Is your web application platform based on ASP.net technology? Would you
like to leverage the Java platform's ubiquity to provide a rich user experience when users
visit your web site? You can develop secure rich Internet applications (RIAs - applets
and Java Web Start applications) by using the Java or the JavaFX language.
Java client technology integrates seamlessly with ASP.net technology.
In this article, we will explore various mechanisms by which Java applets
can interact with ASP.net web pages.
Here is a short screencast (about two and half minutes) that shows how an applet
can interact with an ASP.net page. View this screencast to better
understand the context for the rest of this article.
Deploying an Applet in an ASP.net Page
Use the Deployment Toolkit script to deploy an applet in an ASP.net page as
shown in the following code snippet:
An applet (running on the client) can interact with an ASP.net page
(running on the server) by using the following mechanisms:
Cookies – An applet can set and retrieve cookies set by ASP.net pages.
Updating HTML elements and ASP.net controls – An applet can update
the values of HTML elements and ASP.net controls in the parent web page by
using the LiveConnect feature.
Directly invoking an ASP.net page – An applet can use the
java.net.URLConnection class to invoke an ASP.net page, pass
parameters to the page, and retrieve a response.
Modes of Interaction
Cookies
Cookies can be used to share data between an applet and an ASP.net page.
An applet can retrieve cookies set by an ASP.net page. By the same token,
an ASP.net page can also retrieve cookies set by an applet.
In the code snippet shown next, the MapApplet class uses the
java.net.CookieHandler
class to retrieve the userName cookie set by the applet's parent
web page. The text "Hello <user name>" is displayed on the top left
corner of the applet.
private void getUserNameFromCookie() {
try {
// get the cookies that are applicable for this applet's parent web page
URL docBaseUrl = this.getDocumentBase();
CookieHandler cookieHandler = CookieHandler.getDefault();
java.util.Map<String, List<String>> headers =
cookieHandler.get(docBaseUrl.toURI(),
new HashMap<String,List<String>>());
if (headers.isEmpty()) {
System.out.println("No cookies found!");
} else {
getUserNameFromHeader(headers);
}
} catch(Exception e) {
...
}
}
private void getUserNameFromHeader(java.util.Map<String, List<String>> headers) {
for (String key : headers.keySet()) {
for (String value : headers.get(key)) {
if (key.equals("Cookie") && value.startsWith("userName")) {
userName = value.split("=")[1];
}
}
}
}
Note: You will need to sign your applet when using the
java.net.CookieHandler API. If you do not wish to sign your applet,
you can retrieve the value of a cookie by using JavaScript code in the ASP .net page.
This value can be accessed by the applet in one of the following ways:
The applet can use the LiveConnect feature to interact with JavaScript code and
access the value of the cookie. See
Invoking
JavaScript Code From an Applet for more information.
Updating ASP.net Page With LiveConnect
An applet can interact with the JavaScript code in its parent web page by
using the LiveConnect feature. The applet can invoke JavaScript functions
and access JavaScript variables to update the contents of its parent web page.
JavaScript code in the web page can also invoke applet methods.
In the following code snippet, the MapApplet class uses an
instance of the netscape.javascript.JSObject class to update
the contents of the asp:TextBox ID="addresses" control.
MapApplet.java
public void updateWebPage(String street, String city, String state) {
char result = invokeAspPage(street, city, state);
if (result == '1') {
window.call("writeAddressOnPage", new Object[] {street, city, state});
}
}
Default.aspx
<body>
...
<script type="text/javascript" language="javascript">
function writeAddressOnPage(street, city, state) {
var address = street + ", " + city + ", " + state;
var form = document.getElementById("addrForm");
var prevValue = form.elements["addresses"].value;
form.elements["addresses"].value = prevValue + "\n" + address;
}
</script>
<form id="addrForm" runat="server">
<div>
<p>Addresses saved to your address book:</p>
<asp:TextBox ID="addresses" TextMode="MultiLine" Rows="6"
Columns="60" runat="server" ></asp:TextBox>
</div>
</form>
...
</body>
When a form is posted, form field values become available to the next ASP.net
page through the Request object. You might also choose to update
hidden form fields with the applet's data.
Invoking an ASP.net Page
An applet can invoke an ASP.net page by using the
java.net.URLConnection class. In the following code snippet,
the MapApplet class opens a connection to the
FileWriter.aspx page, passes parameters by using the connection's
output stream, and receives a result by reading the connection's input
stream.
MapApplet.java
public char invokeAspPage(String street, String city, String state) {
char [] result = {'0'};
...
String urlString = baseUrl + "FileWriter.aspx";
URL url = new URL(urlString);
URLConnection connection = url.openConnection();
connection.setDoOutput(true);
// send parameter to url connection
OutputStreamWriter out = new OutputStreamWriter(
connection.getOutputStream());
out.write("addresses=" + URLEncoder.encode(address, "UTF-8"));
out.close();
// read response from url connection
BufferedReader in = new BufferedReader(
new InputStreamReader(
connection.getInputStream()));
in.read(result);
in.close();
...
return result[0];
}
The FileWriter.aspx page writes the given address information to
the userData/addresses.txt text file on the ASP.net server.
The page returns a character value of '1' if the address is written successfully.
As shown in this article, there are a number of ways by which an applet can
interact with an ASP.net page. Choose the option that works best for your
application. We would love to hear feedback about this article! If you are
using other creative ways to get applets to play well with ASP.net pages,
share your insights with the community!
Source Code
Download the ASP.net project and the Java code (Netbeans project) to
experiment further! Click on the following links to view individual source files:
We welcome your participation in our community. Please keep your comments civil and on
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