Add support for excluding some URLs in Web Servlet CommonFilter (#914)

sentinel-adapter/sentinel-web-servlet/README.md

@@ -51,6 +51,8 @@ block handler (the `UrlBlockHandler` interface) and register to `WebCallbackMana
 The `UrlCleaner` interface is designed for clean and unify the URL resource.
 For REST APIs, you have to clean the URL resource (e.g. `/foo/1` and `/foo/2` -> `/foo/:id`), or
 the amount of context and resources will exceed the threshold.
+The `UrlCleaner` interface can also exclude unused URLs(e.g. `/exclude/1` -> `/exclude/:id` -> `""`).
+The URLs will be filtered and not be resource in this way.
 
 `RequestOriginParser` interface is useful for extracting request origin (e.g. IP or appName from HTTP Header)
 from HTTP request. You can implement your own `RequestOriginParser` and register to `WebCallbackManager`.

sentinel-adapter/sentinel-web-servlet/src/main/java/com/alibaba/csp/sentinel/adapter/servlet/CommonFilter.java

@@ -73,19 +73,19 @@ public void doFilter(ServletRequest request, ServletResponse response, FilterCha
                 target = urlCleaner.clean(target);
             }
 
-            // Parse the request origin using registered origin parser.
-            String origin = parseOrigin(sRequest);
-
-            ContextUtil.enter(target, origin);
-            entry = SphU.entry(target, EntryType.IN);
-
-
-            // Add method specification if necessary
-            if (httpMethodSpecify) {
-                methodEntry = SphU.entry(sRequest.getMethod().toUpperCase() + COLON + target,
-                        EntryType.IN);
+            // If you intend to exclude some URLs, you can convert the URLs to the empty string ""
+            // in the UrlCleaner implementation.
+            if (!StringUtil.isEmpty(target)) {
+                // Parse the request origin using registered origin parser.
+                String origin = parseOrigin(sRequest);
+                ContextUtil.enter(target, origin);
+                entry = SphU.entry(target, EntryType.IN);
+                // Add method specification if necessary
+                if (httpMethodSpecify) {
+                    methodEntry = SphU.entry(sRequest.getMethod().toUpperCase() + COLON + target,
+                            EntryType.IN);
+                }
             }
-
             chain.doFilter(request, response);
         } catch (BlockException e) {
             HttpServletResponse sResponse = (HttpServletResponse) response;

sentinel-adapter/sentinel-web-servlet/src/test/java/com/alibaba/csp/sentinel/adapter/servlet/CommonFilterTest.java

@@ -89,7 +89,7 @@ public void testCommonFilterMiscellaneous() throws Exception {
 
         // Test for url cleaner.
         testUrlCleaner();
-
+        testUrlExclusion();
         testCustomOriginParser();
     }
 
@@ -139,6 +139,25 @@ public String clean(String originUrl) {
         WebCallbackManager.setUrlCleaner(new DefaultUrlCleaner());
     }
 
+    private void testUrlExclusion() throws Exception {
+        final String excludePrefix = "/exclude/";
+        String url = excludePrefix + 1;
+        WebCallbackManager.setUrlCleaner(new UrlCleaner() {
+            @Override
+            public String clean(String originUrl) {
+                if(originUrl.startsWith(excludePrefix)) {
+                    return "";
+                }
+                return originUrl;
+            }
+        });
+        this.mvc.perform(get(url).accept(MediaType.TEXT_PLAIN))
+                .andExpect(status().isOk())
+                .andExpect(content().string("Exclude 1"));
+        assertNull(ClusterBuilderSlot.getClusterNode(url));
+        WebCallbackManager.setUrlCleaner(new DefaultUrlCleaner());
+    }
+
     private void testCustomOriginParser() throws Exception {
         String url = "/hello";
         String limitOrigin = "userA";

sentinel-adapter/sentinel-web-servlet/src/test/java/com/alibaba/csp/sentinel/adapter/servlet/TestController.java

@@ -39,4 +39,9 @@ public String apiError() {
     public String apiFoo(@PathVariable("id") Long id) {
         return "Hello " + id;
     }
+
+    @GetMapping("/exclude/{id}")
+    public String apiExclude(@PathVariable("id") Long id) {
+        return "Exclude " + id;
+    }
 }