Polish "Add example of custom Actuator operations"

See gh-23028

spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -445,6 +445,13 @@ If you add a `@Bean` annotated with `@Endpoint`, any methods annotated with `@Re
 Endpoints can be exposed over HTTP using Jersey, Spring MVC, or Spring WebFlux.
 If both Jersey and Spring MVC are available, Spring MVC will be used.
 
+The following example exposes a read operation that returns a custom object:
+
+[source,java,indent=0]
+----
+include::{code-examples}/actuate/endpoint/CustomEndpointExample.java[tag=read]
+----
+
 You can also write technology-specific endpoints by using `@JmxEndpoint` or `@WebEndpoint`.
 These endpoints are restricted to their respective technologies.
 For example, `@WebEndpoint` is exposed only over HTTP and not over JMX.
@@ -475,18 +482,15 @@ Consider the following JSON request body:
 	}
 ----
 
-This can be used to invoke a write operation that takes `String name` and `int counter` parameters (name of Java parameter have to match name of JSON property).
+This can be used to invoke a write operation that takes `String name` and `int counter` parameters, as shown in the following example:
 
 [source,java,indent=0]
 ----
-    @WriteOperation
-    public void writeMethod(String name, int counter) {
-      // do the stuff
-    }
+include::{code-examples}/actuate/endpoint/CustomEndpointExample.java[tag=write]
 ----
 
 TIP: Because endpoints are technology agnostic, only simple types can be specified in the method signature.
-In particular declaring a single parameter with a custom type defining a `name` and `counter` properties is not supported.
+In particular declaring a single parameter with a `CustomData` type defining a `name` and `counter` properties is not supported.
 
 NOTE: To allow the input to be mapped to the operation method's parameters, Java code implementing an endpoint should be compiled with `-parameters`, and Kotlin code implementing an endpoint should be compiled with `-java-parameters`.
 This will happen automatically if you are using Spring Boot's Gradle plugin or if you are using Maven and `spring-boot-starter-parent`.

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/actuate/endpoint/CustomEndpointExample.java

+/*
+ * Copyright 2012-2020 the original author or authors.
+ *
+ * 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
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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 org.springframework.boot.docs.actuate.endpoint;
+
+import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
+import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
+import org.springframework.boot.actuate.endpoint.annotation.WriteOperation;
+
+/**
+ * An example of a custom actuator endpoint.
+ *
+ * @author Stephane Nicoll
+ */
+@Endpoint(id = "custom")
+public class CustomEndpointExample {
+
+	// tag::read[]
+	@ReadOperation
+	public CustomData getCustomData() {
+		return new CustomData("test", 5);
+	}
+	// end::read[]
+
+	// tag::write[]
+	@WriteOperation
+	public void updateCustomData(String name, int counter) {
+		// injects "test" and 42
+	}
+	// end::write[]
+
+	public static class CustomData {
+
+		private final String name;
+
+		private final int counter;
+
+		public CustomData(String name, int counter) {
+			this.name = name;
+			this.counter = counter;
+		}
+
+	}
+
+}