Jsp Objects / Implicit Objects in Jsp

Jsp Implicit Objects:

Implicit objects in JSP are Java objects that JSP Container makes available to developers in each page. These implicit Objects are automatically available in JSP. JSP Container provides developer to access these implicit objects in their program using JavaBeans and Servlets. These objects need not be declared or instantiated by the JSP author.

They are available only within the _jspService method and not in any declaration. These objects are called implicit objects since they are automatically instantiated by the container and are accessed using standard variables. The implicit objects are parsed by the container and inserted into the generated servlet code. They are available only within the jspService method and not in any declaration.

Many implicit objects available in JSP. Some of them are mentioned below:

request object in jsp

The request object has a request scope. It is an instance of the classes that implement javax.servlet.ServletRequest interface. It encapsulates the request coming from a client and uses the getParameter() method to access request parameters. It is passed to the JSP by the container as a parameter to the _jspService() method. This denotes the data included with the HTTP Request. The client first makes a request that is then passed to the server. The requested object is used to take the value from client’s web browser and pass it to the server. This is performed using HTTP request like headers, cookies and arguments.

response object in jsp

The response object has a page scope. It is an instance of the classes that implement javax.servlet.ServletResponse class. It encapsulates the response generated by the JSP to be sent to the client in response to the request. It is generated by the container and passed to the JSP as a parameter to the _jspService() method. This denotes the HTTP Response data. The result or the information from a request is denoted by this object. This is in contrast to the request object. The class or the interface name of the object response is http.HttpServletResponse. The object response is of type Javax.servlet.http. ttpservletresponse. Generally, the object response is used with cookies. The response object is also used with HTTP Headers.

Session object in jsp

The session object has a scope of an entire HttpSession. It is an instance of the javax.servlet.http.HttpSession class. It represents the session created for the requesting client, and stores objects between client's requests. The session object views and manipulates session information, such as the session identifier, creation time, and last accessed time. It also binds objects to a session, so that the user information may persist across multiple user connections.

The session object is valid only for HTTP requests.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 object Session is of type Javax.servlet.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 when there are multiple page requests.

jsp Out object

This denotes the Output stream in the context of page. The class or the interface name of the Out object is jsp.JspWriter. The Out object is written: Javax.servlet.jsp.JspWriter. The out object has a page scope. It is an instance of the javax.servlet.jsp.JspWriter class. The JspWriter class is the buffered version of the Printwriter class. It represents the output stream opened back to the client and provides the access to handle servlet's output stream.

jsp PageContext object

This is used to access page attributes and also to access all the namespaces associated with a JSP page. The lass or the interface name of the object PageContext is jsp.pageContext. The object PageContext is written: Javax.servlet.jsp.pagecontext The PageContext object has a page scope. It is an instance of the javax.servlet.jsp.PageContext class. It encapsulates the page-context for the particular JSP page. A pageContext instance provides access to all the namespaces associated with a JSP page. It also provides access to several page attributes such as to include some static or dynamic resource. Implicit objects are added to the PageContext automatically.

jsp Page object

The Page object denotes the JSP page, used for calling any instance of a Page's servlet. The class or the interface name of the Page object is jsp.HttpJspPage. The Page object is written: Java.lang.Object.

jsp Application object

The application object has an application scope. It is an instance of the javax.servlet.ServletContext class. It represents the context within which the JSP is executing. It defines a set of methods that a servlet uses to communicate with its servlet container. These functions include getting the MIME type, request dispatching, and writing contents to a log file. It allows the Web components in the JSP page in the application to share information. This is used to share the data with all application pages. The class or the interface name of the Application object is ServletContext. The Application object is written: Javax.servlet.http.ServletContext.

jsp config object

The config object has a page scope. It is an instance of the javax.servlet.ServletConfig class. The ServletConfig parameter can be set up in the web.xml inside the element. It uses the getInitParameter(String param) to obtain initialization parameters and the getServletContext() method to obtain the ServletContext object. This is used to get information regarding the Servlet configuration, stored in the Config object. The class or the interface name of the Config object is ServletConfig. The object Config is written Javax.servlet.http.ServletConfig.

jsp implicit object exception

The exception object has a page scope. It is an instance of the java.lang.Throwable class. It refers to the runtime exception that resulted in the error-page being invoked. This is available only in an error page, i.e., a page that has isErrorPage=true in the page directive.