JSP servlet summary

General Summary  

– Servlets are efficient, portable, powerful, and widely

accepted in industry

– Regardless of deployment server, run a free server on

your desktop for development

– Using Eclipse (or another IDE like NetBeans or IntelliJ

IDEA) greatly simplifies development and deployment

– Strongly consider JSF 2 as an alternative for new projects

Servlet Basic Summary

Main servlet code goes in doGet or doPost:

– The HttpServletRequest contains the incoming

information

– The HttpServletResponse lets you set outgoing

information

• Call setContentType to specify MIME type

• Call getWriter to obtain a Writer pointing to client (browser)

• Make sure output is legal HTML

• Give address with @WebServlet or web.xml

@WebServlet("/some-address")

public class SomeServlet extends HttpServlet { … }

• Resulting URL

– http://hostName/appName/some-address

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Form Data Summary

• Make a form: <form …> … </form>

– Relative URL for “action”. Textfields need “name”.

Should always have submit button.

• Read data: request.getParameter("name")

– Results in value as entered into form, not necessarily as

sent over network. I.e., not URL-encoded.

• Check for missing or malformed data

– Missing: null or empty string

– Special case: query data that contains special HTML

characters

• Need to be filtered if query data will be placed into

resultant HTML page

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Request Header Summary

HTTP is important

– Many servlet tasks can only be accomplished by making use of

HTTP headers coming from the browser

• Use request.getHeader for arbitrary header

– Remember to check for null

• Shortcuts discussed later

– Cookies, authorization info, content length, and content type

have shortcut methods

• Most important headers you read directly

– Accept

– Accept-Encoding

– Connection

– Referer

– User-Agent 26

Status Code Summary

HTTP is important

– Many servlet tasks can only be accomplished with HTTP

status codes

• Setting status codes

– Redirect user with response.sendRedirect(someURL)

• If you insert user-supplied data into the URL, encode with

URLEncoder.encode

– Send 404 error pages with sendError

– In general, set via response.setStatus

• Most important status codes

– 200 (default)

– 302 (forwarding; set with sendRedirect)

– 401 (password needed)

– 404 (not found; set with sendError)

Response Header Summary

HTTP is important

– Many servlet tasks can only be accomplished through use of HTTP

response headers

• Setting response headers

– In general, set with response.setHeader

– In special cases, set with response.setContentType,

response.setContentLength, response.addCookie, and

response.sendRedirect

• Most important response headers you set directly

– Cache-Control and Pragma

– Content-Disposition

– Content-Encoding

– Content-Length

– Expires

– Refresh

– WWW-Authenticate

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Cookie Summary

Basic functionality

– Cookies involve name/value pairs sent from server to

browser and automatically returned when the same page

(or possibly same site or domain) is visited later

• Cookies let you

– Track sessions (use higher-level session-tracking API)

– Permit users to avoid logging in at low-security sites

– Customize sites for different users

– Focus content or advertising

• Setting cookies

– Call Cookie constructor, set age, call response.addCookie

• Reading cookies

– Call request.getCookies, check for null, look through

array for matching name, use associated value

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Session Tracking Summary

Summary

• Sessions do not travel across network

– Only unique identifier does

• Get the session

– request.getSession

• Extract data from session

– session.getAttribute

• Do typecast and check for null

• If you cast to a generic type, use @SuppressWarnings

• Put data in session

– session.setAttribute

• Custom classes in sessions

– Should implement Serializable

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JSP Summary

JSP is more convenient, not more powerful

– JSP makes it easier to create and maintain HTML, while

still providing full access to servlet code

• JSP pages get translated into servlets

– It is the servlets that run at request time

– Client does not see anything JSP-related

• You still need to understand servlets

– Understanding how JSP really works

– Servlet code called from JSP

– Knowing when servlets are better than JSP

– Mixing servlets and JSP

• Other technologies use similar approach,

– But aren’t as portable and don’t let you use Java for the

“real code”

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pdfs from coreservelts.com