Add configuration properties validation sample

Create a new project sample that demonstrate the usage of
@ConfigurationProperties with configurationPropertiesValidator.

Fixes gh-3513

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

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2012-2015 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
+ *
+ *      http://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 sample.propertyvalidation;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.core.annotation.AnnotationUtils;
+import org.springframework.stereotype.Component;
+import org.springframework.validation.Errors;
+import org.springframework.validation.ValidationUtils;
+import org.springframework.validation.Validator;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.regex.Pattern;
+
+@Component(value = "configurationPropertiesValidator")
+public class ConfigurationPropertiesValidator implements Validator {
+
+	public static final String IP_REGEX = "^(?:[0-9]{1,3}\\.){3}[0-9]{1,3}$";
+
+	final Pattern pattern = Pattern.compile(IP_REGEX);
+
+	private Set<String> validatedClasses = new HashSet<String>() {{
+		add(SampleProperties.class.getName());
+	}};
+
+	@Override
+	public boolean supports(Class<?> aClass) {
+		return AnnotationUtils.findAnnotation(aClass, ConfigurationProperties.class) != null;
+	}
+
+	@Override
+	public void validate(Object o, Errors errors) {
+		if(validatedClasses.contains(o.getClass().getName())) {
+			doValidation(o, errors);
+		}
+	}
+
+	private void doValidation(Object o, Errors errors) {
+		ValidationUtils.rejectIfEmpty(errors, "host", "host.empty");
+		ValidationUtils.rejectIfEmpty(errors, "port", "port.empty");
+
+		SampleProperties properties = (SampleProperties) o;
+		if(!pattern.matcher(properties.getHost()).matches()) {
+			errors.rejectValue("host", "Invalid host");
+		}
+	}
+
+}

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

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2012-2015 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
+ *
+ *      http://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 sample.propertyvalidation;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.stereotype.Component;
+
+@Component
+@ConfigurationProperties
+public class SampleProperties {
+
+	private String host;
+
+	private Integer port;
+
+	public String getHost() {
+		return host;
+	}
+
+	public void setHost(String host) {
+		this.host = host;
+	}
+
+	public Integer getPort() {
+		return port;
+	}
+
+	public void setPort(Integer port) {
+		this.port = port;
+	}
+}

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

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2012-2015 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
+ *
+ *      http://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 sample.propertyvalidation;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+
+@SpringBootApplication
+@EnableConfigurationProperties
+public class SamplePropertyValidationApplication implements CommandLineRunner {
+
+	@Autowired
+	private SampleProperties properties;
+
+	@Override
+	public void run(String... args) {
+		System.out.println("host: " + this.properties.getHost());
+		System.out.println("port:" + this.properties.getPort());
+	}
+
+	public static void main(String[] args) throws Exception {
+		SpringApplication.run(SamplePropertyValidationApplication.class, args);
+	}
+
+}