Add prefix support for environment variables

Include a filter in ConfigurationPropertiesBindingPostProcessor
that checks if the property "spring.property.prefix" exists (not blank)
and filter the system properties ensuring that the properties with
the prefix are available on property binding.

Fixes #3450

Author: lucassaldanha

spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -155,6 +155,8 @@ public class SpringApplication {
 
 	private static final String SYSTEM_PROPERTY_JAVA_AWT_HEADLESS = "java.awt.headless";
 
+	public static final String PROPERTY_BINDING_PREFIX_PROPERTY = "spring.property.prefix";
+
 	private static final Banner DEFAULT_BANNER = new SpringBootBanner();
 
 	private final Log log = LogFactory.getLog(getClass());
@@ -842,6 +844,17 @@ public void setEnvironment(ConfigurableEnvironment environment) {
 		this.environment = environment;
 	}
 
+	/**
+	 +	 * Sets the environment variables prefix that will be used to filter those variables
+	 +	 * for this application.
+	 +	 * @param environmentPrefix the prefix
+	 +	 */
+	public void setEnvironmentPrefix(String environmentPrefix) {
+		if(environmentPrefix != null && !"".equals(environmentPrefix)) {
+			System.setProperty(PROPERTY_BINDING_PREFIX_PROPERTY, environmentPrefix);
+		}
+	}
+
 	/**
 	 * Returns a mutable set of the sources that will be added to an ApplicationContext
 	 * when {@link #run(String...)} is called.

spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBindingPostProcessor.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.context.properties;
 
 import java.io.IOException;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
 
@@ -29,6 +30,7 @@
 import org.springframework.beans.factory.ListableBeanFactory;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.boot.SpringApplication;
 import org.springframework.boot.bind.PropertiesConfigurationFactory;
 import org.springframework.boot.env.PropertySourcesLoader;
 import org.springframework.context.ApplicationContext;
@@ -49,6 +51,7 @@
 import org.springframework.core.env.PropertySource;
 import org.springframework.core.env.PropertySources;
 import org.springframework.core.env.StandardEnvironment;
+import org.springframework.core.env.SystemEnvironmentPropertySource;
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
@@ -203,6 +206,13 @@ public void destroy() throws Exception {
 	}
 
 	private PropertySources deducePropertySources() {
+		String prefix = this.environment
+				.getProperty(SpringApplication.PROPERTY_BINDING_PREFIX_PROPERTY, "");
+		if (prefix != null && !"".equals(prefix)) {
+			filterSystemEnvironmentPropertySourceByPrefix(
+					(ConfigurableEnvironment) this.environment, prefix);
+		}
+
 		PropertySourcesPlaceholderConfigurer configurer = getSinglePropertySourcesPlaceholderConfigurer();
 		if (configurer != null) {
 			// Flatten the sources into a single list so they can be iterated
@@ -233,6 +243,28 @@ private PropertySourcesPlaceholderConfigurer getSinglePropertySourcesPlaceholder
 		return null;
 	}
 
+	private void filterSystemEnvironmentPropertySourceByPrefix(
+			ConfigurableEnvironment environment, String prefix) {
+		final Map<String, Object> environmentProperties = environment.getSystemProperties();
+		final Map<String, Object> filteredSystemProperties = new HashMap<String, Object>(
+				environmentProperties.size());
+
+		for (String key : environmentProperties.keySet()) {
+			if (key.startsWith(prefix)) {
+				filteredSystemProperties.put(key.substring(prefix.length()),
+						environmentProperties.get(key));
+			} else {
+				filteredSystemProperties.put(key, environmentProperties.get(key));
+			}
+		}
+
+		environment.getPropertySources()
+				.replace(StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
+						new SystemEnvironmentPropertySource(
+								StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
+								filteredSystemProperties));
+	}
+
 	private <T> T getOptionalBean(String name, Class<T> type) {
 		try {
 			return this.beanFactory.getBean(name, type);

spring-boot/src/test/java/org/springframework/boot/context/properties/EnableConfigurationPropertiesTests.java

@@ -30,6 +30,7 @@
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.SpringApplication;
 import org.springframework.boot.test.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
@@ -79,6 +80,19 @@ public void testSystemPropertiesBinding() {
 		assertEquals("foo", this.context.getBean(TestProperties.class).name);
 	}
 
+	@Test
+	public void testSystemPropertiesWithPrefixBinding() {
+		this.context.register(TestConfiguration.class);
+		System.setProperty(SpringApplication.PROPERTY_BINDING_PREFIX_PROPERTY, "bar_");
+		System.setProperty("bar_name", "foo");
+		this.context.refresh();
+		assertEquals(1, this.context.getBeanNamesForType(TestProperties.class).length);
+		assertEquals("foo", this.context.getBean(TestProperties.class).name);
+		//Assert that the environment system property still has the prefix
+		assertEquals("foo",
+				this.context.getEnvironment().getSystemProperties().get("bar_name"));
+	}
+
 	@Test
 	public void testNestedSystemPropertiesBinding() {
 		this.context.register(NestedConfiguration.class);