SPR-8585: add generic composite filter

org.springframework.web/src/main/java/org/springframework/web/filter/CompositeFilter.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2002-2011 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.filter;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+
+/**
+ * A generic composite servlet {@link Filter} that just delegates its behaviour to a chain (list) of user supplied
+ * filters, achieving the functionality of a {@link FilterChain}, but conveniently using only {@link Filter} instances.
+ * This is useful for filters that require dependency injection, and can therefore be set up in a Spring application
+ * context. Typically this composite would be used in conjunction with {@link DelegatingFilterProxy}, so that it can be
+ * declared in Spring but applied to a servlet context.
+ * 
+ * @since 3.1
+ * 
+ * @author Dave Syer
+ * 
+ */
+public class CompositeFilter implements Filter {
+
+	private List<? extends Filter> filters = new ArrayList<Filter>();
+
+	public void setFilters(List<? extends Filter> filters) {
+		this.filters = new ArrayList<Filter>(filters);
+	}
+
+	/**
+	 * Clean up all the filters supplied, calling each one's destroy method in turn, but in reverse order.
+	 * 
+	 * @see Filter#init(FilterConfig)
+	 */
+	public void destroy() {
+		for (int i = filters.size(); i-- > 0;) {
+			Filter filter = filters.get(i);
+			filter.destroy();
+		}
+	}
+
+	/**
+	 * Initialize all the filters, calling each one's init method in turn in the order supplied.
+	 * 
+	 * @see Filter#init(FilterConfig)
+	 */
+	public void init(FilterConfig config) throws ServletException {
+		for (Filter filter : filters) {
+			filter.init(config);
+		}
+	}
+
+	/**
+	 * Forms a temporary chain from the list of delegate filters supplied ({@link #setFilters(List)}) and executes them
+	 * in order. Each filter delegates to the next one in the list, achieving the normal behaviour of a
+	 * {@link FilterChain}, despite the fact that this is a {@link Filter}.
+	 * 
+	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
+	 */
+	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
+			ServletException {
+		new VirtualFilterChain(chain, filters).doFilter(request, response);
+	}
+
+	private static class VirtualFilterChain implements FilterChain {
+		private final FilterChain originalChain;
+		private final List<? extends Filter> additionalFilters;
+		private int currentPosition = 0;
+
+		private VirtualFilterChain(FilterChain chain, List<? extends Filter> additionalFilters) {
+			this.originalChain = chain;
+			this.additionalFilters = additionalFilters;
+		}
+
+		public void doFilter(final ServletRequest request, final ServletResponse response) throws IOException,
+				ServletException {
+			if (currentPosition == additionalFilters.size()) {
+				originalChain.doFilter(request, response);
+			} else {
+				currentPosition++;
+				Filter nextFilter = additionalFilters.get(currentPosition - 1);
+				nextFilter.doFilter(request, response, this);
+			}
+		}
+
+	}
+
+}

org.springframework.web/src/test/java/org/springframework/web/filter/CompositeFilterTests.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2004, 2005 Acegi Technology Pty Limited
+ * Copyright 2006-2011 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.filter;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+
+import org.junit.Test;
+import org.springframework.mock.web.MockFilterConfig;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.mock.web.MockServletContext;
+
+/**
+ * @author Dave Syer
+ */
+public class CompositeFilterTests {
+
+	@Test
+	public void testCompositeFilter() throws ServletException, IOException {
+		ServletContext sc = new MockServletContext();
+
+		MockFilter targetFilter = new MockFilter();
+
+		MockFilterConfig proxyConfig = new MockFilterConfig(sc);
+
+		CompositeFilter filterProxy = new CompositeFilter();
+		filterProxy.setFilters(Arrays.asList(targetFilter));
+		filterProxy.init(proxyConfig);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		filterProxy.doFilter(request, response, null);
+
+		assertNotNull(targetFilter.filterConfig);
+		assertEquals(Boolean.TRUE, request.getAttribute("called"));
+
+		filterProxy.destroy();
+		assertNull(targetFilter.filterConfig);
+	}
+
+
+	public static class MockFilter implements Filter {
+
+		public FilterConfig filterConfig;
+
+		public void init(FilterConfig filterConfig) throws ServletException {
+			this.filterConfig = filterConfig;
+		}
+
+		public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
+			request.setAttribute("called", Boolean.TRUE);
+		}
+
+		public void destroy() {
+			this.filterConfig = null;
+		}
+	}
+
+}