how to change the requestURL using filter or servlet

Question

how to change the requestURL using filter or servlet .

for example if request is "http://servername1:8080" I want to change the same to "http://servername2:7001"

Answer 1

Add the following servlet filter to your application:

public class RequestUrlRewritingFilter implements Filter {

    //Empty init()/destroy() here

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        final HttpServletRequestWrapper wrapped = new HttpServletRequestWrapper(request) {
            @Override
            public StringBuffer getRequestURL() {
                final StringBuffer originalUrl = ((HttpServletRequest) getRequest()).getRequestURL();
                return new StringBuffer("http://servername2:7001");
            }
        };
        chain.doFilter(wrapped, response);
    }
}

All requests you want to intercept must go through it. As you can see it takes original request method and overrides getRequestURL() method by returning a different value. You still have access to the original request if you want to base new URL on the old one.

At the end you must continue processing the request chain.doFilter() but by providing wrapped request, not the original one.

Answer 2

The above is a good solution compared to many others on the web that use .forward() as that breaks the filter chain. This solution allows subsequent filters to process the request after is has been modified.

But there are 2 additional methods that must implemented in order for this to be 'transparent' to downstream filter processing, and they must present the same modification of the URL to present a consistent request object. The wrapper must implement:

@Override
public String getRequestURI() {
    final String originalUri = ((HttpServletRequest)getRequest()).getRequestURI();
    return "/"; // Must be consistent with getRequestURL()
}
@Override
public String getServletPath() {
    final String originalPath = ((HttpServletRequest)getRequest()).getServletPath();
    return "/"; // Must be consistent with getRequestURL()
}