===================== Logging and Debugging ===================== There are a few logging frameworks available for use in Java. Logging is preferable to printing to stdout or stderr with ``System.out.println()`` for a number of reasons: * Logged messages are labeled with a source name, making it easier to figure out where the logged messages are coming from. * Logged messages have a severity level which allows for simple filtering (e.g. disable all non-critical notices). * The available logger frameworks allow you to enable or disable messages from certain sources. Sponge uses ``org.slf4j.Logger``, not ``java.util.logging.Logger``. Getting a Logger ================ The Guice module used during the initialization of plugins has a plugin-scoped logger. This allows you to annotate a field, method, or constructor with ``@Inject`` to get the logger for your plugin, which is pre-configured with the correct plugin ID. .. note:: See :doc:`plugin-class` for information on configuring your plugin ID. **Example - Field** .. code-block:: java import com.google.inject.Inject; import org.slf4j.Logger; @Inject private Logger logger; **Example - Method** .. code-block:: java private Logger logger; @Inject private void setLogger(Logger logger) { this.logger = logger; } **Example - Constructor** .. code-block:: java // For the purpose of this example, "Banana" is the class name private Logger logger; @Inject public Banana(Logger logger) { this.logger = logger; } It is recommended to set your logger in your main plugin class, as it is instantiated with the Guice injector when the plugin is loaded. Creating a getter method for your logger in the same class in which it was set is also ideal, although optional. An example getter method is illustrated below. .. code-block:: java public Logger getLogger() { return logger; } Emitting Messages ================= Emitting a message with your logger is very simple. .. note:: The following example assumes that the getter method for your logger is named ``getLogger()``, as shown in the previous section. This may differ for you depending on what you named your getter method. .. code-block:: java getLogger().info(String); getLogger().debug(String); getLogger().warn(String); getLogger().error(String); The String is the message you wish to emit. For example: .. code-block:: java getLogger().warn("This is a warning!");