  return filename;
}

function getShell(display, origin) {
  var shells = display.getShells();
  for (var i = 0; i < shells.length; i++) {
    if (shells[i].getData("origin") == origin) {
      return shells[i];
    }
  }
  var newShell = new Shell(display);
  newShell.setData("origin", origin);
  newShell.setData("label", new Label(newShell, SWT.BORDER));
  return newShell;
}

var filename = downloadNewImage();
var display = Display.getCurrent();
var imgData = new ImageData(filename);
var image = new Image(display, imgData);
var shell = getShell(display, "test-script-shell");
var clientArea = shell.getClientArea();
var label = shell.getData("label");
label.setLocation(clientArea.x, clientArea.y);
label.setImage(image);
label.pack();
shell.pack();
shell.open();