ServletLogChute

/*
 * Copyright 2005 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.velocity.tools.view.servlet;

import javax.servlet.ServletContext;
import org.apache.velocity.runtime.log.LogChute;
import org.apache.velocity.runtime.RuntimeConstants;
import org.apache.velocity.runtime.RuntimeServices;
import org.apache.velocity.util.StringUtils;

/**
 * Simple wrapper for the servlet log.  This sends Velocity log
 * messages to ServletContext.log(String).
 *
 * @author <a href="mailto:geirm@apache.org">Geir Magnusson Jr.</a>
 * @author <a href="mailto:nbubna@apache.org">Nathan Bubna</a>
 * @since VelocityTools 1.3
 * @version $Revision: 71982 $ $Date: 2004-02-18 12:11:07 -0800 (Wed, 18 Feb 2004) $
 */
public class ServletLogChute implements LogChute
{
    public static final String PREFIX = " Velocity ";
    public static final String TRACE_PREFIX = PREFIX + RuntimeConstants.TRACE_PREFIX;
    public static final String DEBUG_PREFIX = PREFIX + RuntimeConstants.DEBUG_PREFIX;
    public static final String INFO_PREFIX = PREFIX + RuntimeConstants.INFO_PREFIX;
    public static final String WARN_PREFIX = PREFIX + RuntimeConstants.WARN_PREFIX;
    public static final String ERROR_PREFIX = PREFIX + RuntimeConstants.ERROR_PREFIX;
    public static final String UNKNOWN_PREFIX = PREFIX + RuntimeConstants.UNKNOWN_PREFIX;

    protected ServletContext servletContext = null;

    private int enabled = TRACE_ID;

    /**
     * Initializes the logger.
     * <br>
     * NOTE: this class expects that the ServletContext has already
     *       been placed in the runtime's application attributes
     *       under its full class name (i.e. "javax.servlet.ServletContext").
     * 
     * @throws IllegalStateException if the ServletContext is not available
     *         in the application attributes under the appropriate key.
     */
    public void init(RuntimeServices rs) throws Exception
    {
        Object obj = rs.getApplicationAttribute(ServletContext.class.getName());
        if (obj == null)
        {
            throw new IllegalStateException("Could not retrieve ServletContext from application attributes!");
        }
        servletContext = (ServletContext)obj;

        // look for a level config property
        String level = (String)rs.getProperty("runtime.log.logsystem.servlet.level");
        if (level != null)
        {
            // and set it accordingly
            if (level.equalsIgnoreCase("debug"))
            {
                setEnabledLevel(DEBUG_ID);
            }
            else if (level.equalsIgnoreCase("info"))
            {
                setEnabledLevel(INFO_ID);
            }
            else if (level.equalsIgnoreCase("warn"))
            {
                setEnabledLevel(WARN_ID);
            }
            else if (level.equalsIgnoreCase("error"))
            {
                setEnabledLevel(ERROR_ID);
            }
        }
    }

    protected String getPrefix(int level)
    {
        switch (level)
        {
            case LogChute.WARN_ID:
                return WARN_PREFIX;
            case LogChute.INFO_ID:
                return INFO_PREFIX ;
            case LogChute.DEBUG_ID:
                return DEBUG_PREFIX;
            case LogChute.TRACE_ID:
                return TRACE_PREFIX;
            case LogChute.ERROR_ID:
                return ERROR_PREFIX;
            default:
                return UNKNOWN_PREFIX;
        }
    }

    /**
     * Logs messages to either std.out or std.err
     * depending on their severity.
     *
     * @param level severity level
     * @param message complete error message
     */
    public void log(int level, String message)
    {
        // pass it off
        log(level, message, null);
    }

    /**
     * Logs messages to the servlet log so long as the specified level
     * is equal to or greater than the level this LogChute is enabled for.
     * If a java.lang.Throwable accompanies the message, it's stack trace
     * will also be sent to the servlet log as the same level as the message.
     *
     * @param level severity level
     * @param message complete error message
     * @param t the java.lang.Throwable
     */
    public void log(int level, String message, Throwable t)
    {
        if (!isLevelEnabled(level))
        {
            return;
        }

        String prefix = getPrefix(level);
        servletContext.log(prefix + message);
        if (t != null)
        {
            servletContext.log(t.getMessage() + StringUtils.stackTrace(t));
        }
    }

    /**
     * Set the minimum level at which messages will be printed.
     */
    public void setEnabledLevel(int level)
    {
        this.enabled = level;
    }

    /**
     * Returns the current minimum level at which messages will be printed.
     */
    public int getEnabledLevel()
    {
        return this.enabled;
    }

    /**
     * This will return true if the specified level
     * is equal to or higher than the level this
     * LogChute is enabled for.
     */
    public boolean isLevelEnabled(int level)
    {
        return (level >= this.enabled);
    }

}