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Thejavax.servlet
package provides interfaces and classes for writing servlets. The architecture of the package is described below.
The central abstraction in the Servlet API is the
Servlet
interface. All servlets implement this interface, either
directly or, more commonly, by extending a class that implements it such as
HttpServlet
The Servlet
interface declares, but does not implement,
methods that manage the servlet and its communications with clients.
Servlet writers provide some or all of these methods when developing a
servlet.
When a servlet accepts a call from a client, it receives two objects:
ServletRequest
, which encapsulates the communication from
the client to the server. ServletResponse
, which encapsulates the communication from
the servlet back to the client.
ServletRequest
and ServletResponse
are
interfaces defined by the javax.servlet
package.
The ServletRequest
interface allows the servlet access to:
ServletInputStream
. Servlets use the
input stream to get data from clients that use application protocols such
as the HTTP POST and PUT methods.
Interfaces that extend ServletRequest
interface allow the
servlet to retrieve more protocol-specific data. For example, the
HttpServletRequest
interface contains methods for accessing
HTTP-specific header information.
The ServletResponse
interface gives the servlet methods for
replying to the client. It:
ServletOutputStream
, and a
Writer
through which the servlet can send the reply data.
Interfaces that extend the ServletResponse
interface give
the servlet more protocol-specific capabilities. For example, the
HttpServletResponse
interface contains methods that allow the
servlet to manipulate HTTP-specific header information.
The classes and interfaces described above make up a basic Servlet. HTTP servlets have some additional objects that provide
session-tracking capabilities. The servlet writer can use these APIs to
maintain state between the servlet and the client that persists across
multiple connections during some time period. HTTP servlets also have
objects that provide cookies. The servlet writer uses the cookie API to
save data with the client and to retrieve this data.
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