Use the unified context name instead in Web Servlet filter and code improvement (#944)

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

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

@@ -1,6 +1,7 @@
 # Sentinel Web Servlet Filter
 
-Sentinel provides Servlet filter integration to enable flow control for web requests. Add the following dependency in `pom.xml` (if you are using Maven):
+Sentinel provides Servlet filter integration to enable flow control for web requests.
+Add the following dependency in `pom.xml` (if you are using Maven):
 
 ```xml
 <dependency>
@@ -10,7 +11,7 @@ Sentinel provides Servlet filter integration to enable flow control for web requ
 </dependency>
 ```
 
-To use the filter, you can simply configure your `web.xml` with:
+To activate the filter, you can simply configure your `web.xml` with:
 
 ```xml
 <filter>
@@ -34,8 +35,9 @@ public class FilterConfig {
     public FilterRegistrationBean sentinelFilterRegistration() {
         FilterRegistrationBean<Filter> registration = new FilterRegistrationBean<>();
         registration.setFilter(new CommonFilter());
+        // Set the matching URL pattern for the filter.
         registration.addUrlPatterns("/*");
-        registration.setName("sentinelFilter");
+        registration.setName("sentinelCommonFilter");
         registration.setOrder(1);
 
         return registration;
@@ -43,7 +45,7 @@ public class FilterConfig {
 }
 ```
 
-When a request is blocked, Sentinel servlet filter will give a default page indicating the request blocked.
+When a request is blocked, Sentinel servlet filter will display a default page indicating the request is rejected.
 If customized block page is set (via `WebServletConfig.setBlockPage(blockPage)` method),
 the filter will redirect the request to provided URL. You can also implement your own
 block handler (the `UrlBlockHandler` interface) and register to `WebCallbackManager`.
@@ -51,8 +53,10 @@ 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.
+
+If you need to exclude some URLs (that should not be recorded as Sentinel resources), you could also
+leverage the `UrlCleaner` interface. You may unify the unwanted URLs to the empty string `""`,
+then the URLs will be excluded (since Sentinel 1.6.3).
 
 `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

@@ -33,6 +33,7 @@ import com.alibaba.csp.sentinel.Tracer;
 import com.alibaba.csp.sentinel.adapter.servlet.callback.RequestOriginParser;
 import com.alibaba.csp.sentinel.adapter.servlet.callback.UrlCleaner;
 import com.alibaba.csp.sentinel.adapter.servlet.callback.WebCallbackManager;
+import com.alibaba.csp.sentinel.adapter.servlet.config.WebServletConfig;
 import com.alibaba.csp.sentinel.adapter.servlet.util.FilterUtil;
 import com.alibaba.csp.sentinel.context.ContextUtil;
 import com.alibaba.csp.sentinel.slots.block.BlockException;
@@ -59,9 +60,8 @@ public class CommonFilter implements Filter {
     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
             throws IOException, ServletException {
         HttpServletRequest sRequest = (HttpServletRequest) request;
-        Entry entry = null;
-
-        Entry methodEntry = null;
+        Entry urlEntry = null;
+        Entry httpMethodUrlEntry = null;
 
         try {
             String target = FilterUtil.filterTarget(sRequest);
@@ -78,11 +78,11 @@ public class CommonFilter implements Filter {
             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);
+                ContextUtil.enter(WebServletConfig.WEB_SERVLET_CONTEXT_NAME, origin);
+                urlEntry = SphU.entry(target, EntryType.IN);
                 // Add method specification if necessary
                 if (httpMethodSpecify) {
-                    methodEntry = SphU.entry(sRequest.getMethod().toUpperCase() + COLON + target,
+                    httpMethodUrlEntry = SphU.entry(sRequest.getMethod().toUpperCase() + COLON + target,
                             EntryType.IN);
                 }
             }
@@ -91,21 +91,16 @@ public class CommonFilter implements Filter {
             HttpServletResponse sResponse = (HttpServletResponse) response;
             // Return the block page, or redirect to another URL.
             WebCallbackManager.getUrlBlockHandler().blocked(sRequest, sResponse, e);
-        } catch (IOException e2) {
-            Tracer.trace(e2);
+        } catch (IOException | ServletException | RuntimeException e2) {
+            Tracer.traceEntry(e2, urlEntry);
+            Tracer.traceEntry(e2, httpMethodUrlEntry);
             throw e2;
-        } catch (ServletException e3) {
-            Tracer.trace(e3);
-            throw e3;
-        } catch (RuntimeException e4) {
-            Tracer.trace(e4);
-            throw e4;
         } finally {
-            if (methodEntry != null) {
-                methodEntry.exit();
+            if (httpMethodUrlEntry != null) {
+                httpMethodUrlEntry.exit();
             }
-            if (entry != null) {
-                entry.exit();
+            if (urlEntry != null) {
+                urlEntry.exit();
             }
             ContextUtil.exit();
         }

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

@@ -30,6 +30,7 @@ import com.alibaba.csp.sentinel.Entry;
 import com.alibaba.csp.sentinel.SphU;
 import com.alibaba.csp.sentinel.Tracer;
 import com.alibaba.csp.sentinel.adapter.servlet.callback.WebCallbackManager;
+import com.alibaba.csp.sentinel.adapter.servlet.config.WebServletConfig;
 import com.alibaba.csp.sentinel.adapter.servlet.util.FilterUtil;
 import com.alibaba.csp.sentinel.context.ContextUtil;
 import com.alibaba.csp.sentinel.slots.block.BlockException;
@@ -52,26 +53,18 @@ public class CommonTotalFilter implements Filter {
     public void doFilter(ServletRequest request, ServletResponse response,
                          FilterChain chain) throws IOException, ServletException {
         HttpServletRequest sRequest = (HttpServletRequest)request;
-        String target = FilterUtil.filterTarget(sRequest);
-        target = WebCallbackManager.getUrlCleaner().clean(target);
 
         Entry entry = null;
         try {
-            ContextUtil.enter(target);
+            ContextUtil.enter(WebServletConfig.WEB_SERVLET_CONTEXT_NAME);
             entry = SphU.entry(TOTAL_URL_REQUEST);
             chain.doFilter(request, response);
         } catch (BlockException e) {
             HttpServletResponse sResponse = (HttpServletResponse)response;
             WebCallbackManager.getUrlBlockHandler().blocked(sRequest, sResponse, e);
-        } catch (IOException e2) {
+        } catch (IOException | ServletException | RuntimeException e2) {
             Tracer.trace(e2);
             throw e2;
-        } catch (ServletException e3) {
-            Tracer.trace(e3);
-            throw e3;
-        } catch (RuntimeException e4) {
-            Tracer.trace(e4);
-            throw e4;
         } finally {
             if (entry != null) {
                 entry.exit();

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

@@ -24,6 +24,8 @@ import com.alibaba.csp.sentinel.config.SentinelConfig;
  */
 public class WebServletConfig {
 
+    public static final String WEB_SERVLET_CONTEXT_NAME = "sentinel_web_servlet_context";
+
     public static final String BLOCK_PAGE = "csp.sentinel.web.servlet.block.page";
 
     /**