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The Servlet Context
A Web application includes many parts. It is more than just one servlet or JSP. Numerous JSPs and one or more Servlets and other supporting java classes together form the web application. To help manage an application, you will sometimes need to set and get information that all of the servlets share together, which we will refer to as context-wide.
For Example, if you want a single name using which you can refer to the application, you can set it in the servlet context and have it shared across all instances that use the application.
Ex Code:
public void init(ServletConfig config) throws ServletException
{
super.init(config);
// Get the Context
ServletContext context =config.getServletContext();
// Set the attribute
context.setAttribute("appName", "My Test App");
}
Any time you want, you can refer to this attribute in the context and get its value like below:
String appName = context.getAttribute("appName");
After the above line of code, the variable appName will have the value "My Test App
Wiki User
∙ 13y ago
The ServletContext is an object provided by the servlet container that allows servlets to communicate with the container. It represents the configuration and environment of a web application and provides access to resources such as parameters, attributes, and initialization parameters. Servlets can use the ServletContext to perform tasks like accessing resources, logging events, and managing session persistence.
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How do you get servlet context instance to servlet?
You can get the ServletContext instance in a servlet by using the getServletContext() method provided by the HttpServlet class, which is the base class for servlets. This method returns the ServletContext object associated with the servlet. For example: ServletContext context = getServletContext();
What is the difference between servlet context page context?
ServletContext is an interface for communication with the servlet container while PageContext is an object for managing data related to a JSP page. ServletContext is used for application-wide resources while PageContext is specific to a single JSP page.
How do you get the image file from the database with JSP?
You can retrieve an image file from a database in JSP by writing a servlet that fetches the image from the database and streams it to the JSP page. The servlet will set the content type to "image/jpeg" or the appropriate image format and write the image data to the response output stream. In the JSP page, you can then display the image by setting the source attribute of the img tag to the servlet URL.
How do you dynamically identify the jsp in servlet?
You can dynamically identify the JSP file in a servlet by using the request URL or request parameters to determine which JSP to forward the request to. You can also store necessary information in session attributes or external configurations to help determine the appropriate JSP to display. Finally, you can use a servlet mapping or URL pattern to route requests to different JSP files based on the URL.
What is Servlet API used for connecting database?
The Servlet API is not specifically used for connecting to databases. Instead, servlets typically interact with databases through JDBC (Java Database Connectivity), which is a standard Java API for database access. Servlets can use JDBC to establish connections, execute SQL queries, and retrieve results from a database.
How do you get ServletContext object in EJB - 38k?
get servlet context path from EJB
How do you get servlet context instance to servlet?
You can get the ServletContext instance in a servlet by using the getServletContext() method provided by the HttpServlet class, which is the base class for servlets. This method returns the ServletContext object associated with the servlet. For example: ServletContext context = getServletContext();
What is the difference between servlet context page context?
ServletContext is an interface for communication with the servlet container while PageContext is an object for managing data related to a JSP page. ServletContext is used for application-wide resources while PageContext is specific to a single JSP page.
Which method is used to retrive an initialitation parameters from a servlet context?
ServletContext sc=getServletContext(); String s=sc.getInitParameter();
What are types of servlet?
Http servlet and Generic servlet
What is java servlet chaining?
Servlet Chaining means the output of one servlet act as a input to another servlet. Servlet Aliasing allows us to invoke more than one servlet in sequence when the URL is opened with a common servlet alias. The output from first Servlet is sent as input to other Servlet and so on. The Output from the last Servlet is sent back to the browser. The entire process is called Servlet Chaining.
How many interfaces in a java servlet package?
The javax.servlet package defines 12 interfaces, 7 classes, and 2 exceptions. The Interfaces are as follows:• Filter:- Preprocessor of the request before it reaches a servlet. It can also be a postprocessor of the response leaving a servlet. It can modify a request or response (for example, change headers), the request to a resource (a servlet or static content), or the response from a resource.• RequestDispatcher:- This is the servlet version of a redirect. It enables requests to be processed and then forwarded to other components of a Web application, such as another servlet, HTML file, or JSP file.• Servlet:- Defines the life-cycle methods that are implemented by all servlets.• ServletConfig:- This class has the methods for accessing the servlet configuration information such as the servlets name (from the web.xml file), the initialization parameters, and the ServletContext object.• ServletContext:- These methods enable your servlet to communicate with its servlet container. This is how you get the MIME type of a file, dispatch requests, or write to a log file. Notice that this information has application scope. The most important features of the ServletContext are application-scope attributes access, logging, and context initialization parameters.• ServletContextAttributeListener:- Implementations of this interface receive notifications of changes to the attribute list on the servlet context of a Web application. Supports the handling of the ServletContextAttributeEvent class.• ServletContextListener:- An interface that supports the handling of the ServletContextEvent class. Defines a set of methods that a servlet uses to communicate with its servlet container. It can get the MIME type of a file, dispatch requests, or write to a log file. Notice that there is one context per "Web application" per Java Virtual Machine. The specification defines a "Web application" as a collection of servlets and content installed under a specific subset of the server's URL namespace, such as /catalog, and possibly installed via a .war file.• ServletRequest:- This interface forms the base for the class that provides client request information to a servlet. It is protocol-independent.• ServletResponse:- This interface forms the base for the class that represents the response sent from the servlet to the client.• SingleThreadModel:- An interface that ensures a given servlet handles only one request at a time.
Can insert javascript coding in servlet?
No. Javascript code can be present inside a JSP but not inside a servlet. A Servlet is a pure java class.
What are the servlet config methods?
Methods in the Servlet ContextApart from setting and getting custom attributes used for our application, the context also contains various methods that we can use to retrieve specific information about the application and other aspects. They are:• getAttributeNames() - Returns an Enumeration object containing the attribute names available within this servlet context.• getContext(String uripath) - Returns a ServletContext object that corresponds to a specified URL on the server.• getInitParameter(String name) - Returns a string containing the value of the named context-wide initialization parameter, or null if the parameter does not exist.• getInitParameterNames() - Returns the names of the context's initialization parameters as an Enumeration of string objects, or an empty Enumeration if the context has no initialization parameters.• getMajorVersion() - Returns the major version as an int of the Java Servlet API that this Servlet Container supports.• getMimeType(java.lang.String file) - Returns the MIME type as a string of the specified file, or null if the MIME type is not known.• getMinorVersion() - Returns the minor version as an int of the Servlet API that this Servlet Container supports.• getNamedDispatcher(String name) Returns a RequestDispatcher object that acts as a wrapper for the named servlet.• getRealPath(String path) - Returns a string containing the real path for a given virtual path.• getRequestDispatcher(String path) Returns a RequestDispatcher object that acts as a wrapper for the resource located at the given path.• getResource(String path) - Returns a URL to the resource that is mapped to a specified path.• getResourceAsStream(String path) - Returns the resource located at the named path as an InputStream object.• getServerInfo() Returns the name and version as a String of the Servlet Container on which the servlet is running.
What is servlet mapping?
A Servlet Mapping is a directive in the web.xml that tells the Servlet Container which class to use when a particular Servlet is called. A Servlet is a class within your Java Web Application. Let's say you have a servlet called MyServlet in the com.example.servlet package. You would need to have a Servlet Mapping pointing the path "/MyServlet" to the "com.example.servlet.MyServlet" class. Without the servlet mapping, you would not be able to invoke your servlet because the Servlet container would not know where it is. JSPs are different - they do not need mappings like this. JSPs exist within the WebRoot of the application, so they are always available. Servlets exist in the WEB-INF\Classes directory once your application is deployed.
How the pass value from the HTML pages to the servlet?
You need a form to pass value to a servlet. In the form tag, the action element passes the value into the servlet.
How does Apache httpd work?
Tomcat is a servlet container, and the following is how a servlet container works The init, service, and destroy methods are the servlet's lifecycle methods. The init method is called once by the servlet container after the servlet class has been instantiated to indicate to the servlet that it being placed into service. The init method must complete successfully before the servlet can receive any requests. A servlet programmer can override this method to write initialization code that needs to run only once, such as loading a database driver, initializing values, and so on. In other cases, this method is normally left blank. The service method is then called by the servlet container to allow the servlet to respond to a request. The servlet container passes a javax.servlet.ServletRequest object and a javax.servlet.ServletResponse object. The ServletRequest object contains the client's HTTP request information and the ServletResponse encapsulates the servlet's response. These two objects enable you to write custom code that determines how the servlet services the client request. The servlet container calls the destroy method before removing a servlet instance from service. This normally happens when the servlet container is shut down or when the servlet container needs some free memory. This method is called only after all threads within the servlet's service method have exited or after a timeout period has passed. After the servlet container calls destroy, it will not call the service method again on this servlet. The destroy method gives the servlet an opportunity to clean up any resources that are being held (for example, memory, file handles, and threads) and make sure that any persistent state is synchronized with the servlet's current state in memory. For Better Picture, Visit below article full of images to clear the concept : http://shivasoft.in/blog/java/servlet/how-container-handles-the-servlet-request/
