Update logging.md (#1766)

Some out-of-date documentation that didn't get updated when we upgraded to using log4j2 a while back

logging.md

@@ -2,54 +2,74 @@
 
 The Azure IoT SDK uses the [SLF4j](http://www.slf4j.org/faq.html) logging facade. In order to capture the SDK's logs, 
 you will need to provide a consumer for this logging facade. As an example, the sample projects in this repo use
-the library org.slf4j.slf4j-log4j12
-
-        <dependency>
-            <groupId>org.slf4j</groupId>
-            <artifactId>slf4j-log4j12</artifactId>
-            <version>1.7.29</version>
-        </dependency>
-
-Alongside the above dependency, you need to add log4j2.properties files into your code's resources folder that
-specify what package's logs will be captured, and at what log level. An example log4j.properties
-file can be seen in a device client sample [here](device/iot-device-samples/send-event/src/main/resources/log4j2.properties)
+the library org.apache.logging.log4j.log4j-slf4j-impl
+
+```xml
+<dependency>
+    <groupId>org.apache.logging.log4j</groupId>
+    <artifactId>log4j-api</artifactId>
+</dependency>
+<dependency>
+    <groupId>org.apache.logging.log4j</groupId>
+    <artifactId>log4j-core</artifactId>
+</dependency>
+<dependency>
+    <groupId>org.apache.logging.log4j</groupId>
+    <artifactId>log4j-slf4j-impl</artifactId>
+</dependency>
+```
+
+Alongside the above dependencies, you need to add log4j2.properties files into your code's resources folder that
+specify what package's logs will be captured, and at what log level. An example log4j2.properties
+file can be seen in a device client sample [here](iothub/device/iot-device-samples/send-event/src/main/resources/log4j2.properties)
 
 Note that the log4j2.properties file requires you to explicitly choose which packages to collect logs from. Packages to collect
 logs from must be specified in the properties file. Specified packages will include the logs
 of any subpackages, but do not include the logs of their dependencies. As an example, adding the package 
 ```com.microsoft.azure.sdk.iot.service``` will collect logs from classes like ```com.microsoft.azure.sdk.iot.service.messaging.MessagingClient```, 
 and will collect logs for classes like ```com.microsoft.azure.sdk.iot.service.transport.amqps.AmqpSendHandler``` but will not
-collect logs from a class of its dependency, such as ```com.microsoft.azure.sdk.iot.provisioning.device.transport.amqp.ErrorLoggingBaseHandler```
+collect logs from any class outside of this namespace.
 
-Adding these packages to your log4j.properties file should be sufficient to capture all logs that this SDK generates:
+Adding these packages to your log4j2.properties file should be sufficient to capture all logs that this SDK generates:
 ```
-log4j.logger.com.microsoft.azure.sdk.iot.device = DEBUG 
-log4j.logger.com.microsoft.azure.sdk.iot.service = DEBUG 
-log4j.logger.com.microsoft.azure.sdk.iot.deps = DEBUG 
-log4j.logger.com.microsoft.azure.sdk.iot.provisioning.device = DEBUG 
-log4j.logger.com.microsoft.azure.sdk.iot.provisioning.service = DEBUG 
-log4j.logger.com.microsoft.azure.sdk.iot.provisioning.security = DEBUG 
+logger.sdk.device.name = com.microsoft.azure.sdk.iot.device
+logger.sdk.device.level = INFO
+
+logger.sdk.service.name = com.microsoft.azure.sdk.iot.service
+logger.sdk.service.level = INFO
+
+logger.sdk.provisioningDevice.name = com.microsoft.azure.sdk.iot.provisioning.device
+logger.sdk.provisioningDevice.level = INFO
+
+logger.sdk.provisioningService.name = com.microsoft.azure.sdk.iot.provisioning.service
+logger.sdk.provisioningService.level = INFO
+
+logger.sdk.provisioningService.name = com.microsoft.azure.sdk.iot.provisioning.security
+logger.sdk.provisioningSecurity.level = INFO 
 ```
 
 Or for simplicity:
 ```
-log4j.logger.com.microsoft.azure.sdk.iot = DEBUG 
+logger.sdk.name = com.microsoft.azure.sdk.iot
+logger.sdk.level = INFO
 ```
 
 This SDK does print logs at TRACE, DEBUG, INFO, WARN, and ERROR levels, and your log4j.properties file
-allows you to choose these levels for each package. For example, to get trace level logs in the deps package,
-but info level logs in the device and service packages, your log4j.properties file would include
+allows you to choose these levels for each package. For example, to get trace level logs in the service client package,
+but info level logs in the device client package, your log4j.properties file would include
 
 ```
-log4j.logger.com.microsoft.azure.sdk.iot.device = INFO 
-log4j.logger.com.microsoft.azure.sdk.iot.service = INFO 
-log4j.logger.com.microsoft.azure.sdk.iot.deps = TRACE 
+logger.sdk.device.name = com.microsoft.azure.sdk.iot.device
+logger.sdk.device.level = INFO
+
+logger.sdk.service.name = com.microsoft.azure.sdk.iot.service
+logger.sdk.service.level = TRACE
 ```
 
 Another notable logging consumer that works with SLF4j is [logback](http://logback.qos.ch/). For more information on 
 using logback with SLF4j, see [this tutorial](https://mkyong.com/logging/slf4j-logback-tutorial/)
 
 You can also make your existing logging framework compatible with SLF4j as documented [here](http://www.slf4j.org/faq.html#slf4j_compatible)
 
-
+For additional details about configuring a log4j2.properties file, or to see what alternatives there are for setting these logging settings, see the official Apache documentation [here](https://logging.apache.org/log4j/2.x/manual/configuration.html).