Make Client AutoCloseable and close() idempotent

- Make AutoClosable so it can be used in try-with-resources
- Removed null check for serverConnection since it cannot be null
- Do not shutdown serverConnection or close JAX-RS client if this client
  is already closed.

Signed-off-by: Tony Germano <[email protected]>

Author: tonygermano

server/src/com/mirth/connect/client/core/Client.java

@@ -131,7 +131,11 @@
 import com.mirth.connect.util.messagewriter.EncryptionType;
 import com.mirth.connect.util.messagewriter.MessageWriterOptions;
 
-public class Client implements UserServletInterface, ConfigurationServletInterface, ChannelServletInterface, ChannelGroupServletInterface, ChannelStatusServletInterface, ChannelStatisticsServletInterface, EngineServletInterface, MessageServletInterface, EventServletInterface, AlertServletInterface, CodeTemplateServletInterface, DatabaseTaskServletInterface, UsageServletInterface, ExtensionServletInterface {
+public class Client implements UserServletInterface, ConfigurationServletInterface, ChannelServletInterface,
+        ChannelGroupServletInterface, ChannelStatusServletInterface, ChannelStatisticsServletInterface,
+        EngineServletInterface, MessageServletInterface, EventServletInterface, AlertServletInterface,
+        CodeTemplateServletInterface, DatabaseTaskServletInterface, UsageServletInterface, ExtensionServletInterface,
+        AutoCloseable {
 
     public static final int MAX_QUERY_PARAM_COLLECTION_SIZE = 100;
 
@@ -312,9 +316,9 @@ public void setRecorder(InvocationHandlerRecorder recorder) {
         this.recorder = recorder;
     }
 
+    @Override
     public void close() {
-        closed.set(true);
-        if (serverConnection != null) {
+        if (!closed.getAndSet(true)) {
             serverConnection.shutdown();
             client.close();
         }
@@ -2675,4 +2679,4 @@ public void setPluginProperties(String extensionName, Properties properties, boo
     public String getProperty(String group, String name) throws ClientException {
         return getServlet(ConfigurationServletInterface.class).getProperty(group, name);
     }
-}
+}