juneau-rest/juneau-rest-server/src/main/java/org/apache/juneau/rest/RestLogger.java

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package org.apache.juneau.rest;

import java.text.*;
import java.util.logging.*;

import javax.servlet.http.*;

import org.apache.juneau.json.*;

/**
 * Logging utility class.
 *
 * <h5 class='section'>See Also:</h5>
 * <ul>
 * 	<li class='jf'>{@link RestContext#REST_logger}
 * 	<li class='link'>{@doc juneau-rest-server.LoggingAndErrorHandling}
 * </ul>
 */
public interface RestLogger {

	/**
	 * Represents no RestLogger.
	 *
	 * <p>
	 * Used on annotation to indicate that the value should be inherited from the parent class, and
	 * ultimately {@link BasicRestLogger} if not specified at any level.
	 */
	public interface Null extends RestLogger {}

	/**
	 * Sets the logging level for this logger.
	 *
	 * @param level The new level.
	 */
	public void setLevel(Level level);

	/**
	 * Log a message to the logger.
	 *
	 * @param level The log level.
	 * @param cause The cause.
	 * @param msg The message to log.
	 * @param args Optional {@link MessageFormat}-style arguments.
	 */
	public void log(Level level, Throwable cause, String msg, Object...args);

	/**
	 * Log a message.
	 *
	 * @param level The log level.
	 * @param msg The message to log.
	 * @param args Optional {@link MessageFormat}-style arguments.
	 */
	public void log(Level level, String msg, Object...args);

	/**
	 * Same as {@link #log(Level, String, Object...)} excepts runs the arguments through {@link SimpleJsonSerializer#DEFAULT_READABLE}.
	 *
	 * <p>
	 * Serialization of arguments do not occur if message is not logged, so it's safe to use this method from within
	 * debug log statements.
	 *
	 * <h5 class='section'>Example:</h5>
	 * <p class='bcode w800'>
	 * 	logObjects(<jsf>DEBUG</jsf>, <js>"Pojo contents:\n{0}"</js>, myPojo);
	 * </p>
	 *
	 * @param level The log level.
	 * @param msg The message to log.
	 * @param args Optional {@link MessageFormat}-style arguments.
	 */
	public void logObjects(Level level, String msg, Object...args);

	/**
	 * Callback method for logging errors during HTTP requests.
	 *
	 * <p>
	 * Typically, subclasses will override this method and log errors themselves.
	 *
	 * <p>
	 * The default implementation simply logs errors to the <c>RestServlet</c> logger.
	 *
	 * <p>
	 * Here's a typical implementation showing how stack trace hashing can be used to reduce log file sizes...
	 * <p class='bcode w800'>
	 * 	<jk>protected void</jk> onError(HttpServletRequest req, HttpServletResponse res, RestException e, <jk>boolean</jk> noTrace) {
	 * 		String qs = req.getQueryString();
	 * 		String msg = <js>"HTTP "</js> + req.getMethod() + <js>" "</js> + e.getStatus() + <js>" "</js> + req.getRequestURI() + (qs == <jk>null</jk> ? <js>""</js> : <js>"?"</js> + qs);
	 * 		<jk>int</jk> c = e.getOccurrence();
	 *
	 * 		<jc>// REST_useStackTraceHashes is disabled, so we have to log the exception every time.</jc>
	 * 		<jk>if</jk> (c == 0)
	 * 			myLogger.log(Level.<jsf>WARNING</jsf>, <jsm>format</jsm>(<js>"[%s] %s"</js>, e.getStatus(), msg), e);
	 *
	 * 		<jc>// This is the first time we've countered this error, so log a stack trace
	 * 		// unless ?noTrace was passed in as a URL parameter.</jc>
	 * 		<jk>else if</jk> (c == 1 &amp;&amp; ! noTrace)
	 * 			myLogger.log(Level.<jsf>WARNING</jsf>, <jsm>format</jsm>(<js>"[%h.%s.%s] %s"</js>, e.hashCode(), e.getStatus(), c, msg), e);
	 *
	 * 		<jc>// This error occurred before.
	 * 		// Only log the message, not the stack trace.</jc>
	 * 		<jk>else</jk>
	 * 			myLogger.log(Level.<jsf>WARNING</jsf>, <jsm>format</jsm>(<js>"[%h.%s.%s] %s, %s"</js>, e.hashCode(), e.getStatus(), c, msg, e.getLocalizedMessage()));
	 * 	}
	 * </p>
	 *
	 * @param req The servlet request object.
	 * @param res The servlet response object.
	 * @param e Exception indicating what error occurred.
	 */
	public void onError(HttpServletRequest req, HttpServletResponse res, RestException e);

	/**
	 * Called at the end of a servlet request to log the request.
	 *
	 * @param req The servlet request.
	 * @param res The servlet response.
	 */
	public void log(HttpServletRequest req, HttpServletResponse res);
}