improved jndi datasource support.

src/main/java/com/alibaba/druid/pool/DruidDataSource.java

@@ -1788,6 +1788,16 @@ public class DruidDataSource extends DruidAbstractDataSource implements DruidDat
 
     @Override
     public Connection getConnection(String username, String password) throws SQLException {
+        if (this.username == null
+                && this.password == null
+                && username != null
+                && password != null) {
+            this.username = username;
+            this.password = password;
+
+            return getConnection();
+        }
+
         if (!StringUtils.equals(username, this.username)) {
             throw new UnsupportedOperationException("Not supported by DruidDataSource");
         }