List and explain core classes and interfaces in the javax.servlet package.

7.A] List and explain core classes and interfaces in the javax.servlet package.

Answer:

INTERFACES	CLASSES
Servlet	ServletInputStream
ServletContext	ServletOutputStream
ServletConfig	ServletException
ServletRequest	UnavailableException
ServletResponse	GenericServlet

Interface Summary
Servlet	Defines methods that all servlets must implement.
ServletRequest	Defines an object to provide client request information to a servlet.
ServletResponse	Defines an object to assist a servlet in sending a response to the client.
ServletConfig	A servlet configuration object used by a servlet container to pass information to a servlet during initialization.
ServletContext	Defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.

Class Summary
GenericServlet	Defines a generic, protocol-independent servlet.
ServletInputStream	Provides an input stream for reading binary data from a client request, including an efficient readLine method for reading data one line at a time.
ServletOutputStream	Provides an output stream for sending binary data to the client.
ServletException	Defines a general exception a servlet can throw when it encounters difficulty.
UnavailableException	Defines an exception that a servlet or filter throws to indicate that it is permanently or temporarily unavailable.

Core Interfaces in javax.servlet

1. Servlet Interface

• Purpose: The fundamental interface that all servlets must implement. It provides the methods required for servlet lifecycle management and request handling.
• Key Methods:
• void init(ServletConfig config): Initializes the servlet with configuration parameters.
• void service(ServletRequest request, ServletResponse response): Handles requests and generates responses.
• void destroy(): Cleans up resources before the servlet is destroyed.
• ServletConfig getServletConfig(): Returns the servlet configuration.
• String getServletInfo(): Provides information about the servlet.

2. ServletRequest Interface

• Purpose: Provides methods to obtain request data and metadata from the client request.
• Key Methods:
• Object getAttribute(String name): Retrieves an attribute from the request.
• Enumeration<String> getAttributeNames(): Returns an enumeration of attribute names.
• String getParameter(String name): Retrieves a parameter from the request.
• Enumeration<String> getParameterNames(): Returns an enumeration of parameter names.
• BufferedReader getReader(): Retrieves the request body as a BufferedReader.

3. ServletResponse Interface

• Purpose: Defines methods for sending responses to the client.
• Key Methods:
• void setContentType(String type): Sets the MIME type of the response.
• PrintWriter getWriter(): Retrieves a PrintWriter to write response data.
• void setCharacterEncoding(String charset): Sets the character encoding for the response.
• void setContentLength(int len): Sets the length of the response content.

4. ServletConfig Interface

• Purpose: Provides configuration information to a servlet, such as initialization parameters.
• Key Methods:
• String getInitParameter(String name): Retrieves an initialization parameter.
• Enumeration<String> getInitParameterNames(): Returns an enumeration of initialization parameter names.
• ServletContext getServletContext(): Returns the servlet context.

5. ServletContext Interface

• Purpose: Provides a servlet with information about its environment and allows interaction with other servlets and web resources.
• Key Methods:
• String getContextPath(): Returns the context path of the web application.
• RequestDispatcher getRequestDispatcher(String path): Returns a RequestDispatcher for a given path.
• InputStream getResourceAsStream(String path): Retrieves a resource as an InputStream.
• void log(String msg): Writes a log message.

6. RequestDispatcher Interface

• Purpose: Allows forwarding a request to another resource or including the content of another resource in the response.
• Key Methods:
• void forward(ServletRequest request, ServletResponse response): Forwards the request to another resource.
• void include(ServletRequest request, ServletResponse response): Includes the content of another resource in the response.

Core Classes in javax.servlet

1. GenericServlet Class

• Purpose: Provides default implementations for the Servlet interface methods. It simplifies the development of servlets by handling common functionality.
• Key Methods:
• void service(ServletRequest req, ServletResponse res): Must be overridden by subclasses to handle requests.
• ServletConfig getServletConfig(): Returns the servlet configuration.

2. HttpServlet Class

• Purpose: Extends GenericServlet and provides additional methods specific to HTTP requests, such as handling GET, POST, PUT, and DELETE requests.
• Key Methods:
• void doGet(HttpServletRequest req, HttpServletResponse resp): Handles GET requests.
• void doPost(HttpServletRequest req, HttpServletResponse resp): Handles POST requests.
• void doPut(HttpServletRequest req, HttpServletResponse resp): Handles PUT requests.
• void doDelete(HttpServletRequest req, HttpServletResponse resp): Handles DELETE requests.

3. ServletInputStream Class

• Purpose: Provides an input stream for reading binary data from the client request, useful for processing binary data like files.
• Key Methods:
• int read(): Reads the next byte of data.
• int read(byte[] b): Reads bytes into an array.
• int read(byte[] b, int off, int len): Reads bytes into an array from a specified offset and length.

4. ServletOutputStream Class

• Purpose: Provides an output stream for sending binary data to the client, such as images or files.
• Key Methods:
• void write(int b): Writes a byte of data.
• void write(byte[] b): Writes an array of bytes.
• void write(byte[] b, int off, int len): Writes a portion of an array of bytes.

5. ServletException Class

• Purpose: Indicates a servlet-specific problem or error during request processing.
• Key Methods:
• Throwable getRootCause(): Returns the root cause of the exception.
• String getMessage(): Returns a detailed message about the exception.

6. UnavailableException Class

• Purpose: Signals that a servlet is temporarily unavailable and cannot handle requests at the moment.
• Key Methods:
• int getUnavailableSeconds(): Returns the number of seconds the servlet will be unavailable.
• String getMessage(): Returns a detailed message about the exception.

Summary

• Interfaces:
• Servlet: Base interface for all servlets.
• ServletRequest: Provides methods for request data.
• ServletResponse: Defines methods for sending responses.
• ServletConfig: Provides servlet configuration information.
• ServletContext: Provides context information and resource interaction.
• RequestDispatcher: Manages request forwarding and inclusion.
• Classes:
• GenericServlet: Convenience class for basic servlet functionality.
• HttpServlet: Handles HTTP-specific requests.
• ServletInputStream: Reads binary data from requests.
• ServletOutputStream: Sends binary data in responses.
• ServletException: Signals servlet errors.
• UnavailableException: Indicates temporary servlet unavailability.