Simplify property validation sample and document need for static bean method

Closes gh-6627

Author: wilkinsona

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -1070,9 +1070,13 @@ as `@Valid` to trigger its validation. For example, building upon the above
 ----
 
 You can also add a custom Spring `Validator` by creating a bean definition called
-`configurationPropertiesValidator`. There is a
-{github-code}/spring-boot-samples/spring-boot-sample-property-validation[Validation sample]
-so you can see how to set things up.
+`configurationPropertiesValidator`. The `@Bean` method should be declared `static`. The
+configuration properties validator is created very early in the application's lifecycle
+and declaring the `@Bean` method as static allows the bean to be created without having to
+instantiate the `@Configuration` class. This avoids any problems that may be caused by
+early instantiation. There is a
+{github-code}/spring-boot-samples/spring-boot-sample-property-validation[property
+validation sample] so you can see how to set things up.
 
 TIP: The `spring-boot-actuator` module includes an endpoint that exposes all
 `@ConfigurationProperties` beans. Simply point your web browser to `/configprops`

spring-boot-samples/spring-boot-sample-property-validation/src/main/java/sample/propertyvalidation/SamplePropertyValidationApplication.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -16,42 +16,36 @@
 
 package sample.propertyvalidation;
 
-import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.CommandLineRunner;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.builder.SpringApplicationBuilder;
 import org.springframework.context.annotation.Bean;
-import org.springframework.context.annotation.Profile;
-import org.springframework.stereotype.Service;
 import org.springframework.validation.Validator;
 
 @SpringBootApplication
-public class SamplePropertyValidationApplication {
+public class SamplePropertyValidationApplication implements CommandLineRunner {
+
+	private final SampleProperties properties;
+
+	public SamplePropertyValidationApplication(SampleProperties properties) {
+		this.properties = properties;
+	}
 
 	@Bean
-	public Validator configurationPropertiesValidator() {
+	public static Validator configurationPropertiesValidator() {
 		return new SamplePropertiesValidator();
 	}
 
-	@Service
-	@Profile("app")
-	static class Startup implements CommandLineRunner {
-
-		@Autowired
-		private SampleProperties properties;
-
-		@Override
-		public void run(String... args) {
-			System.out.println("=========================================");
-			System.out.println("Sample host: " + this.properties.getHost());
-			System.out.println("Sample port: " + this.properties.getPort());
-			System.out.println("=========================================");
-		}
+	@Override
+	public void run(String... args) {
+		System.out.println("=========================================");
+		System.out.println("Sample host: " + this.properties.getHost());
+		System.out.println("Sample port: " + this.properties.getPort());
+		System.out.println("=========================================");
 	}
 
 	public static void main(String[] args) throws Exception {
-		new SpringApplicationBuilder(SamplePropertyValidationApplication.class)
-				.profiles("app").run(args);
+		new SpringApplicationBuilder(SamplePropertyValidationApplication.class).run(args);
 	}
 
 }