Parameterize spring_version in the README for javadoc links

README.adoc

+:spring_version: 4.0.0.RC1
 :toc:
 :project_id: gs-rest-service
 :spring_version: 3.2.4.RELEASE
 
 == Create a resource controller
 
-In Spring's approach to building RESTful web services, HTTP requests are handled by a controller. These components are easily identified by the http://docs.spring.io/spring/docs/4.0.0.RC1/javadoc-api/org/springframework/stereotype/Controller.html[`@Controller`] annotation, and the `GreetingController` below handles `GET` requests for `/greeting` by returning a new instance of the `Greeting` class:
+In Spring's approach to building RESTful web services, HTTP requests are handled by a controller. These components are easily identified by the http://docs.spring.io/spring/docs/{spring_version}/javadoc-api/org/springframework/stereotype/Controller.html[`@Controller`] annotation, and the `GreetingController` below handles `GET` requests for `/greeting` by returning a new instance of the `Greeting` class:
 
 `src/main/java/hello/GreetingController.java`
 [source,java]
 
 A key difference between a traditional MVC controller and the RESTful web service controller above is the way that the HTTP response body is created. Rather than relying on a link:/understanding/view-templates[view technology] to perform server-side rendering of the greeting data to HTML, this RESTful web service controller simply populates and returns a `Greeting` object. The object data will be written directly to the HTTP response as JSON.
 
-To accomplish this, the http://docs.spring.io/spring/docs/4.0.0.RC1/javadoc-api/org/springframework/web/bind/annotation/ResponseBody.html[`@ResponseBody`] annotation on the `greeting()` method tells Spring MVC that it does not need to render the greeting object through a server-side view layer, but that instead that the greeting object returned _is_ the response body, and should be written out directly.
+To accomplish this, the http://docs.spring.io/spring/docs/{spring_version}/javadoc-api/org/springframework/web/bind/annotation/ResponseBody.html[`@ResponseBody`] annotation on the `greeting()` method tells Spring MVC that it does not need to render the greeting object through a server-side view layer, but that instead that the greeting object returned _is_ the response body, and should be written out directly.
 
-The `Greeting` object must be converted to JSON. Thanks to Spring's HTTP message converter support, you don't need to do this conversion manually. Because http://wiki.fasterxml.com/JacksonHome[Jackson 2] is on the classpath, Spring's http://docs.spring.io/spring/docs/4.0.0.RC1/javadoc-api/org/springframework/http/converter/json/MappingJackson2HttpMessageConverter.html[`MappingJackson2HttpMessageConverter`] is automatically chosen to convert the `Greeting` instance to JSON.
+The `Greeting` object must be converted to JSON. Thanks to Spring's HTTP message converter support, you don't need to do this conversion manually. Because http://wiki.fasterxml.com/JacksonHome[Jackson 2] is on the classpath, Spring's http://docs.spring.io/spring/docs/{spring_version}/javadoc-api/org/springframework/http/converter/json/MappingJackson2HttpMessageConverter.html[`MappingJackson2HttpMessageConverter`] is automatically chosen to convert the `Greeting` instance to JSON.
 
 
 == Make the application executable
 
 The `main()` method defers to the http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/SpringApplication.html[`SpringApplication`] helper class, providing `Application.class` as an argument to its `run()` method. This tells Spring to read the annotation metadata from `Application` and to manage it as a component in the link:/understanding/application-context[Spring application context].
 
-The `@ComponentScan` annotation tells Spring to search recursively through the `hello` package and its children for classes marked directly or indirectly with Spring's http://docs.spring.io/spring/docs/4.0.0.RC1/javadoc-api/org/springframework/stereotype/Component.html[`@Component`] annotation. This directive ensures that Spring finds and registers the `GreetingController`, because it is marked with `@Controller`, which in turn is a kind of `@Component` annotation.
+The `@ComponentScan` annotation tells Spring to search recursively through the `hello` package and its children for classes marked directly or indirectly with Spring's http://docs.spring.io/spring/docs/{spring_version}/javadoc-api/org/springframework/stereotype/Component.html[`@Component`] annotation. This directive ensures that Spring finds and registers the `GreetingController`, because it is marked with `@Controller`, which in turn is a kind of `@Component` annotation.
 
-The http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html[`@EnableAutoConfiguration`] annotation switches on reasonable default behaviors based on the content of your classpath. For example, because the application depends on the embeddable version of Tomcat (tomcat-embed-core.jar), a Tomcat server is set up and configured with reasonable defaults on your behalf. And because the application also depends on Spring MVC (spring-webmvc.jar), a Spring MVC http://docs.spring.io/spring/docs/4.0.0.RC1/javadoc-api/org/springframework/web/servlet/DispatcherServlet.html[`DispatcherServlet`] is configured and registered for you — no `web.xml` necessary! Auto-configuration is a powerful, flexible mechanism. See the http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html[API documentation] for further details.
+The http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html[`@EnableAutoConfiguration`] annotation switches on reasonable default behaviors based on the content of your classpath. For example, because the application depends on the embeddable version of Tomcat (tomcat-embed-core.jar), a Tomcat server is set up and configured with reasonable defaults on your behalf. And because the application also depends on Spring MVC (spring-webmvc.jar), a Spring MVC http://docs.spring.io/spring/docs/{spring_version}/javadoc-api/org/springframework/web/servlet/DispatcherServlet.html[`DispatcherServlet`] is configured and registered for you — no `web.xml` necessary! Auto-configuration is a powerful, flexible mechanism. See the http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html[API documentation] for further details.
 
 include::https://raw.github.com/spring-guides/getting-started-macros/master//build_an_executable_jar_subhead.adoc[]