fix #1034, to make sure ApolloBootstrapPropertySources is in the first place

apollo-client/src/main/java/com/ctrip/framework/apollo/spring/config/PropertySourcesProcessor.java

@@ -25,6 +25,8 @@ import org.springframework.core.env.Environment;
 
 import java.util.Collection;
 import java.util.Iterator;
+import org.springframework.core.env.MutablePropertySources;
+import org.springframework.core.env.PropertySource;
 
 /**
  * Apollo Property Sources processor for Spring Annotation Based Application. <br /> <br />
@@ -81,6 +83,10 @@ public class PropertySourcesProcessor implements BeanFactoryPostProcessor, Envir
     // add after the bootstrap property source or to the first
     if (environment.getPropertySources()
         .contains(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
+
+      // ensure ApolloBootstrapPropertySources is still the first
+      ensureBootstrapPropertyPrecedence(environment);
+
       environment.getPropertySources()
           .addAfter(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME, composite);
     } else {
@@ -88,6 +94,21 @@ public class PropertySourcesProcessor implements BeanFactoryPostProcessor, Envir
     }
   }
 
+  private void ensureBootstrapPropertyPrecedence(ConfigurableEnvironment environment) {
+    MutablePropertySources propertySources = environment.getPropertySources();
+
+    PropertySource<?> bootstrapPropertySource = propertySources
+        .get(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME);
+
+    // not exists or already in the first place
+    if (bootstrapPropertySource == null || propertySources.precedenceOf(bootstrapPropertySource) == 0) {
+      return;
+    }
+
+    propertySources.remove(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME);
+    propertySources.addFirst(bootstrapPropertySource);
+  }
+
   private void initializeAutoUpdatePropertiesFeature(ConfigurableListableBeanFactory beanFactory) {
     if (!configUtil.isAutoUpdateInjectedSpringPropertiesEnabled()) {
       return;