Add flag spring.cloud.config.overrideNone

If true (and spring.cloud.config.allowOverride=true) then the bootstrap
property source is added *last*, so all other property sources can override
it (including local config files).

Fixes gh-26, fixes gh-27.

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/config/PropertySourceBootstrapConfiguration.java

@@ -134,15 +134,27 @@ public class PropertySourceBootstrapConfiguration implements
 		new RelaxedDataBinder(remoteProperties, "spring.cloud.config")
 				.bind(new PropertySourcesPropertyValues(incoming));
 		if (!remoteProperties.isAllowOverride()
-				|| remoteProperties.isOverrideSystemProperties()) {
+				|| (!remoteProperties.isOverrideNone() && remoteProperties
+						.isOverrideSystemProperties())) {
 			propertySources.addFirst(composite);
 			return;
 		}
+		if (remoteProperties.isOverrideNone()) {
+			propertySources.addLast(composite);
+			return;
+		}
 		if (propertySources
 				.contains(StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME)) {
-			propertySources.addAfter(
-					StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
-					composite);
+			if (!remoteProperties.isOverrideSystemProperties()) {
+				propertySources.addAfter(
+						StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
+						composite);
+			}
+			else {
+				propertySources.addBefore(
+						StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
+						composite);
+			}
 		}
 		else {
 			propertySources.addLast(composite);

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/config/PropertySourceBootstrapProperties.java

@@ -18,8 +18,23 @@ public class PropertySourceBootstrapProperties {
 	 */
 	private boolean allowOverride = true;
 
+	/**
+	 * Flag to indicate that when {@link #setAllowOverride(boolean) allowOverride} is
+	 * true, external properties should take lowest priority, and not override any
+	 * existing property sources (including local config files). Default false.
+	 */
+	private boolean overrideNone = false;
+
+	public boolean isOverrideNone() {
+		return this.overrideNone;
+	}
+
+	public void setOverrideNone(boolean overrideNone) {
+		this.overrideNone = overrideNone;
+	}
+
 	public boolean isOverrideSystemProperties() {
-		return overrideSystemProperties;
+		return this.overrideSystemProperties;
 	}
 
 	public void setOverrideSystemProperties(boolean overrideSystemProperties) {
@@ -27,7 +42,7 @@ public class PropertySourceBootstrapProperties {
 	}
 
 	public boolean isAllowOverride() {
-		return allowOverride;
+		return this.allowOverride;
 	}
 
 	public void setAllowOverride(boolean allowOverride) {

spring-cloud-context/src/test/java/org/springframework/cloud/bootstrap/config/BootstrapConfigurationTests.java

@@ -156,6 +156,32 @@ public class BootstrapConfigurationTests {
 		assertEquals("bar", this.context.getEnvironment().getProperty("bootstrap.foo"));
 	}
 
+	@Test
+	public void systemPropertyOverrideFalseWhenOverrideAllowed() {
+		PropertySourceConfiguration.MAP.put("bootstrap.foo", "bar");
+		PropertySourceConfiguration.MAP.put(
+				"spring.cloud.config.overrideSystemProperties", "false");
+		PropertySourceConfiguration.MAP.put("spring.cloud.config.allowOverride", "true");
+		System.setProperty("bootstrap.foo", "system");
+		this.context = new SpringApplicationBuilder().web(false)
+				.sources(BareConfiguration.class).run();
+		assertEquals("system", this.context.getEnvironment().getProperty("bootstrap.foo"));
+	}
+
+	@Test
+	public void overrideAllWhenOverrideAllowed() {
+		PropertySourceConfiguration.MAP.put("bootstrap.foo", "bar");
+		PropertySourceConfiguration.MAP.put("spring.cloud.config.overrideNone", "true");
+		PropertySourceConfiguration.MAP.put("spring.cloud.config.allowOverride", "true");
+		ConfigurableEnvironment environment = new StandardEnvironment();
+		environment.getPropertySources().addLast(
+				new MapPropertySource("last", Collections.<String, Object> singletonMap(
+						"bootstrap.foo", "splat")));
+		this.context = new SpringApplicationBuilder().web(false).environment(environment)
+				.sources(BareConfiguration.class).run();
+		assertEquals("splat", this.context.getEnvironment().getProperty("bootstrap.foo"));
+	}
+
 	@Test
 	public void applicationNameInBootstrapAndMain() {
 		System.setProperty("expected.name", "main");