Fix the NPE occurred when using EnableApolloConfig with Spring 3.1.1

CHANGES.md

@@ -28,6 +28,7 @@ Apollo 2.0.0
 * [fix gray publish refresh item status](https://github.com/apolloconfig/apollo/pull/4128)
 * [Support only show difference keys when compare namespace](https://github.com/apolloconfig/apollo/pull/4165)
 * [Fix the issue that property placeholder doesn't work for dubbo reference beans](https://github.com/apolloconfig/apollo/pull/4175)
+* [Fix the NPE occurred when using EnableApolloConfig with Spring 3.1.1](https://github.com/apolloconfig/apollo/pull/4180)
 
 ------------------
 All issues and pull requests are [here](https://github.com/ctripcorp/apollo/milestone/8?closed=1)

apollo-client/src/main/java/com/ctrip/framework/apollo/spring/spi/DefaultApolloConfigRegistrarHelper.java

@@ -26,13 +26,17 @@
 import com.google.common.collect.Lists;
 import java.util.HashMap;
 import java.util.Map;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
 import org.springframework.core.annotation.AnnotationAttributes;
 import org.springframework.core.env.Environment;
 import org.springframework.core.type.AnnotationMetadata;
 
 public class DefaultApolloConfigRegistrarHelper implements ApolloConfigRegistrarHelper {
+  private static final Logger logger = LoggerFactory.getLogger(
+      DefaultApolloConfigRegistrarHelper.class);
 
   private Environment environment;
 
@@ -62,6 +66,11 @@ public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, B
   }
 
   private String[] resolveNamespaces(String[] namespaces) {
+    // no support for Spring version prior to 3.2.x, see https://github.com/apolloconfig/apollo/issues/4178
+    if (this.environment == null) {
+      logNamespacePlaceholderNotSupportedMessage(namespaces);
+      return namespaces;
+    }
     String[] resolvedNamespaces = new String[namespaces.length];
     for (int i = 0; i < namespaces.length; i++) {
       // throw IllegalArgumentException if given text is null or if any placeholders are unresolvable
@@ -70,6 +79,17 @@ private String[] resolveNamespaces(String[] namespaces) {
     return resolvedNamespaces;
   }
 
+  private void logNamespacePlaceholderNotSupportedMessage(String[] namespaces) {
+    for (String namespace : namespaces) {
+      if (namespace.contains("${")) {
+        logger.warn("Namespace placeholder {} is not supported for Spring version prior to 3.2.x,"
+                + " see https://github.com/apolloconfig/apollo/issues/4178 for more details.",
+            namespace);
+        break;
+      }
+    }
+  }
+
   @Override
   public int getOrder() {
     return Ordered.LOWEST_PRECEDENCE;