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Chapter 17 Using Applets As Servlet Front Ends

5. Create a 

ByteArrayOutputStream

 to buffer the data that 

will be sent to the server. The purpose of the 

ByteArray 

OutputStream

 here is the same as it is with the persistent 

(keep alive) HTTP connections shown in Section 7.4   to 

determine the size of the output so that the 

Content Length

header can be set. The 

ByteArrayOutputStream

 constructor 

specifies an initial buffer size, but this value is not critical 

since the buffer will grow automatically if necessary.

ByteArrayOutputStream byteStream =

new ByteArrayOutputStream(512);

6. Attach an output stream to the 

ByteArrayOutputStream

. 

Use a 

PrintWriter

 to send normal form data. To send serial 

ized data structures, use an 

ObjectOutputStream

 instead.

PrintWriter out = new PrintWriter(byteStream, true);

7. Put the data into the buffer. For form data, use 

print

. For 

high level serialized objects, use 

writeObject

.

String val1 = URLEncoder.encode(someVal1);

String val2 = URLEncoder.encode(someVal2);

String data = "param1=" + val1 +

"¶m2=" + val2; // Note '&'

out.print(data);

// Note print, not println

out.flush(); // Necessary since no println used

8. Set the 

Content Length

 header. This header is required for 

POST

 data, even though it is unused with 

GET

 requests.

connection.setRequestProperty

("Content Length", String.valueOf(byteStream.size()));

9. Set the 

Content Type

 header. Netscape uses 

multi 

part/form data

 by default, but regular form data requires a 

setting of 

application/x www form urlencoded

, which is 

the default with Internet Explorer. So, for portability you should 

set this value explicitly when sending regular form data. The 

value is irrelevant when sending serialized data.

connection.setRequestProperty

("Content Type", "application/x www form urlencoded");

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