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CS3220 Web and Internet Programming Generating HTTP Responses
Chengyu Sun California State University, Los Angeles
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HTTP Response As Output
Browser Application Server HTTP request HTTP response input output program
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HTTP Response Example HTTP/1.1 200 OK
Content-Type: text/html;charset=ISO Content-Length: 168 Date: Sun, 03 Oct :26:57 GMT Server: Apache-Coyote/1.1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html><head><title>Servlet Life Cycle</title></head> <body> n is 299 and m is 440 </body> </html>
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HTTP Response Status line Protocol Status code Header [Message body]
![HTTP Response Status line Protocol Status code Header [Message body]](http://slideplayer.com./slide/13445072/80/images/4/HTTP+Response+Status+line+Protocol+Status+code+Header+%5BMessage+body%5D.jpg "HTTP Response Status line Protocol Status code Header [Message body]")
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Common Status Codes 200 (OK) 401 (Unauthorized) 403 (Forbidden)
404 (Not Found) 500 (Internal Server Error)
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Status Codes 100 – 199: Informational. Client should respond with further action 200 – 299: Request is successful 300 – 399: Files have moved 400 – 499: Error by the client 500 – 599: Error by the server
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Redirect Codes 301 (Moved Permanently) 302 (Found) 303 (See Other)
GET 302 (Found) a.k.a. (Moved Temporarily) 303 (See Other) GET and POST 307 (Temporary Redirect) GET but not POST
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<error-page> in web.xml
Showing customized error pages for common errors, e.g. 404 Page Not Found Example: <error-page> <error-code>404</error-code> <location>/WEB-INF/404.html</location> </error-page> <error-code>403</error-code> <location>/WEB-INF/403.html</location>
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Header Fields Request Response Accept Accept-Charset Accept-Encoding
Accept-Language Connection Content-Length Cookies Response Content-Type Content-Encoding Content-Language Connection Content-Length Set-Cookie
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More Response Header Fields
Location for redirect Refresh “Push” Incremental display Content-Disposition (RFC2183) RFC2616, Section 14
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HttpServletResponse
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Header Methods in HttpServletResponse
addHeader(), setHeader() addIntHeader(), setIntHeader() addDateHeader(), setDateHeader() containsHeader()
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More HttpServletResponse Methods
setContentType( String type ) sendRedirect( String location ) Set status code to 302 getWriter() For text responses, e.g. HTML pages getOutputStream() For binary responses, e.g. images
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Example: Add Revisited
Redirect the user back to the input form if the parameters are missing or invalid sendRedirect() does not terminate the execution of doGet() or doPost()
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Example: Countdown Automatically refreshes the display every second
The Refresh header
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File Upload and Download in Web Applications
Pictures on online albums and social networking sites Attachments in web forum posts and web s Resumes on job search sites Student homework submissions in learning management systems … …
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File Upload – The Form <form action="FileUploadHandler"
method="post" enctype="multipart/form-data"> First file: <input type="file" name="file1" /> <br /> Second file: <input type="file" name="file2" /> <br /> <input type="submit" name="upload" value="Upload" /> </form>
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File Upload – The Request
POST / HTTP/1.1 Host: cs.calstatela.edu:4040 […] Cookie: SITESERVER=ID=289f7e a2d7d1e6e44f931195 Content-Type: multipart/form-data; boundary= Content-Length: 509 Content-Disposition: form-data; name="file1"; filename="test.txt" Content-Type: text/plain this is a test file. Content-Disposition: form-data; name="file2"; filename="test2.txt.gz" Content-Type: application/x-gzip ?????????UC
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Apache commons-fileupload
Parse an HTTP request and retrieve the uploaded files Requires Apache commons-io
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Paths $PROJECT/WEB-INF/lib for additional jar files in a webapp
$WORKSPACE/.metadata/.plugins/org.eclipse.wst.server.core is where webapp is deployed locally getServletContext().getRealPath(“/path_within_webapp") to get the absolute file system path to the file or folder
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Important Classes FileItem in commons-fileupload - File in java.io -
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Example: Download Download an image file from the server File I/O
Content type Binary response Content-Length and Content-Disposition header
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Summary HTTP response format
Status code ranges and some common status codes Generate non-HTML responses Use of headers Writer vs. OutputStream
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