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copied!<ol> <li>Implement <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/Filter.html" rel="noreferrer"><code>javax.servlet.Filter</code></a>.</li> <li>In <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/Filter.html#doFilter%28javax.servlet.ServletRequest,%20javax.servlet.ServletResponse,%20javax.servlet.FilterChain%29" rel="noreferrer"><code>doFilter()</code></a> method, cast the incoming <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/ServletRequest.html" rel="noreferrer"><code>ServletRequest</code></a> to <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletRequest.html" rel="noreferrer"><code>HttpServletRequest</code></a>.</li> <li>Use <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletRequest.html#getRequestURI%28%29" rel="noreferrer"><code>HttpServletRequest#getRequestURI()</code></a> to grab the path.</li> <li>Use straightforward <a href="http://docs.oracle.com/javase/6/docs/api/java/lang/String.html" rel="noreferrer"><code>java.lang.String</code></a> methods like <a href="http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#substring%28int%29" rel="noreferrer"><code>substring()</code></a>, <a href="http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#split%28java.lang.String%29" rel="noreferrer"><code>split()</code></a>, <a href="http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#concat%28java.lang.String%29" rel="noreferrer"><code>concat()</code></a> and so on to extract the part of interest and compose the new path.</li> <li>Use either <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/ServletRequest.html#getRequestDispatcher%28java.lang.String%29" rel="noreferrer"><code>ServletRequest#getRequestDispatcher()</code></a> and then <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/RequestDispatcher.html#forward%28javax.servlet.ServletRequest,%20javax.servlet.ServletResponse%29" rel="noreferrer"><code>RequestDispatcher#forward()</code></a> to forward the request/response to the new URL (server-side redirect, not reflected in browser address bar), <strong>or</strong> cast the incoming <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/ServletResponse.html" rel="noreferrer"><code>ServletResponse</code></a> to <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletResponse.html" rel="noreferrer"><code>HttpServletResponse</code></a> and then <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletResponse.html#sendRedirect%28java.lang.String%29" rel="noreferrer"><code>HttpServletResponse#sendRedirect()</code></a> to redirect the response to the new URL (client side redirect, reflected in browser address bar).</li> <li>Register the filter in <code>web.xml</code> on an <code>url-pattern</code> of <code>/*</code> or <code>/Check_License/*</code>, depending on the context path, or if you're on Servlet 3.0 already, use the <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/annotation/WebFilter.html" rel="noreferrer"><code>@WebFilter</code></a> annotation for that instead.</li> </ol> <p>Don't forget to add a check in the code if the URL <em>needs</em> to be changed and if <em>not</em>, then just call <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/FilterChain.html#doFilter%28javax.servlet.ServletRequest,%20javax.servlet.ServletResponse%29" rel="noreferrer"><code>FilterChain#doFilter()</code></a>, else it will call itself in an infinite loop.</p> <p>Alternatively you can also just use an existing 3rd party API to do all the work for you, such as <a href="http://tuckey.org/urlrewrite/" rel="noreferrer">Tuckey's UrlRewriteFilter</a> which can be configured the way as you would do with Apache's <code>mod_rewrite</code>.</p>

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