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442

Chapter 17 Using Applets As Servlet Front Ends

4. Set any desired HTTP headers. If you want to set HTTP 

request headers (see Chapter 4), you can use 

setRequest 

Property

 to do so. 

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

5. Create an 

ObjectInputStream

. The constructor for this class 

simply takes the raw input stream from the 

URLConnection

. It 

is at the point where you create the input stream that the con 

nection to the Web server is actually established.

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();

The Server Side

A servlet needs to perform the following four steps to send serialized data

structures to an applet. Assume that 

request

 and 

response

 are the 

Http 

ServletRequest

 and 

HttpServletResponse

 objects supplied to the 

doGet

and 

doPost

 methods. Again, these steps are simplified slightly by the omis 

sion of the required 

try

/

catch

 blocks.

1. Specify that binary content is being sent. This task is 

accomplished by designating 

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 read 

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

discussion of 

Content Type

 in Section 7.2 (HTTP 1.1 

Response Headers and Their Meaning) for more information 

on MIME types.

String contentType =

"application/x java serialized object";

response.setContentType(contentType);

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