Advance java session 11
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The document discusses implicit objects in JSP pages that provide access to servlet capabilities without needing to be declared. These implicit objects include request, response, session, application, out, exception, page, and pageContext. The document describes each object's scope and associated class, and provides examples of how to use the exception, session, request, response, application, config, out, and pageContext objects in JSP pages.
Advance java session 11
- 2. Agenda • Understanding built In Objects • Request, response • Out • session • exception • page and application scope
- 3. Implicit Object • A JSP page has access to certain implicit objects that are always available, without being declared first • Created by container • Corresponds to classes defined in Servlet
- 4. Implicit Object - Provide access to many servlet capabilities within a JSP - Four scopes • Application scope - Objects owned by the container application - Any servlet or JSP can manipulate these objects • Session scope - Objects exist for duration of client’s browsing session - Objects go out of scope when client terminates session or when session timeout occurs • Request scope - Objects exist for duration of client request - Objects go out of scope after response sent to client • Page scope - Objects that exist only in page in which they are defined - Each page has its own instance of these objects
- 5. Implicit Object Implicit object Description Application Scope application This javax.servlet.ServletContext object represents the container in which the JSP executes. Page Scope config This javax.servlet.ServletConfig object represents the JSP configuration options. As with servlets, configuration options can be specified in a Web application descriptor. exception This java.lang.Throwable object represents the exception that is passed to the JSP error page. This object is available only in a JSP error page. out This javax.servlet.jsp.JspWriter object writes text as part of the response to a request. This object is used implicitly with JSP expressions and actions that insert string content in a response. page This java.lang.Object object represents the this reference for the current JSP instance. pageContext This javax.servlet.jsp.PageContext object hides the implementation details of the underlying servlet and JSP container and provides JSP programmers with access to the implicit objects discussed in this table. response This object represents the response to the client and is normally an instance of a class that implements HttpServletResponse (package javax.servlet.http). If a protocol other than HTTP is used, this object is an instance of a class that implements javax.servlet.ServletResponse. Request Scope request This object represents the client request. The object normally is an instance of a class that implements HttpServletRequest (package javax.servlet.http). If a protocol other than HTTP is used, this object is an instance of a subclass of javax.servlet.Servlet- Request. Session Scope session This javax.servlet.http.HttpSession object represents the client session information if such a session has been created. This object is available only in pages that participate in a session.
- 6. Implicit Object and their classes • request (HttpServletRequest) • response (HttpServletRepsonse) • session (HttpSession) • application(ServletContext) • out (of type JspWriter) • config (ServletConfig) • pageContext(this)
- 7. Creating an exception with an error page • Determine the exception thrown • In each of your JSP, include the name of the error page - <%@ page errorPage="errorpage.jsp" %> • Develop an error page, it should include - <%@ page isErrorPage="true" %> • In the error page, use the exception reference to display exception information <%= exception.toString() %>
- 8. About Exception Object • Instance of java.lang.Throwable • It is available in those pages where isError page directive is set to true • Important methods - public String getlocalizedMessage() - public String getMessage() - public void printStackTrace() - public void printStackTrace(PrintStream ps) - public void printStackTrace(PrintWriter pw)
- 9. Session Object • This denotes the data associated with a specific session of user. • The class or the interface name of the object Session is http.HttpSession. • The previous two objects, request and response, are used to pass information from web browser to server and from server to web browser respectively. • The Session Object provides the connection or association between the client and the server. • The main use of Session Objects is for maintaining states hen there are multiple page requests.
- 10. Session Object • It is an instanceof javax.servlet.http.HttpSession • getAttributes returns the bounded object or null • getAttributes return Enumeration of String Objects containing names of all Object bounded to the session • getCreationTime returns the time in millseconds when the session • isNew() returns true if the server has created a session that hasn’t been accessed by the client • getId() returns String Object containing a unique identifier for his session • Invalidate() invalidates the session and unbinds any object bound to it
- 11. Request Object • The request object is an instance of a javax.servlet.http.HttpServletRequest object. Each time a client requests a page the JSP engine creates a new object to represent that request. • The request object provides methods to get HTTP header information including form data, cookies, HTTP methods etc.
- 12. Request Object methods • public Object getAttribute(String name) • getAttributeNames() returns an Enumeration containing the attribute names available to the invoking ServletRequest object: • public java.util.Enumeration getAttributeNames() • getAuthType() returns the name of the authentication scheme used in the request or null if no authentication scheme was used. It returns one of the constants BASIC_AUTH, FORM_AUTH, CLIENT_CERT_AUTH, or DIGEST_AUTH, or it returns null if the request wasn't authenticated: • public String getAuthType() • getCharacterEncoding() returns a String object containing the character encoding used in the body of the request or null if there's no encoding: • public String getCharacterEncoding()
- 13. Request Object methods • public Object getAttribute(String name) • getAttributeNames() returns an Enumeration containing the attribute names available to the invoking ServletRequest object: • public java.util.Enumeration getAttributeNames() • getAuthType() returns the name of the authentication scheme used in the request or null if no authentication scheme was used. It returns one of the constants BASIC_AUTH, FORM_AUTH, CLIENT_CERT_AUTH, or DIGEST_AUTH, or it returns null if the request wasn't authenticated: • public String getAuthType() • getCharacterEncoding() returns a String object containing the character encoding used in the body of the request or null if there's no encoding: • public String getCharacterEncoding()
- 14. Response Object • The response object is an instance of a javax.servlet.http.HttpServletResponse object. Just as the server creates the request object, it also creates an object to represent the response to the client. • The response object also defines the interfaces that deal with creating new HTTP headers. Through this object the JSP programmer can add new cookies or date stamps, HTTP status codes etc.
- 15. out Object • The out implicit object is an instance of a javax.servlet.jsp.JspWriter object and is used to send content in a response. • The initial JspWriter object is instantiated differently depending on whether the page is buffered or not. Buffering can be easily turned off by using the buffered='false' attribute of the page directive. • The JspWriter object contains most of the same methods as the java.io.PrintWriter class. However, JspWriter has some additional methods designed to deal with buffering. Unlike the PrintWriter object, JspWriter throws IOExceptions.
- 16. application Object • The application object is direct wrapper around the ServletContext object for the generated Servlet and in reality an instance of a javax.servlet.ServletContext object. • This object is a representation of the JSP page through its entire lifecycle. This object is created when the JSP page is initialized and will be removed when the JSP page is removed by the jspDestroy() method. • By adding an attribute to application, you can ensure that all JSP files that make up your web application have access to it.
- 17. config Object • The config object is an instantiation of javax.servlet.ServletConfig and is a direct wrapper around the ServletConfig object for the generated servlet. • This object allows the JSP programmer access to the Servlet or JSP engine initialization parameters such as the paths or file locations etc.
- 18. pageContext Object • The pageContext object is an instance of a javax.servlet.jsp.PageContext object. The pageContext object is used to represent the entire JSP page. • This object is intended as a means to access information about the page while avoiding most of the implementation details. • This object stores references to the request and response objects for each request. The application, config, session, and out objects are derived by accessing attributes of this object. • The pageContext object also contains information about the directives issued to the JSP page, including the buffering information, the errorPageURL, and page scope. • The PageContext class defines several fields, including PAGE_SCOPE, REQUEST_SCOPE, SESSION_SCOPE, and APPLICATION_SCOPE, which identify the four scopes. It also supports more than 40 methods, about half of which are inherited from the javax.servlet.jsp. JspContext class
- 19. Summary • Implicit Objects - page - request - session - application - response - out - cexception