Websaver

Brad Fitzpatrick, <bradfitz@bradfitz.com>

What is Websaver?

Websaver is a set of Java classes that communicates with a Perl server on the webserver that allow the loading, saving, and listing of files on the server, in a protected file space. Using Websaver, it is possible to make applets that load and save their state. For instace, in a drawing program, users could save their pictures and other people could potentially load them, depending on the permissions they were saved with.

Installing the server

The first step to using Websaver is installing the server component. A shell script has been written to make this very easy. Log into cubist.cs.washington.edu and type what's shown in bold below:

[username@cubist]$ ~tanimoto/websaver/install_websaver.sh

You should now have your very-own Websaver CGI script installed at:

http://cubist.cs.washington.edu/~username/Websaver.cgi

Usage - in your applet

Download the Java Sources

Download this ZIP file of all the .java files you'll need for this, and unzip them into your applet's directory. If you're using J++, you may also need to add them to the current project.

Setup your Applet Parameters

Instead of hard-coding the path to the server in your applet, it's best to pass it as a parameter to the applet from your HTML file. Add in a parameter like this:

<APPLET CODE="MyApplet.class" WIDTH=600 HEIGHT=400>
<PARAM NAME="websaver" 
       VALUE="http://cubist.cs.washington.edu/~username/Websaver.cgi">
</APPLET>

Changes to your applet class

Implement WebsaverDialogListener
If you want your applet to receive notifications when somebody requests to load or save a file from the supplied dialog boxes, you'll have to add WebsaverDialogListener to the list of interfaces your applet supports. Then, you'll also need to add these two functions to your applet to get it to compile:

Add private WebsaverConnection & Dialog Boxes
Add the following member variables to your class, for the Websaver connection and load/save dialog boxes, respectively:

    private WebsaverConnection wsConn;
    private WebsaverDialogLoad dlgLoad;
    private WebsaverDialogSave dlgSave;
    private String lastFilename; // last file loaded or saved

Add private buttons for loading and saving.
Just like any other buttons, you'll need to make two buttons, one for bringing up the load dialog, and one for the save dialog. You'll also have to add this as an actionListener for those buttons, just like other buttons you add. More on this later.

Create your WebsaverConnection & Dialogs

In your applet's init() function, initialize your WebsaverConnection and dialog boxes like so:

	// make all the websaver stuff
	String websaver = getParameter("websaver");
	if (websaver != null) {
	    // make the save button
	    btnSave = new Button("Save");
	    btnSave.addActionListener(this);
	    buttonPanel.add(btnSave);
	    
	    // make the load button
	    btnLoad = new Button("Load");
	    btnLoad.addActionListener(this);
	    buttonPanel.add(btnLoad);
	    
	    wsConn = new WebsaverConnection(websaver, "J2_applet");
	    dlgLoad = new WebsaverDialogLoad(wsConn, true);
	    dlgSave = new WebsaverDialogSave(wsConn, true);
	    dlgLoad.addWebsaverDialogListener(this);
	    dlgSave.addWebsaverDialogListener(this);
	}

Make your load & save boxes show the dialogs

In your actionPerformed(), add the bold code:

    public void actionPerformed(ActionEvent evt)
    {
        Object source = evt.getSource();
        if ((Button)source == btnSave) {
	    dlgSave.setFilename(lastFilename);
	    dlgSave.showDialog(this);
	}
	else if ((Button)source == btnLoad) {
	    dlgLoad.showDialog(this);
	}
    }

Do the loading and saving!

Now it's time to do the actual loading and saving... remember those methods websaverFileLoad and websaverFileSave you made earlier? It's time to fill those in. The parts in bold below you have to do. The rest you can (and should) copy verbatim. Note that you can do anything you want with the Input and Output streams, but object serialization is the fastest and easiest way to save things.

    public void websaverFileSave (WebsaverDialogEvent evt)
    {
	String filename = evt.getFilename();
	lastFilename = filename;
	try {
	    WebsaverOutputStream wos = new WebsaverOutputStream(wsConn, 
	                                                        filename,
								evt.getPassword(), 
								true);
	    ObjectOutputStream oos = new ObjectOutputStream(wos);

	    // YOUR JOB:  Save all your objects, like this:
	    // oos.writeObject(bgColor);
	    // oos.writeObject(fgColor);
	    // oos.writeObject(activeObjects);

	    oos.close();
	    dlgSave.hideDialog();
	} catch (Exception e) {
	    System.out.println(e.toString());
	    DialogMessageBox dia = new DialogMessageBox(dlgLoad, "Error", e.toString());
	}
    }

    public void websaverFileLoad (WebsaverDialogEvent evt)
    {
	String filename = evt.getFilename();
	lastFilename = filename;
	try {
	    WebsaverInputStream wis = new WebsaverInputStream(wsConn, 
	                                                      filename,
							      evt.getPassword());
	    ObjectInputStream ois = new ObjectInputStream(wis);

	    // YOUR JOB:  Load in all your objects, like this:
	    // bgColor = (Color) ois.readObject();
	    // fgColor = (Color) ois.readObject();
	    // activeObjects = (Vector) ois.readObject();

	    ois.close();
	    dlgLoad.hideDialog();
	} catch (Exception e) {
	    System.out.println(e.toString());
	    DialogMessageBox dia = new DialogMessageBox(dlgLoad, "Error", e.toString());
	}
    }

That's it!

That's it... you're done. Some things to note:

Applets can only open socket connections to the host they were downloaded from, so if you're testing this from home, unless you relax your applet viewer's security settings, you will not be able to load/save from cubist. You have to upload all your .class files and your .html, and load your applet over the web. The appletviewer shipped with JDK 1.1.8 lets you turn off this restriction, but I don't know if J++ lets you or not.
All the Websaver*.java classes are pretty well-documented. If not, bug me and I'll comment them better.

Need Help?

Post a message to the class mailing list at cse341@cs.washington.edu and if somebody doesn't help you by the time I check my mail, I'll help you out.