[BAEL-5261] Customizing Zuul Exceptions (#11736)

* [BAEL-5261] Customizing Zuul Exceptions

* [BAEL-5261] Customizing Zuul Exceptions

* [BAEL-5261] Code sanitizing

spring-cloud/spring-cloud-zuul/spring-zuul-ui/src/main/java/com/baeldung/spring/cloud/zuul/filter/CustomZuulErrorApplication.java

@@ -0,0 +1,15 @@
+package com.baeldung.spring.cloud.zuul.filter;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
+import org.springframework.cloud.netflix.zuul.EnableZuulProxy;
+
+@EnableZuulProxy
+@SpringBootApplication
+public class CustomZuulErrorApplication extends SpringBootServletInitializer {
+
+    public static void main(String[] args) {
+        SpringApplication.run(CustomZuulErrorApplication.class, args);
+    }
+}

spring-cloud/spring-cloud-zuul/spring-zuul-ui/src/main/java/com/baeldung/spring/cloud/zuul/filter/CustomZuulErrorFilter.java

@@ -0,0 +1,62 @@
+package com.baeldung.spring.cloud.zuul.filter;
+
+import java.net.ConnectException;
+import java.time.Instant;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+import com.netflix.zuul.ZuulFilter;
+import com.netflix.zuul.context.RequestContext;
+import com.netflix.zuul.exception.ZuulException;
+
+@Component
+public class CustomZuulErrorFilter extends ZuulFilter {
+
+    private static final Logger log = LoggerFactory.getLogger(CustomZuulErrorFilter.class);
+
+    private static final String RESPONSE_BODY = "{\n" + "    \"timestamp\": " + "\"" + Instant.now()
+        .toString() + "\"" + ",\n" + "    \"status\": 503,\n" + "    \"error\": \"Service Unavailable\"\n" + "}";
+
+    @Override
+    public Object run() {
+        RequestContext context = RequestContext.getCurrentContext();
+        Throwable throwable = context.getThrowable();
+
+        if (throwable instanceof ZuulException) {
+            final ZuulException zuulException = (ZuulException) throwable;
+            log.error("Zuul exception: " + zuulException.getMessage());
+
+            if (throwable.getCause().getCause().getCause() instanceof ConnectException) {
+
+                // reset throwable to prevent further error handling in follow up filters
+                context.remove("throwable");
+
+                // set custom response attributes
+                context.setResponseBody(RESPONSE_BODY);
+                context.getResponse()
+                    .setContentType("application/json");
+                context.setResponseStatusCode(503);
+            }
+
+        }
+        return null;
+    }
+
+    @Override
+    public boolean shouldFilter() {
+        return true;
+    }
+
+    @Override
+    public int filterOrder() {
+        return -1;
+    }
+
+    @Override
+    public String filterType() {
+        return "error";
+    }
+
+}

spring-cloud/spring-cloud-zuul/spring-zuul-ui/src/main/java/com/baeldung/spring/cloud/zuul/filter/ZuulConfiguration.java

@@ -0,0 +1,98 @@
+package com.baeldung.spring.cloud.zuul.filter;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.boot.web.servlet.error.ErrorController;
+import org.springframework.cglib.proxy.Callback;
+import org.springframework.cglib.proxy.CallbackFilter;
+import org.springframework.cglib.proxy.Enhancer;
+import org.springframework.cglib.proxy.MethodInterceptor;
+import org.springframework.cglib.proxy.MethodProxy;
+import org.springframework.cglib.proxy.NoOp;
+import org.springframework.cloud.netflix.zuul.filters.RouteLocator;
+import org.springframework.cloud.netflix.zuul.web.ZuulController;
+import org.springframework.cloud.netflix.zuul.web.ZuulHandlerMapping;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Fix for Zuul configuration with Spring Boot 2.5.x + Zuul - "NoSuchMethodError: ErrorController.getErrorPath()":
+ */
+@Configuration
+public class ZuulConfiguration {
+    /**
+     * The path returned by ErrorController.getErrorPath() with Spring Boot < 2.5
+     * (and no longer available on Spring Boot >= 2.5).
+     */
+    private static final String ERROR_PATH = "/error";
+    private static final String METHOD = "lookupHandler";
+
+    /**
+     * Constructs a new bean post-processor for Zuul.
+     *
+     * @param routeLocator    the route locator.
+     * @param zuulController  the Zuul controller.
+     * @param errorController the error controller.
+     * @return the new bean post-processor.
+     */
+    @Bean
+    public ZuulPostProcessor zuulPostProcessor(@Autowired RouteLocator routeLocator, @Autowired ZuulController zuulController, @Autowired(required = false) ErrorController errorController) {
+        return new ZuulPostProcessor(routeLocator, zuulController, errorController);
+    }
+
+    private enum LookupHandlerCallbackFilter implements CallbackFilter {
+        INSTANCE;
+
+        @Override
+        public int accept(Method method) {
+            if (METHOD.equals(method.getName())) {
+                return 0;
+            }
+            return 1;
+        }
+    }
+
+    private enum LookupHandlerMethodInterceptor implements MethodInterceptor {
+        INSTANCE;
+
+        @Override
+        public Object intercept(Object target, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
+            if (ERROR_PATH.equals(args[0])) {
+                // by entering this branch we avoid the ZuulHandlerMapping.lookupHandler method to trigger the
+                // NoSuchMethodError
+                return null;
+            }
+            return methodProxy.invokeSuper(target, args);
+        }
+    }
+
+    private static final class ZuulPostProcessor implements BeanPostProcessor {
+
+        private final RouteLocator routeLocator;
+        private final ZuulController zuulController;
+        private final boolean hasErrorController;
+
+        ZuulPostProcessor(RouteLocator routeLocator, ZuulController zuulController, ErrorController errorController) {
+            this.routeLocator = routeLocator;
+            this.zuulController = zuulController;
+            this.hasErrorController = (errorController != null);
+        }
+
+        @Override
+        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
+            if (hasErrorController && (bean instanceof ZuulHandlerMapping)) {
+                Enhancer enhancer = new Enhancer();
+                enhancer.setSuperclass(ZuulHandlerMapping.class);
+                enhancer.setCallbackFilter(LookupHandlerCallbackFilter.INSTANCE); // only for lookupHandler
+                enhancer.setCallbacks(new Callback[] { LookupHandlerMethodInterceptor.INSTANCE, NoOp.INSTANCE });
+                Constructor<?> ctor = ZuulHandlerMapping.class.getConstructors()[0];
+                return enhancer.create(ctor.getParameterTypes(), new Object[] { routeLocator, zuulController });
+            }
+            return bean;
+        }
+    }
+}

spring-cloud/spring-cloud-zuul/spring-zuul-ui/src/main/resources/application.yml

@@ -1,5 +1,8 @@
 zuul:
+  SendErrorFilter:
+    post:
+      disable: true
   routes:
     foos:
       path: /foos/**
-      url: http://localhost:8081/spring-zuul-foos-resource/foos
+      url: http://localhost:8081/spring-zuul-foos-resource/foos

spring-cloud/spring-cloud-zuul/spring-zuul-ui/src/test/java/com/baeldung/spring/cloud/zuul/filter/CustomZuulErrorFilterLiveTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.spring.cloud.zuul.filter;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+import io.restassured.RestAssured;
+import io.restassured.response.Response;
+
+public class CustomZuulErrorFilterLiveTest {
+
+    @Test
+    public void whenSendRequestWithoutService_thenCustomError() {
+        final Response response = RestAssured.get("http://localhost:8080/foos/1");
+        assertEquals(503, response.getStatusCode());
+    }
+
+    @Test
+    public void whenSendRequestWithoutCustomErrorFilter_thenError() {
+        final Response response = RestAssured.get("http://localhost:8080/foos/1");
+        assertEquals(500, response.getStatusCode());
+    }
+
+}