This document provides an overview of filters in Java servlets. Filters intercept requests and responses between clients and servlets/JSPs. Filters are configured in web.xml and implement init(), doFilter(), and destroy() methods. Filters can manipulate requests and responses using wrappers and operate in a filter chain. Servlets can communicate by forwarding requests or including output from one servlet in another.

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Filters Inter-Servlet Communication

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Objectives
 Introduction to Filters
 Filter API
 Configuring Filter
 Manipulating Request and Responses
 Servlet Communication

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Introduction Filter

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Filters
 Components that add functionality to the
request and response processing of a
Web Application
 Intercept the requests and responses that
flow between a client and a Servlet/JSP.

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Filter Participation
User Filter
Web Resource
(Servlet / JSP)
Request
Response
Filter Participating in Request-Response Process

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Filter Life Cycle
Instantiation
and Loading
Initialization
init()
doFilter()
destroy()
Unavailable
GC

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Filter Chain
 Invoke a series of filters
 If the Calling filter is last filter, will invoke web resource
Filter
1
Client
Filter
2
Filter
3
Web
Resourc
e
Working of Filter Chain
Filter Chain

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Usage of Filter
 Authentication
 Logging and auditing filter
 Image conversion filters
 Data compression
 Encryption filters
 Filters that trigger resource access events

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Benefits of Filter

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Compress Filter

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Working of Filter

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Working of Filter

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Filter API

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“Filter” Interface
A filter is an object than perform filtering tasks
on either the request to a resource (a
servlet or static content), or on the response
from a resource, or both.
 Init()
 doFilter()
 Destroy()

15. Slide 15 of 25
“FilterConfig” Interface
 A filter configuration object used by a servlet
container used to pass information to a filter
during initialization
 Methods
– getFilterName()
– getInitParameter()
– getInitParameterNames()
– getServletContext()

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“FilterChain” Interface
 A FilterChain is an object provided by the
servlet container to the developer giving a
view into the invocation chain of a filtered
request for a resource
 Methods
– doFilter()

17. Slide 17 of 25
Configuring Filter
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<filter>
<filter-name>TimerFilter</filter-name>
<filter-class>filters.TimerFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>TimerFilter</filter-name>
<url-pattern>/TimerFilter</url-pattern>
</filter-mapping>
<session-config>
<session-timeout>
30
</session-timeout>
</session-config>
<welcome-file-list>
<welcome-file>Timer.html</welcome-file>
</welcome-file-list>
</web-app>
17

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Filter Element
 <icon>
 <filter-name>
 <display-name>
 <description>
 <filter-class>
 <init-param>

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Filter-Mapping Element
 <filter-name>
 <url-name>
 <servlet-name>

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Configuring Filter Chain

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Manipulating Request and Response

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Manipulating Request and Response
 ServletRequestWrapper
 ServletResponseWrapper

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Inter-Servlet Communication
 A process where two or more Servlets
communicates with each other to process
the client request.
 A Servlet can forward the request to
another Servlet to process the client
request.
 A Servlet can include the output of another
Servlet to process the client request.

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Applet – Servlet Communication
 Developing Applet front end application
 Establishing connection between applet and
servlet
 Communicasting throught object
serialisation
 Sending objects from applet to servlet
 Sending objects from servlet to applet

25. Slide 25 of 25
Summary
 Introduction to Filters
 Filter API
 Configuring Filter
 Manipulating Request and Responses
 Servlet Communication