I’d like the ability to modify/configure filters in a different way than web.xml. Here is a static configuration of 2 filters. I’d like the ability to have one filter statically configured and allow that filter to load additional filters. I just wanted to know if anyone knows of lib that already has this.
Using Servlet API 2.5
<web-app> ... <filter> <filter-name>MyFilter1</filter-name> <filter-class>com.me.MyFilter1</filter-class> </filter> <filter-mapping> <filter-name>MyFilter1</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> ... <filter> <filter-name>MyFilter2</filter-name> <filter-class>com.me.MyFilter2</filter-class> </filter> <filter-mapping> <filter-name>MyFilter2</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> ... </web-app>
I’ve seen this done in Guice with GuiceFilter where the Filters are configured at runtime.
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Answer
Just do the same job as the container already does. I.e. reinvent the wheel of the chain of responsibility design pattern as is under the covers been used by servlet filters.
public class GodFilter implements Filter { private Map<Pattern, Filter> filters = new LinkedHashMap<Pattern, Filter>(); @Override public void init(FilterConfig config) throws ServletException { Filter1 filter1 = new Filter1(); filter1.init(config); filters.put(new Pattern("/foo/*"), filter1); Filter2 filter2 = new Filter2(); filter2.init(config); filters.put(new Pattern("*.bar"), filter2); // ... } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException { HttpServletRequest hsr = (HttpServletRequest) request; String path = hsr.getRequestURI().substring(hsr.getContextPath().length()); GodFilterChain godChain = new GodFilterChain(chain); for (Entry<Pattern, Filter> entry : filters.entrySet()) { if (entry.getKey().matches(path)) { godChain.addFilter(entry.getValue()); } } godChain.doFilter(request, response); } @Override public void destroy() { for (Filter filter : filters.values()) { filter.destroy(); } } }
with those little helper classes (which can if necessary be made private static
nested classes of the above GodFilter
):
public class Pattern { private int position; private String url; public Pattern(String url) { this.position = url.startsWith("*") ? 1 : url.endsWith("*") ? -1 : 0; this.url = url.replaceAll("/?\*", ""); } public boolean matches(String path) { return (position == -1) ? path.startsWith(url) : (position == 1) ? path.endsWith(url) : path.equals(url); } }
and
public class GodFilterChain implements FilterChain { private FilterChain chain; private List<Filter> filters = new ArrayList<Filter>(); private Iterator<Filter> iterator; public GodFilterChain(FilterChain chain) { this.chain = chain; } @Override public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException { if (iterator == null) { iterator = filters.iterator(); } if (iterator.hasNext()) { iterator.next().doFilter(request, response, this); } else { chain.doFilter(request, response); } } public void addFilter(Filter filter) { if (iterator != null) { throw new IllegalStateException(); } filters.add(filter); } }
You could if necessary also feed a XML config file with all possible filters so that you end up with easier configuration. You could use reflection to create filters in init()
of your GodFilter
.
Oh nevermind, that’s what the web.xml
and the container already is doing…