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Wednesday, 26 March 2014

Servlet - HTTP Servlet Request

In this tutorials we are going to see about HttpServletRequest .
HttpServletRequest Extends the ServletRequest interface to provide request information for HTTP servlets. This tutorial written based on Servlet 3.0.
The servlet container creates an HttpServletRequest object and passes it as an argument to the servlet's service methods (doGet, doPost, etc).
When user request the web page, browser send the lot of information to server which can’t be read directly because these information's send as a part of header of Http Request.
Methods available in HttpServletRequest
S.No
Method with Description
1 boolean authenticate(HttpServletResponse response) Use the container login mechanism configured for the ServletContext to authenticate the user making this request.This method may modify and commit the argument HttpServletResponse.
2 void login(String username,String password) Validate the provided username and password in the password validation realm used by the web container login mechanism configured for the ServletContext.
This method returns without throwing a ServletException when the login mechanism configured for the ServletContext supports username password validation, and when, at the time of the call to login, the identity of the caller of the request had not been established (i.e, all of getUserPrincipal, getRemoteUser, and getAuthType return null), and when validation of the provided credentials is successful. Otherwise, this method throws a ServletException as described below.
When this method returns without throwing an exception, it must have established non-null values as the values returned by getUserPrincipal, getRemoteUser, and getAuthType.
3 void logout() Establish null as the value returned when getUserPrincipal, getRemoteUser, and getAuthType is called on the request.
4 java.util.Collection<Part> getParts() Gets all the Part components of this request, provided that it is of type multipart/form-data. If this request is of type multipart/form-data, but does not contain any Part components, the returned Collection will be empty.
Any changes to the returned Collection must not affect this HttpServletRequest.
5 Part getPart(java.lang.String name)
Gets the Part with the given name.
6 String getAuthType()
Returns the name of the authentication scheme used to protect the servlet. All servlet containers support basic, form and client certificate authentication, and may additionally support digest authentication. If the servlet is not authenticated null is returned.
Same as the value of the CGI variable AUTH_TYPE.
7 Cookie[] getCookies() Returns an array containing all of the Cookie objects the client sent with this request. This method returns null if no cookies were sent.
8 long getDateHeader(String name) Returns the value of the specified request header as a long value that represents a Date object. Use this method with headers that contain dates, such as If-Modified-Since.
The date is returned as the number of milliseconds since January 1, 1970 GMT. The header name is case insensitive.
If the request did not have a header of the specified name, this method returns -1. If the header can't be converted to a date, the method throws an IllegalArgumentException.
9 String getHeader(String name)
Returns the value of the specified request header as a String. If the request did not include a header of the specified name, this method returns null. If there are multiple headers with the same name, this method returns the first head in the request. The header name is case insensitive. You can use this method with any request header.
10 java.util.Enumeration<String> getHeaders(String name) Returns all the values of the specified request header as an Enumeration of String objects. Some headers, such as Accept-Language can be sent by clients as several headers each with a different value rather than sending the header as a comma separated list.
If the request did not include any headers of the specified name, this method returns an empty Enumeration. The header name is case insensitive. You can use this method with any request header.
11 java.util.Enumeration<String> getHeaderNames()
Returns an enumeration of all the header names this request contains. If the request has no headers, this method returns an empty enumeration.
Some servlet containers do not allow servlets to access headers using this method, in which case this method returns null
12 int getIntHeader(String name)
Returns the value of the specified request header as an int. If the request does not have a header of the specified name, this method returns -1. If the header cannot be converted to an integer, this method throws a NumberFormatException.
The header name is case insensitive.
13 String getMethod()
Returns the name of the HTTP method with which this request was made, for example, GET, POST, or PUT. Same as the value of the CGI variable REQUEST_METHOD.
14 String getPathInfo()
Returns any extra path information associated with the URL the client sent when it made this request. The extra path information follows the servlet path but
precedes the query string and will start with a "/" character.
This method returns null if there was no extra path information.
Same as the value of the CGI variable PATH_INFO.
15 String getPathTranslated() Returns any extra path information after the servlet name but before the query string, and translates it to a real path. Same as the value of the CGI variable PATH_TRANSLATED.
If the URL does not have any extra path information, this method returns null or the servlet container cannot translate the virtual path to a real path for any reason (such as when the web application is executed from an archive). The web container does not decode this string.
16 String getContextPath()
Returns the portion of the request URI that indicates the context of the request. The context path always comes first in a request URI. The path starts with a "/" character but does not end with a "/" character. For servlets in the default (root) context, this method returns "". The container does not decode this string.
It is possible that a servlet container may match a context by more than one context path. In such cases this method will return the actual context path used by the request and it may differ from the path returned by the ServletContext.getContextPath() method. The context path returned by ServletContext.getContextPath() should be considered as the prime or preferred context path of the application.
17 String getQueryString()
Returns the query string that is contained in the request URL after the path. This method returns null if the URL does not have a query string. Same as the value of the CGI variable QUERY_STRING.
18 String getRemoteUser() Returns the login of the user making this request, if the user has been authenticated, or null if the user has not been authenticated. Whether the user name is sent with each subsequent request depends on the browser and type of authentication. Same as the value of the CGI variable REMOTE_USER.
19 boolean isUserInRole(String role)
Returns a boolean indicating whether the authenticated user is included in the specified logical "role". Roles and role membership can be defined using deployment descriptors. If the user has not been authenticated, the method returns false.
20 java.security.Principal getUserPrincipal() Returns a java.security.Principal object containing the name of the current authenticated user. If the user has not been authenticated, the method returns null.
21 String getRequestedSessionId()
Returns the session ID specified by the client. This may not be the same as the ID of the current valid session for this request. If the client did not specify a session ID, this method returns null.
22 String getRequestURI()
Returns the part of this request's URL from the protocol name up to the query string in the first line of the HTTP request. The web container does not decode this String
23 StringBuffer getRequestURL()
Reconstructs the URL the client used to make the request. The returned URL contains a protocol, server name, port number, and server path, but it does not include query string parameters.
If this request has been forwarded using RequestDispatcher.forward(javax.servlet.ServletRequest, javax.servlet.ServletResponse), the server path in the reconstructed URL must reflect the path used to obtain the RequestDispatcher, and not the server path specified by the client.
Because this method returns a StringBuffer, not a string, you can modify the URL easily, for example, to append query parameters.
This method is useful for creating redirect messages and for reporting errors.
24 String getServletPath()
Returns the part of this request's URL that calls the servlet. This path starts with a "/" character and includes either the servlet name or a path to the servlet, but does not include any extra path information or a query string. Same as the value of the CGI variable SCRIPT_NAME.
This method will return an empty string ("") if the servlet used to process this request was matched using the "/*" pattern.
25 HttpSession getSession(boolean create)
Returns the current HttpSession associated with this request or, if there is no current session and create is true, returns a new session.
If create is false and the request has no valid HttpSession, this method returns null.
To make sure the session is properly maintained, you must call this method before the response is committed. If the container is using cookies to maintain session integrity and is asked to create a new session when the response is committed, an IllegalStateException is thrown.
26 HttpSession getSession()
Returns the current session associated with this request, or if the request does not have a session, creates one.
27 boolean isRequestedSessionIdValid() Checks whether the requested session ID is still valid.
If the client did not specify any session ID, this method returns false.
28 boolean isRequestedSessionIdFromCookie()
Checks whether the requested session ID came in as a cookie.
29 boolean isRequestedSessionIdFromURL()
Checks whether the requested session ID came in as part of the request URL.
30 boolean isRequestedSessionIdFromUrl()
Deprecated. As of Version 2.1 of the Java Servlet API, use isRequestedSessionIdFromURL() instead.
Fields Available in HttpServletRequest
Field
Description
static final String BASIC_AUTH String identifier for Basic authentication. Value "BASIC"
static final String FORM_AUTH String identifier for Form authentication. Value "FORM"
static final String CLIENT_CERT_AUTH String identifier for Client Certificate authentication. Value "CLIENT_CERT"
static final String DIGEST_AUTH String identifier for Digest authentication. Value "DIGEST"
Annamalai Thangaraj

Annamalai is working as Technical Lead in Leading Telecom company with 5+ years experience in Identity and Access Management , Telecom and Networks, BigData, Java, Spring, Struts, Hibernate, AngularJS, and Enterprise Web Application Development.

Website: Java Tutorials Corner

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Item Reviewed: Servlet - HTTP Servlet Request Rating: 5 Reviewed By: Annamalai Thangaraj