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528

Appendix A

Servlet and JSP Quick Reference

  401 (Unauthorized): Browser tried to access password protected page 

without proper 

Authorization

 header. See example in Section 4.5.

  404 (Not Found): No such page. Servlets should use 

sendError

 to set 

this header. See example in Section 6.3.

A.7 Generating the Server Response: HTTP 

Response Headers

Setting Arbitrary Headers

These are methods in 

HttpServletResponse

. Set response headers before

you send any document content to browser.

  public void setHeader(String headerName, String headerValue) 

Sets an arbitrary header.

  public void setDateHeader(String headerName,

long milliseconds)

Converts milliseconds since 1970 to a date string in GMT format.

  public void setIntHeader(String headerName, int headerValue) 

Prevents need to convert 

int

 to 

String

 before calling 

setHeader

.

  addHeader, addDateHeader, addIntHeader 

Adds new occurrence of header instead of replacing. 2.2 only.

Setting Common Headers

  setContentType: Sets the 

Content Type

 header. Servlets almost 

always use this. See Table 7.1 for the most common MIME types.

  setContentLength: Sets the 

Content Length

 header. Used for 

persistent HTTP connections. Use 

ByteArrayOutputStream

 to buffer 

document before sending it, to determine size. See Section 7.4 for an 

example.

  addCookie: Adds a value to the 

Set Cookie

 header. See Chapter 8.

  sendRedirect: Sets the 

Location

 header (plus changes status code). 

See example in Section 6.3.

Common HTTP 1.1 Response Headers

  Allow: the request methods server supports. Automatically set by the 

default 

service

 method when servlet receives 

OPTIONS

 requests.

  Cache Control: A 

no cache

 value prevents browsers from caching 

results. Send 

Pragma

 header with same value in case browser only 

understands HTTP 1.0.

  Content Encoding: the way document is encoded. Browser reverses 

this encoding before handling document. Servlets must confirm that 

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