Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

A.17 Using Applets As Servlet Front Ends

549

Sending Serialized Data: The Applet Code

1. Create a 

URL

 object referring to the applet's home host. It is 

best to specify a URL suffix and construct the rest of the URL 

automatically.

URL currentPage = getCodeBase();

String protocol = currentPage.getProtocol();

String host = currentPage.getHost();

int port = currentPage.getPort();

String urlSuffix = "/servlet/SomeServlet";

URL dataURL = new URL(protocol, host, port, urlSuffix);

2. Create a 

URLConnection

 object. The 

openConnection

method of 

URL

 returns a 

URLConnection

 object. This object 

will be used to obtain streams with which to communicate. 

URLConnection connection = dataURL.openConnection();

3. Instruct the browser not to cache the URL data. 

connection.setUseCaches(false); 

4. Set any desired HTTP headers. 

connection.setRequestProperty("header", "value");

5. Create an 

ObjectInputStream

. The constructor for this class 

simply takes the raw input stream from the 

URLConnection

. 

ObjectInputStream in =

new ObjectInputStream(connection.getInputStream());

6. Read the data structure with 

readObject

. The return type 

of 

readObject

 is 

Object

, so you need to make a typecast to 

whatever more specific type the server actually sent.

SomeClass value = (SomeClass)in.readObject();

doSomethingWith(value);

7. Close the input stream. 

in.close();

Sending Serialized Data: The Servlet Code

1. Specify that binary content is being sent. To do so, designate

application/x java serialized object

as the MIME type of the response. This is the standard MIME 

type for objects encoded with an 

ObjectOutputStream

, 

although in practice, since the applet (not the browser) is reading 

the result, the MIME type is not very important. See the discus 

sion of 

Content Type

 in Section 7.2 for more information on 

MIME types.

String contentType =

"application/x java serialized object";

response.setContentType(contentType);

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.