This document discusses servlets, servlet filters, and URL rewriting in Java web applications. It defines servlets and servlet configuration using web.xml, and explains how to get initialization parameters from the servlet config and servlet context. It also describes what servlet filters are used for, the types of filters, and the main filter methods. Finally, it provides an example of a log filter implementation and discusses URL rewriting by appending tokens or parameters to URLs.

1. Advance Java Technology
[Servlet]
Mali Nayan M
Assistant Professor
Department of Information Technology
Sigma Institute of Engineering
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2. <context-param>
<param-name>collegename</param-name>
<param-value>sigmainstituteofengineering</param-value>
</context-param>
<servlet>
<servlet-name>ServletConfigTest</servlet-name>
<servlet-class>com.javapapers.ServletConfigTest</servlet-class>
<init-param>
<param-name>departmentname</param-name>
<param-value>informationtechnology</param-value>
</init-param>
</servlet>
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web.xml

3. ServletConfig
• ServletConfig is implemented by the servlet container to initialize a
single servlet using init(). That is, you can pass initialization
parameters to the servlet using the web.xml deployment descriptor
ServletConfig sc = getServletConfig();
sc. getInitParameter(“departmentname”);
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4. ServletContext
• public interface ServletContext
ServletContext is implemented by the servlet container for all
servlet to communicate with its servlet container
• this is like a application global variable mechanism for a single web
application deployed in only one JVM.
ServletContext sc = getServletContext();
out.print("<br>country name is " + sc.getInitParameter("collegename"));
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5. Filters
Servlet Filters are Java classes that can be used in Servlet Programming
for the following purposes:
• To intercept requests from a client before they access a resource at
back end.
• To manipulate responses from server before they are sent back to the
client.
• When the web container starts up your web application, it creates an
instance of each filter that you have declared in the deployment
descriptor. The filters execute in the order that they are declared in
the deployment descriptor.
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6. Types of Filters
• Authentication Filters.
• Data compression Filters.
• Encryption Filters.
• Filters that trigger resource access events.
• Image Conversion Filters.
• Logging and Auditing Filters.
• MIME-TYPE Chain Filters.
• Tokenizing Filters .
• XSL/T Filters That Transform XML Content.
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7. 1 public void doFilter (ServletRequest, ServletResponse, FilterChain)
This method is called by the container each time a request/response pair is
passed through the chain due to a client request for a resource at the end of the
chain.
2 public void init(FilterConfig filterConfig)
This method is called by the web container to indicate to a filter that it is being
placed into service.
3 public void destroy()
This method is called by the web container to indicate to a filter that it is being
taken out of service.
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8. web.xml
<filter>
<filter-name>LogFilter</filter-name>
<filter-class>LogFilter</filter-class>
<init-param>
<param-name>test-param</param-name>
<param-value>Initialization Paramter</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>LogFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
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9. public class LogFilter implements Filter {
public void init(FilterConfig config) throws ServletException{
String testParam = config.getInitParameter("test-param");
System.out.println("Test Param: " + testParam);
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws java.io.IOException, ServletException {
String ipAddress = request.getRemoteAddr();
System.out.println("IP "+ ipAddress + ", Time " + new Date().toString());
chain.doFilter(request,response);
}
public void destroy( ){
}
}
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10. URL Rewriting
• In URL rewriting, we append a token or identifier to the URL of the
next Servlet or the next resource. We can send parameter
name/value pairs using the following format:
url?name1=value1&name2=value2&??
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