SPR-4419: Shallow ETag support

2008-10-30 15:29:19 +00:00
parent 4f9fc753ca
commit a1545e3f06
2 changed files with 245 additions and 0 deletions
--- a/org.springframework.web/src/main/java/org/springframework/web/filter/ShallowEtagHeaderFilter.java
+++ b/org.springframework.web/src/main/java/org/springframework/web/filter/ShallowEtagHeaderFilter.java
@@ -0,0 +1,152 @@
+/*
+ * Copyright 2008 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.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
+import java.io.Writer;
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.ServletOutputStream;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import javax.servlet.http.HttpServletResponseWrapper;
+
+import org.springframework.util.FileCopyUtils;
+import org.springframework.util.Md5HashUtils;
+
+/**
+ * Servlet 2.3/2.4 {@link javax.servlet.Filter} that generates an <code>ETag</code> value based on the content on the
+ * response. This ETag is compared to the <code>If-None-Match</code> header of the request. If these headers are equal,
+ * the resonse content is not sent, but rather a 304 "Not Modified" status.
+ * <p/>
+ * <p/>Since the ETag is based on the response content, the response (or {@link org.springframework.web.servlet.View})
+ * is still rendered. As such, this filter only saves bandwith, not performance.
+ *
+ * @author Arjen Poutsma
+ * @since 3.0
+ */
+public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
+
+	private static String HEADER_ETAG = "ETag";
+
+	private static String HEADER_IF_NONE_MATCH = "If-None-Match";
+
+	@Override
+	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
+			throws ServletException, IOException {
+		ShallowEtagResponseWrapper wrapper = new ShallowEtagResponseWrapper(response);
+		filterChain.doFilter(request, wrapper);
+
+		byte[] body = wrapper.toByteArray();
+		String responseETag = generateETagHeaderValue(body);
+		response.setHeader(HEADER_ETAG, responseETag);
+
+		String requestETag = request.getHeader(HEADER_IF_NONE_MATCH);
+		if (responseETag.equals(requestETag)) {
+			if (logger.isTraceEnabled()) {
+				logger.trace("ETag [" + responseETag + "] equal to If-None-Match, sending 304");
+			}
+			response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
+		}
+		else {
+			if (logger.isTraceEnabled()) {
+				logger.trace("ETag [" + responseETag + "] not equal to If-None-Match [" + requestETag +
+						"], sending normal response");
+			}
+			response.setContentLength(body.length);
+			FileCopyUtils.copy(body, response.getOutputStream());
+		}
+	}
+
+	/**
+	 * Generates the ETag header value from the given response body bytes array.
+	 * <p/>
+	 * <p/>Default implementation generates an MD5 hash.
+	 *
+	 * @param bytes the
+	 * @return the ETag header value
+	 * @see Md5HashUtils
+	 */
+	protected String generateETagHeaderValue(byte[] bytes) {
+		StringBuilder builder = new StringBuilder("\"0");
+		Md5HashUtils.appendHashString(bytes, builder);
+		builder.append('"');
+		return builder.toString();
+	}
+
+	/**
+	 * {@link HttpServletRequest} wrapper that buffers all content written to the {@linkplain #getOutputStream() output
+	 * stream} and {@linkplain #getWriter() writer}, and allows this content to be retrieved via a {@link #toByteArray()
+	 * byte array}.
+	 */
+	private static class ShallowEtagResponseWrapper extends HttpServletResponseWrapper {
+
+		private final ByteArrayOutputStream content = new ByteArrayOutputStream();
+
+		private final ServletOutputStream outputStream = new ResponseServletOutputStream();
+
+		private PrintWriter writer;
+
+		private ShallowEtagResponseWrapper(HttpServletResponse response) {
+			super(response);
+		}
+
+		@Override
+		public ServletOutputStream getOutputStream() throws IOException {
+			return outputStream;
+		}
+
+		@Override
+		public PrintWriter getWriter() throws IOException {
+			if (writer == null) {
+				String characterEncoding = getCharacterEncoding();
+				Writer targetWriter = (characterEncoding != null ?
+						new OutputStreamWriter(outputStream, characterEncoding) : new OutputStreamWriter(outputStream));
+				writer = new PrintWriter(targetWriter);
+			}
+			return writer;
+		}
+
+		@Override
+		public void resetBuffer() {
+			content.reset();
+		}
+
+		@Override
+		public void reset() {
+			super.reset();
+			resetBuffer();
+		}
+
+		private byte[] toByteArray() {
+			return content.toByteArray();
+		}
+
+		private class ResponseServletOutputStream extends ServletOutputStream {
+
+			@Override
+			public void write(int b) throws IOException {
+				content.write(b);
+			}
+
+		}
+	}
+
+}