commit 6aa220d5fa284da01f32650cf742003da9051321
author Shawn O. Pearce <sop@google.com> Fri Feb 27 09:20:03 2009 -0800
committer Shawn O. Pearce <sop@google.com> Fri Feb 27 09:22:13 2009 -0800
tree db4fa67cd173b8e06a64b9d8605acc22c555a673
parent cf497a487a0819b5a4906454be8cf6d3555af1df

Add a reusuable servlet filter to control resource caching

This filter can be injected into an application's web.xml, automatically
setting resources to be cached for 1 year if the URL ends in ".cache.ext"
where ext is one of the common file types used by GWT.

Signed-off-by: Shawn O. Pearce <sop@google.com>

src/main/java/com/google/gwtexpui/server/CacheControlFilter.java

diff --git a/src/main/java/com/google/gwtexpui/server/CacheControlFilter.java b/src/main/java/com/google/gwtexpui/server/CacheControlFilter.java
new file mode 100644
index 0000000..dde2cac
--- /dev/null
+++ b/src/main/java/com/google/gwtexpui/server/CacheControlFilter.java
@@ -0,0 +1,108 @@
+// Copyright 2008 Google Inc.
+//
+// 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 com.google.gwtexpui.server;
+
+import java.io.IOException;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+/**
+ * Forces GWT resources to cache for a very long time.
+ * <p>
+ * GWT compiled JavaScript and ImageBundles can be cached indefinitely by a
+ * browser and/or an edge proxy, as they never contain user-specific data and
+ * are named by a unique checksum. If their content is ever modified then the
+ * URL changes, so user agents would request a different resource. We force
+ * these resources to have very long expiration times.
+ * <p>
+ * To use, add the following block to your <code>web.xml</code>:
+ * 
+ * <pre>
+ * &lt;filter&gt;
+ *     &lt;filter-name&gt;CacheControl&lt;/filter-name&gt;
+ *     &lt;filter-class&gt;com.google.gwtexpui.server.CacheControlFilter&lt;/filter-class&gt;
+ *   &lt;/filter&gt;
+ *   &lt;filter-mapping&gt;
+ *     &lt;filter-name&gt;CacheControl&lt;/filter-name&gt;
+ *     &lt;url-pattern&gt;/*&lt;/url-pattern&gt;
+ *   &lt;/filter-mapping&gt;
+ * </pre>
+ */
+public class CacheControlFilter implements Filter {
+  public void init(final FilterConfig config) {
+  }
+
+  public void destroy() {
+  }
+
+  public void doFilter(final ServletRequest sreq, final ServletResponse srsp,
+      final FilterChain chain) throws IOException, ServletException {
+    final HttpServletRequest req = (HttpServletRequest) sreq;
+    final HttpServletResponse rsp = (HttpServletResponse) srsp;
+    final String pathInfo = pathInfo(req);
+
+    if (cacheForever(pathInfo)) {
+      final long now = System.currentTimeMillis();
+      rsp.setHeader("Cache-Control", "max-age=31536000,public");
+      rsp.setDateHeader("Expires", now + 31536000000L);
+      rsp.setDateHeader("Date", now);
+
+    } else if (nocache(pathInfo)) {
+      rsp.setHeader("Expires", "Fri, 01 Jan 1980 00:00:00 GMT");
+      rsp.setHeader("Pragma", "no-cache");
+      rsp.setHeader("Cache-Control", "no-cache, must-revalidate");
+      rsp.setDateHeader("Date", System.currentTimeMillis());
+    }
+
+    chain.doFilter(req, rsp);
+  }
+
+  private static boolean cacheForever(final String pathInfo) {
+    if (pathInfo.endsWith(".cache.html")) {
+      return true;
+    } else if (pathInfo.endsWith(".cache.gif")) {
+      return true;
+    } else if (pathInfo.endsWith(".cache.png")) {
+      return true;
+    } else if (pathInfo.endsWith(".cache.css")) {
+      return true;
+    } else if (pathInfo.endsWith(".cache.jar")) {
+      return true;
+    } else if (pathInfo.endsWith(".cache.swf")) {
+      return true;
+    }
+    return false;
+  }
+
+  private static boolean nocache(final String pathInfo) {
+    if (pathInfo.endsWith(".nocache.js")) {
+      return true;
+    }
+    return false;
+  }
+
+  private static String pathInfo(final HttpServletRequest req) {
+    final String uri = req.getRequestURI();
+    final String ctx = req.getContextPath();
+    return uri.startsWith(ctx) ? uri.substring(ctx.length()) : uri;
+  }
+}