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A.6 Generating the Server Response: HTTP Status Codes

527

A.6 Generating the Server Response: 

HTTP Status Codes

Format of an HTTP Response

Status line (HTTP version, status code, message), response headers, blank

line, document, in that order. For example:

HTTP/1.1 200 OK

Content Type: text/plain

Hello World

Methods That Set Status Codes

These are methods in 

HttpServletResponse

. Set status codes before you

send any document content to browser.

  public void setStatus(int statusCode) 

Use a constant for the code, not an explicit 

int

.

  public void sendError(int code, String message) 

Wraps message inside small HTML document.

  public void sendRedirect(String url) 

Relative URLs permitted in 2.2.

Status Code Categories

  100 199: informational; client should respond with some other action. 

  200 299: request was successful. 

  300 399: file has moved. Usually includes a Location header indicating 

new address. 

  400 499: error by client. 

  500 599: error by server. 

Common HTTP 1.1 Status Codes

  200 (OK): Everything is fine; document follows. Default for servlets.

  204 (No Content): Browser should keep displaying previous 

document.

  301 (Moved Permanently): Requested document permanently 

moved elsewhere (indicated in 

Location

 header). Browsers go to new 

location automatically.

  302 (Found): Requested document temporarily moved elsewhere 

(indicated in Location header). Browsers go to new location 

automatically. Servlets should use 

sendRedirect

, not 

setStatus

, 

when setting this header. See example in Section 6.3.

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

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