From 6f9099ff5066e536b1fe31315be1b0245579d348 Mon Sep 17 00:00:00 2001
From: Graham McGregor <graham_mcgregor@trendmicro.com>
Date: Fri, 24 Mar 2017 13:56:16 -0400
Subject: [PATCH] Allow specificying extensions to exclude

I want to apply this filter to a subfolder (like /static/), and exclude
certain file types (like .html). Tomcat has very limited url pattern
matching available which doesn't let me do this.
---
 .../java/com/samaxes/filter/CacheFilter.java  | 29 +++++++++++++++++++
 .../filter/util/CacheConfigParameter.java     |  9 +++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/main/java/com/samaxes/filter/CacheFilter.java b/src/main/java/com/samaxes/filter/CacheFilter.java
index a7ae1be..443b63c 100644
--- a/src/main/java/com/samaxes/filter/CacheFilter.java
+++ b/src/main/java/com/samaxes/filter/CacheFilter.java
@@ -19,6 +19,11 @@
 package com.samaxes.filter;
 
 import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
 
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
@@ -26,6 +31,7 @@
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpServletResponseWrapper;
 
@@ -177,6 +183,8 @@ public class CacheFilter implements Filter {
 
     private String vary;
 
+    private List<String> excludeExtensions;
+
     /**
      * {@inheritDoc}
      */
@@ -194,6 +202,14 @@ public void init(FilterConfig filterConfig) throws ServletException {
                 : Cacheability.PUBLIC;
         mustRevalidate = Boolean.valueOf(filterConfig.getInitParameter(CacheConfigParameter.MUST_REVALIDATE.getName()));
         vary = filterConfig.getInitParameter(CacheConfigParameter.VARY.getName());
+		excludeExtensions = Arrays.stream(
+						Optional.ofNullable(
+								filterConfig.getInitParameter(CacheConfigParameter.EXCLUDE_EXTENSIONS.getName()))
+						.orElse("")
+						.split(" ")
+					)
+					.filter(ext -> !ext.isEmpty())
+					.collect(Collectors.toList());
     }
 
     /**
@@ -205,6 +221,19 @@ public void init(FilterConfig filterConfig) throws ServletException {
     @Override
     public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
             throws IOException, ServletException {
+		// If extensions provided filter on them
+		if (!excludeExtensions.isEmpty()) {
+			HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
+			String uri = httpServletRequest.getRequestURI();
+			String ext = uri.substring(uri.lastIndexOf("."));
+			// if found, continue filter chain and skip our the rest of our cache filter
+			if (excludeExtensions.contains(ext)) {
+				filterChain.doFilter(servletRequest, servletResponse);
+				return;
+			}
+		}
+
+
         HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
         StringBuilder cacheControl = new StringBuilder(cacheability.getValue()).append(", max-age=").append(expiration);
         if (mustRevalidate) {
diff --git a/src/main/java/com/samaxes/filter/util/CacheConfigParameter.java b/src/main/java/com/samaxes/filter/util/CacheConfigParameter.java
index 636ee5f..a31429d 100644
--- a/src/main/java/com/samaxes/filter/util/CacheConfigParameter.java
+++ b/src/main/java/com/samaxes/filter/util/CacheConfigParameter.java
@@ -42,7 +42,14 @@ public enum CacheConfigParameter {
      * Cache directive to instructs proxies to cache different versions of the same resource based on specific
      * request-header fields.
      */
-    VARY("vary");
+    VARY("vary"),
+    /**
+     * Cache directive to define any file extensions that should be ignored. Expect a space delimited list.
+     *
+     * Example: .html .map .xyz
+     */
+    EXCLUDE_EXTENSIONS("exclude-extensions"),
+    ;
 
     private final String name;