Java Servlets

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Servlets CS-328 Dick Steflik

What is a servlet • A Java application run on a thread of the webserver in response to an HTTP GET or POST request. • The servlet is used to generate Dynamic content to return to the requesting browser – may be HTML – may be XML – may be POT

The Servlet Model

HTTP Get or Post BROWSER

Java Enabled Webserver

HTML

J V

Servlet

M

Data Base

Invoking a servlet • <servlet> tag – webserver must be enabled for server side embeds

• “action” attribute of
tag – can be GET or POST (HTTP 1.0) – can also be “PUT” (HTTP 1.1)

Servlets Provide • Protocol independent and platform independent server side components • A Common API (Servlet API) • Dynamic loading either locally or over the network • Security (servlet security model) • More safe than CGI scripts – runs as thread not as child process

Life cycle • Once invoked a servlet has a life cycle that is supported by a set of life cycle methods that are automatically run by the webserver – – – –

init() - run when initially loaded service() - for performing the servlets service destroy() - for destroying the servlet object doGet() - only for HTTP servlets and is used for processing HTTP GET requests – doPost() - only for HTTP servlets and is used for processing HTTP POST requests

Servlet Interface • All servlets must implement the Servlet interface • Methods: – – – – –

init() service() destroy() getServletConfig() getServletInfo()

ServletConfig Interface • Implemented by network services to pass configuration info to a servlet when it is first loaded • Methods: – getInitParameter(String name) - returns a String value of the requested parameter – getInitParameterNames() - returns an enumeration of the names of the initialization parameters – getServletContext() - returns a ServerContext object that contains the servlet’s context

ServletContext Interface • Implemented by network services, gives servlets access to environmental information and allows logging of events. • Methods: – getServlet() - returns an initialized and ready to run Servlet object. – getServlets() - returns an enumeration of all of the Servlet objects in this server that are in the same name space (always includes the servlet itself) – getServerInfo() - returns info about the network service the Servlet is running under – getAttribute(String name) - returns the value of the named attribute – getRealPath(String name) - returns the actual path of the named virtual path – getMimeType(String file) - returns mime type of the named file –

ServletRequest Interface • •

Provides means to get information from the HTTP request header Methods: – – – – – – – – – – –

getProtocol() getScheme() getParameterNames() getParameter() getParameterValues() getAttribute() getContentLength() getContentType() getInputStream() getRemoteAddr() getRemoteHost()

(more) • getServerName() • getServerPort() • getRealPath()

ServletResponse Interface • Provides means to build HTTP response header • Methods: – setContentLength(int len) – setContentType(String type) – getOutputStream() - returns a ServletOutputStream for writing the response data

GenericServlet Class • Abstract class that implements Servlet and ServletConfig

HttpServlet Class • Abstract class that extends GenericServlet Class to provide a framework for the HTTP Protocol • doGet(HttpServletRequest req, HttpServletResponse resp) • doPost (HttpServletRequest req, HttpServletResponse resp) • getLastModified((HttpServletRequest req)

HttpServletRequest Interface • • • • • • • •

getAuthType() getHeaderNames() getHeader() getDateHeader() getIntHeader() getMethod() getQueryString() getRemoteUser()

• • • •

getRequestURI() getServletPath() getPathInfo() getPathTranslated()

HttpServletResponse Interface • containsHeader(String name) • setHeader(String name,String value) • setDateHeader(String name, long value) • setIntHeader(String name, int value) • setStatus(int sc)

• setStatus(int sc, String msg) • sendError(int sc) • sendError(int sc, String msg) • sendRedirect(String location)

HttpUtils Class • getRequestURL(HttpServletRequest req) • parsePostData(int ServletStream) - returns a hash table containing the name/value pairs • parseQueryString(String s) - returns a hash table containing the name/value pairs

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