The document discusses Java filters, including the filter API, configuring filters in web.xml, and different dispatcher types. It provides code examples of a sample LoggingFilter class that implements the Filter interface. Filters can be used to log requests, perform authentication, authorization, and other cross-cutting concerns. Filters are configured in web.xml and can apply to specific URLs or servlets, and different dispatcher types determine when filters are invoked for requests, forwards, includes, or errors.

1. Java/J2EE Programming Training
Java Filters

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Agenda
• Filter API
• Configuring filter
• DISPATCHER

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CROSSCUTTING
CONCERNS

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Filter API

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public class LoggingFilter implements Filter{
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("init method");
}
@Override
public void doFilter(ServletRequest request, ServletResponse
response, FilterChain chain) throws IOException, ServletException {
System.out.println("before dispatching request to servlet");
chain.doFilter(request, response);
System.out.println("After dispatching response from servlet");
}
@Override
public void destroy() {
System.out.println("Clean up resources");
}
}

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public class LoggingFilter implements Filter{
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("init method");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain
chain) throws IOException, ServletException {
System.out.println("before dispatching request to servlet");
chain.doFilter(request, response);
System.out.println("After dispatching response from servlet");
}
@Override
public void destroy() {
System.out.println("Clean up resources");
}
}

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Configuring filter
<filter>
<description>filter to log incoming request</description>
<filter-name>logFilter</filter-name>
<filter-class>com.example.filters.LoggingFilter</filter-class>
</filter>
URL PATTERN
<filter-mapping>
<filter-name>logFilter</filter-
name>
<url-pattern>/</url-pattern>
</filter-mapping>
SERVLET NAME
<filter-mapping>
<filter-name>logFilter</filter-name>
<servlet-name>TestServlet</servlet-
name>
</filter-mapping>

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Configuring filter
<filter>
<description>filter to log incoming request</description>
<filter-name>logFilter</filter-name>
<filter-class>com.example.filters.LoggingFilter</filter-class>
</filter>
URL PATTERN
<filter-mapping>
<filter-name>logFilter</filter-name>
<url-pattern>/</url-pattern>
</filter-mapping>
SERVLET NAME
<filter-mapping>
<filter-name>logFilter</filter-name>
<servlet-name>TestServlet</servlet-
name>
</filter-mapping>

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<servlet-mapping>
<servlet-name>UpdateAccounts</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
<filter-mapping>
<filter-name>authenticationFilter</filter-name>
<servlet-name>UpdateAccounts</servlet-name>
</filter-mapping>
<filter-mapping>
<filter-name>Authorization</filter-name>
<servlet-name>UpdateAccounts</servlet-name>
</filter-mapping>
<filter-mapping>
<filter-name>logFilter</filter-name>
<url-pattern>/</url-pattern>
</filter-mapping>
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DISPATCHER
RequestDispatcher rd =request.getRequestDispatcher(“UpdateAccounts”);
rd.forward( request, response );
• <filter-mapping>
• <filter-name>authenticationFilter</filter-name>
• <servlet-name>UpdateAccounts</servlet-name>
• <dispatcher>FORWARD</dispatcher>
• </filter-mapping>

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<filter-mapping>
<filter-name>loggingFilter</filter-name>
<servlet-name>UpdateAccounts</servlet-
name>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>

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update
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<filter-mapping>
<filter-name>audit</filter-name>
<servlet-
name>UpdateAccounts</servlet-name>
<dispatcher>INCLUDE</dispatcher>
</filter-mapping>
admin
RequestDispatcher rd
=request.getRequestDispatcher(“UpdateAccount”);
rd.include ( request,response );

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<filter-mapping>
<filter-name>audit</filter-name>
<servlet-name>UpdateAccounts</servlet-name>
<dispatcher>FORWARD</dispatcher>
</filter-mapping>
admin
RequestDispatcher rd =request.getRequestDispatcher(“UpdateAccount”);
rd.forward( request,response );

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update
Accounts
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<filter-mapping>
<filter-name>audit</filter-name>
<servlet-
name>UpdateAccounts</servlet-name>
<dispatcher>ERROR</dispatcher>
</filter-mapping>
admin
RequestDispatcher rd
=request.getRequestDispatcher(“UpdateAccount”);
rd.forward( request,response );

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Thank You