Fix Jetty metrics instrumentation

The factory is being asked to create a server before our configuration
has a chance to kick in.

Relates to #593.

micrometer-spring-legacy/src/main/java/io/micrometer/spring/autoconfigure/web/jetty/JettyMetricsConfiguration.java

@@ -16,33 +16,23 @@
 package io.micrometer.spring.autoconfigure.web.jetty;
 
 import io.micrometer.core.instrument.MeterRegistry;
-import io.micrometer.core.instrument.binder.jetty.InstrumentedQueuedThreadPool;
-import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
-import org.springframework.boot.context.embedded.jetty.JettyEmbeddedServletContainerFactory;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
-import java.util.Collections;
-
 /**
  * @author Manabu Matsuzaki
  * @author Jon Schneider
+ * @author Michael Weirauch
  */
 @Configuration
 @ConditionalOnClass(name = "org.eclipse.jetty.server.Server")
 @ConditionalOnMissingClass("org.apache.catalina.startup.Tomcat")
 public class JettyMetricsConfiguration {
-    private final MeterRegistry registry;
-
-    public JettyMetricsConfiguration(MeterRegistry registry) {
-        this.registry = registry;
-    }
 
-    @Autowired(required = false)
-    public void instrumentJettyThreadPool(JettyEmbeddedServletContainerFactory jettyContainerFactory) {
-        if (jettyContainerFactory != null) {
-            jettyContainerFactory.setThreadPool(new InstrumentedQueuedThreadPool(registry, Collections.emptyList()));
-        }
+    @Bean
+    JettyMetricsPostProcessor jettyMetricsPostProcessor(MeterRegistry registry) {
+        return new JettyMetricsPostProcessor(registry);
     }
 }

micrometer-spring-legacy/src/main/java/io/micrometer/spring/autoconfigure/web/jetty/JettyMetricsPostProcessor.java

@@ -0,0 +1,57 @@
+/**
+ * Copyright 2017 Pivotal Software, Inc.
+ * <p>
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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 io.micrometer.spring.autoconfigure.web.jetty;
+
+import java.util.Collections;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.boot.context.embedded.jetty.JettyEmbeddedServletContainerFactory;
+import org.springframework.core.Ordered;
+
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.binder.jetty.InstrumentedQueuedThreadPool;
+
+/**
+ * @author Michael Weirauch
+ */
+public class JettyMetricsPostProcessor implements BeanPostProcessor, Ordered {
+    private final MeterRegistry registry;
+
+    JettyMetricsPostProcessor(MeterRegistry registry) {
+        this.registry = registry;
+    }
+
+    @Override
+    public Object postProcessBeforeInitialization(Object bean, String beanName)
+            throws BeansException {
+        return bean;
+    }
+
+    @Override
+    public Object postProcessAfterInitialization(Object bean, String beanName) {
+        if (bean instanceof JettyEmbeddedServletContainerFactory) {
+            ((JettyEmbeddedServletContainerFactory) bean).setThreadPool(
+                    new InstrumentedQueuedThreadPool(registry, Collections.emptyList()));
+        }
+        return bean;
+    }
+
+    @Override
+    public int getOrder() {
+        return Ordered.HIGHEST_PRECEDENCE;
+    }
+}