javax.servlet.Filter intercepts a request and manupulates a ServletRequest object or a ServletResponse object.
e.g.
・Filter can intercepts a request to the application and encode a string.
・Total management using Filters
web.xml definition
You have to define filters on the web.xml.
e.g.
<filter>
<filter-name>MyFilter</filter-name>
<filter-class>filter.MyFilter</filter-class>
<init-param>
<param-name>EncodeName</param-name>
<param-value>Shift_JIS</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>MyFilter</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>
filter-name : The name of the Filter class
fiter-class : The fully qualified name of the Filter class
init-param : Initial parameter. It can be reached by FilterConfig.
url-pattern : Specifies the URL. An asterisk (*) can be used.
dispatcher : Specifies REQUEST,FORWARD,INCLUDE,ERROR. The default is REQUEST.
Methods in the Filter interface
public void init(FilterConfig config)
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain chain)
public void destroy()
＜Sample＞
public class MyFilter1 {
private FilterConfig config = null;
public void init(FilterConfig config) throws ServletException {
this.config = config;
}
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest)req;
String url = request.getRequestURI();
/* Do something, for example, counting up in a database */
/* to the next filter */
chain.doFilter(req,res);
}
public void destroy() {}
}
<filter>
<filter-name>MyFilter1</filter-name>
<filter-class>filter.MyFilter1</filter-class>
</filter>
<filter-mapping>
<filter-name>MyFilter1</filter-name>
<url-pattern>/MyFilter1</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>
<dispatcher>INCLUDE</dispatcher>
<dispatcher>ERROR</dispatcher>
</filter-mapping>
