是否可以注册一个Java程序完全加载时触发的javascript事件？

Question

I have a web application that uses java applet defined in a <applet> tag. Is it possible to add a javascript event that is triggered after the applet is fully loaded? This is some initialization javascript that is dependent on that the applet is fully loaded and valid.

Answer 1

javascript invoking is rather simple:

Your init() method can include the jsObject declaration and javascript invoking:

@Override
public void init() {
// some code
  JSObject jsObject = JSObject.getWindow(this);
  jsObject.eval("your javascript");

}

Answer 2

If you don't have source code control over the applet, you can poll for the applet to be loaded before calling methods on it. Here is a utility function I wrote that does just that:

/* Attempt to load the applet up to "X" times with a delay. If it succeeds, then execute the callback function. */
function WaitForAppletLoad(applet_id, attempts, delay, onSuccessCallback, onFailCallback) {
    //Test
    var to = typeof (document.getElementById(applet_id));
    if (to == 'function' || to == 'object') {
        onSuccessCallback(); //Go do it.
        return true;
    } else {
        if (attempts == 0) {
            onFailCallback();
            return false;
        } else {
            //Put it back in the hopper.
            setTimeout(function () {
                WaitForAppletLoad(applet_id, --attempts, delay, onSuccessCallback, onFailCallback);
            }, delay);
        }
    }
}

Call it like this:

WaitForAppletLoad("fileapplet", 10, 2000, function () {
        BuildTree("c:/");
    }, function () {
        alert("Sorry, unable to load the local file browser.");
    });

Answer 3

You have an initializer function (i think it is run) in java applet. From there you can call a javascript in the web page after initialization work. To work you must add the MAYSCRIPT attribute to your applet definition

<applet id="someId" code="JavaApplet.class" codebase="/foo" archive="Applet.jar" MAYSCRIPT>
</applet>

Code example to invoke a JavaScript:

public String invokeJavaScript(Object caller, String cmd) throws TiNT4Exception {
    printDebug(2, "Start JavaScript >>" + cmd + "<<");
    try {
      // declare variables
      Method getw = null;
      Method eval = null;
      Object jswin = null;

      // create new instance of class netscape.javascript.JSObject
      Class c = Class.forName("netscape.javascript.JSObject"); // , true, this.getClass().getClassLoader()); // does it in IE too

      // evaluate methods
      Method ms[] = c.getMethods();
      for (int i = 0; i < ms.length; i ++) {
        if (ms[i].getName().compareTo("getWindow") == 0) { getw = ms[i]; }
        else if (ms[i].getName().compareTo("eval") == 0) { eval = ms[i]; }
      } // for every method

      printDebug(3, "start invokings");
      Object a[] = new Object[1];
      a[0] = caller;
      jswin = getw.invoke(c, a);
      a[0] = cmd;
      Object result = eval.invoke(jswin, a);

      if (result == null) {
        printDebug(3, "no return value from invokeJavaScript");
        return "";
      }

      if (result instanceof String) {
        return (String)result;
      } else {
        return result.toString();
      }
    } catch (InvocationTargetException ite) {
      throw new TiNT4Exception(ite.getTargetException() + "");
    } catch (Exception e) {
      throw new TiNT4Exception(e + "");
    }
  } // invokeJavaScript

Answer 4

You can use the param tag to pass the name of a JS function into your applet:

<applet id="myapplet" code="JavaApplet.class" codebase="/foo"
        archive="Applet.jar" MAYSCRIPT>
  <param name="applet_ready_callback" value="myJSfunction"/>
</applet>

In your applet, get the value of the param and call the function when ready:

@Override
public void init() {
  String jsCallbackName = getParameter("applet_ready_callback");
  JSObject jsObject = JSObject.getWindow(this);
  jsObject.eval(jsCallbackName + "()");
}

Answer 5

I used another way to call a JavaScript function from an applet.

try {
    getAppletContext().showDocument(new URL("javascript:appletLoaded()"));
} catch (MalformedURLException e) {
    System.err.println("Failed to call JavaScript function appletLoaded()");
}

...must be called in the applet class which extends Applet or JApplet. I called the JavaScript function at the end of my start() method.

Answer 6

It is possible with Java 7 SE. You can register onLoad() event or just poll status , see Handling Initialization Status With Event Handlers for an example.

In order to use this functionality, you should deploy the applet with java_status_events parameter set to true .

The article Applet Status and Event Handlers outlines the status and events:

Status

• LOADING = 1 - Applet is loading
• READY = 2 - Applet has loaded completely and is ready to receive JavaScript calls
• ERROR = 3 - Error while loading applet

Events

• onLoad : Occurs when applet status is READY . Applet has finished loading and is ready to receive JavaScript calls.
• onStop : Occurs when applet has stopped.
• onError : Occurs when applet status is ERROR . An error has occurred while loading the applet.

You can register or determine an event handler in the JavaScript code of a web page as shown in the following code snippets.

 // use an anonymous function applet.onLoad(function() { //event handler for ready state } // use a regular function function onLoadHandler() { // event handler for ready state } // Use method form applet.onLoad(onLoadHandler); // Use attribute form applet.onLoad = onLoadHandler;