add feature decscription in readme (Azure#13851)

Author: yiliuTo

sdk/spring/azure-spring-boot-starter-keyvault-secrets/README.md

@@ -30,7 +30,26 @@ From a developer's perspective, Key Vault APIs accept and return secret values a
 
 For highly sensitive data, clients should consider additional layers of protection for data. Encrypting data using a separate protection key prior to storage in Key Vault is one example.
 
-Key Vault also supports a contentType field for secrets. Clients may specify the content type of a secret to assist in interpreting the secret data when it's retrieved. The maximum length of this field is 255 characters. There are no pre-defined values. The suggested usage is as a hint for interpreting the secret data. For instance, an implementation may store both passwords and certificates as secrets, then use this field to differentiate. There are no predefined values.
+Key Vault also supports a contentType field for secrets. Clients may specify the content type of a secret to assist in interpreting the secret data when it's retrieved. The maximum length of this field is 255 characters. There are no pre-defined values. The suggested usage is as a hint for interpreting the secret data.
+
+Besides, this starter provides features of supporting multiple Key Vaults, case sensitive mode of Key Vault names and using placeholder presenting Key Vault names in property file
+### Multiple Key Vault support
+
+If you want to use multiple Key Vaults you need to define names for each of the
+Key Vaults you want to use and in which order the Key Vaults should be consulted.
+If a property exists in multiple Key Vaults the order determine which value you
+will get back.
+
+### Case sensitive key mode
+
+The new case sensitive mode allows you to use case sensitive Key Vault names. Note
+that the Key Vault secret key still needs to honor the naming limitation as 
+described in the “keyvault-name” element of [About keys, secrets, and certificates](https://docs.microsoft.com/en-us/azure/key-vault/general/about-keys-secrets-certificates).
+
+If your Spring property is using a name that does not honor the Key Vault secret
+key limitation use the following technique as described by 
+[Externalized Configuration](https://docs.spring.io/autorepo/docs/spring-boot/current/reference/html/spring-boot-features.html#boot-features-external-config-placeholders-in-properties) 
+in the Spring Boot documentation.
 
 ## Examples
 ### Custom settings
@@ -111,6 +130,40 @@ public class KeyVaultSample implements CommandLineRunner {
 }
 ```
 
+### Multiple Key Vault support
+The example below shows a setup for 2 key vaults, named `keyvault1` and
+`keyvault2`. The order specifies that `keyvault1` will be consulted first.
+
+```
+azure.keyvault.order=keyvault1,keyvault2
+azure.keyvault.keyvault1.uri=put-a-azure-keyvault-uri-here
+azure.keyvault.keyvault1.client-id=put-a-azure-client-id-here
+azure.keyvault.keyvault1.client-key=put-a-azure-client-key-here
+azure.keyvault.keyvault1.tenant-id=put-a-azure-tenant-id-here
+azure.keyvault.keyvault2.uri=put-a-azure-keyvault-uri-here
+azure.keyvault.keyvault2.client-id=put-a-azure-client-id-here
+azure.keyvault.keyvault2.client-key=put-a-azure-client-key-here
+azure.keyvault.keyvault2.tenant-id=put-a-azure-tenant-id-here
+```
+Note if you decide to use multiple key vault support and you already have an
+existing configuration, please make sure you migrate that configuration to the
+multiple key vault variant. Mixing multiple key vaults with an existing single
+key vault configuration is a non supported scenario.
+
+### Case sensitive key mode
+To enable case sensitive mode, you can set the following property in the `appliation.properties`:
+```
+azure.keyvault.case-sensitive-keys=true
+```
+If your Spring property is using a name that does not honor the Key Vault secret key limitation use placeholders in properties. An example of using a placeholder:
+```
+my.not.compliant.property=${myCompliantKeyVaultSecret}
+```
+
+The application will take care of getting the value that is backed by the 
+`myCompliantKeyVaultSecret` key name and assign its value to the non compliant
+`my.not.compliant.property`.
+
 ## Troubleshooting
 ### Enable client logging
 Azure SDKs for Java offer a consistent logging story to help aid in troubleshooting application errors and expedite their resolution. The logs produced will capture the flow of an application before reaching the terminal state to help locate the root issue. View the [logging][logging] wiki for guidance about enabling logging.

sdk/spring/azure-spring-boot-starter-servicebus-jms/README.md

@@ -142,11 +142,11 @@ public class SendController {
 
         private static final String QUEUE_NAME = "<ServiceBusQueueName>";
 
-        private final Logger LOGGER = LoggerFactory.getLogger(QueueReceiveController.class);
+        private final Logger logger = LoggerFactory.getLogger(QueueReceiveController.class);
 
         @JmsListener(destination = QUEUE_NAME, containerFactory = "jmsListenerContainerFactory")
         public void receiveMessage(User user) {
-            LOGGER.info("Received message: {}", user.getName());
+            logger.info("Received message: {}", user.getName());
         }
     }
     ```
@@ -172,12 +172,12 @@ public class SendController {
 
         private static final String SUBSCRIPTION_NAME = "<ServiceBusSubscriptionName>";
 
-        private final Logger LOGGER = LoggerFactory.getLogger(TopicReceiveController.class);
+        private final Logger logger = LoggerFactory.getLogger(TopicReceiveController.class);
 
         @JmsListener(destination = TOPIC_NAME, containerFactory = "topicJmsListenerContainerFactory",
             subscription = SUBSCRIPTION_NAME)
         public void receiveMessage(User user) {
-            LOGGER.info("Received message: {}", user.getName());
+            logger.info("Received message: {}", user.getName());
         }
     }
     ```

sdk/spring/azure-spring-boot/src/samples/java/com/azure/spring/jms/QueueReceiveController.java

@@ -18,10 +18,10 @@ public class QueueReceiveController {
 
     private static final String QUEUE_NAME = "<ServiceBusQueueName>";
 
-    private final Logger LOGGER = LoggerFactory.getLogger(QueueReceiveController.class);
+    private final Logger logger = LoggerFactory.getLogger(QueueReceiveController.class);
 
     @JmsListener(destination = QUEUE_NAME, containerFactory = "jmsListenerContainerFactory")
     public void receiveMessage(User user) {
-        LOGGER.info("Received message: {}", user.getName());
+        logger.info("Received message: {}", user.getName());
     }
 }

sdk/spring/azure-spring-boot/src/samples/java/com/azure/spring/jms/TopicReceiveController.java

@@ -20,11 +20,11 @@ public class TopicReceiveController {
 
     private static final String SUBSCRIPTION_NAME = "<ServiceBusSubscriptionName>";
 
-    private final Logger LOGGER = LoggerFactory.getLogger(TopicReceiveController.class);
+    private final Logger logger = LoggerFactory.getLogger(TopicReceiveController.class);
 
     @JmsListener(destination = TOPIC_NAME, containerFactory = "topicJmsListenerContainerFactory",
         subscription = SUBSCRIPTION_NAME)
     public void receiveMessage(User user) {
-        LOGGER.info("Received message: {}", user.getName());
+        logger.info("Received message: {}", user.getName());
     }
 }