Servlet API

Servlet API is a set of classes and interfaces that specify a contract between a servlet class and a servlet container. Some examples of servers that provide servlet containers are: Apache Tomcat, Oracle’s WebLogic, IBM’s Websphere, JBoss etc. All the API classes and interfaces are grouped into following packages:

• javax.servlet
• javax.servlet.http

 

javax.servlet Package

 

Provides a set of classes and interfaces that describe and defined the contract between the servlet class and the runtime environment provided by the servlet container. Following are the interfaces available in this package:

 

 

Following are the classes available in this package:

 

 

Following are the exception classes available in this package:

 

 

javax.servlet.http Package

 

Provides a set of classes and interfaces that describe and define the contract between the servlet class running under the HTTP protocol and the runtime environment provided by the servlet container. HttpServlet class implements the Servlet interface.

 

Following are the interfaces available in this package:

 

 

Following are the classes available in this package:

 

 

javax.servlet.Servlet Interface

 

The Servlet interface provides a standard abstraction for the servlet container to understand the servlet object created by the user. Following are the methods available in this interface:

• void init(ServletConfig config)
• void service(ServletRequest req, ServletResponse res)
• void destroy()
• ServletConfig getServletConfig()
• String getServletInfo()

 

javax.servlet.ServletConfig Interface

 

The ServletConfig interface provides a standard abstraction for the servlet object to get environment details from the servlet container. Container implementing the ServletConfig object supports the following operations:

• Retrieve the initialization parameters from xml file.
• Retrieve the ServletContext object that describes the application’s runtime environment.
• Retrieve the servlet name as configured in xml.

 

HttpServletRequest Interface

 

The HttpServletRequest interface is a subtype of ServletRequest interface. Implementation for this interface is provided by the servlet container. The HttpServletRequest interface object allows us to access the data available in the HTTP headers and HTTP requests. Following methods helps us to access the header information:

• String getHeader(String)
• Enumeration getHeaders(String)
• Enumeration getHeaderNames()

 

Following methods helps us to access the path information:

• String getContextPath()
• String getServletPath()
• String getPathInfo()
• String getRequestURI()

 

HttpServletResponse Interface

 

The HttpServletResponse is a subtype of ServletResponse interface. Implementation for this interface is provided by the servlet container. The HttpServletResponse interface object let’s us to specify information that will be a part of the HTTP response headers or the HTTP response. Following methods helps us to manipulate the HTTP response headers:

• addHeader(String name, String value)
• containsHeader(String name)
• setHeader(String name, String value)
• setDateHeader(String name, long date)
• addIntHeader(String name, int value)
• addDateHeader(String name, long date)

 

Following table shows some of the header fields and the description of their value:

 

 

Other methods provided by this interface are:

• sendError(int)
• sendError(int, String)
• sendRedirect(String URL)

 

After the sendError() method is invoked, we cannot send any response messages to the client.