Recipe 14.3 Using a Logger Without a Configuration File


Problem

You want to use a logger in a servlet without setting up your own configuration file.

Solution

Create the logger in the servlet and use the org.apache.log4j.BasicConfigurator class to configure the logger.

Discussion

log4j allows the configuration of a logger without a provided configuration or properties file. Example 14-3 is a servlet that instantiates a logger in its init( ) method, which the servlet container calls when the servlet instance is created. The static BasicConfigurator.configure( ) method creates a ConsoleAppender ; in other words, the logger will log its messages to the console using a default format.

Example 14-3. A servlet uses BasicConfigurator to configure a logger
 package com.jspservletcookbook;  import org.apache.log4j.Logger; import org.apache.log4j.BasicConfigurator;  import javax.servlet.*; import javax.servlet.http.*;  public class LoggerNconfig extends HttpServlet { private Logger log = null;   public void init( ){          //use the root logger       log = Logger.getRootLogger( );              //this logger will log to the console with a default message format       BasicConfigurator.configure( );      }  public void doGet(HttpServletRequest request,      HttpServletResponse response)       throws ServletException, java.io.IOException {  //display a DEBUG level message         log.debug("Sending a DEBUG message");         // display an INFO level message         log.info("Sending an INFO message");  //better display some HTML         response.setContentType("text/html");         java.io.PrintWriter out = response.getWriter( );         out.println(           "<html><head><title>Servlet logging</title></head><body>");         out.println("<h2>Hello from a Logger with no Config file</h2>");         //This logger's parent is the root logger  out.println(             "Your logger name is: " + log.getName( )+"<br>");         out.println(           "Your logger parent is: " + log.getParent( ).getName( )+"<br>");  out.println("</body></html>");    } //doGet         public void doPost(HttpServletRequest request,        HttpServletResponse response) throws ServletException,         java.io.IOException {                  doGet(request,response);     }  } 

Example 14-4 shows an example message from the servlet. The message is based on a default format that includes the thread name (Thread-5), the level name ( DEBUG ), the logger name ( com.jspservletcookbook.LoggerNconfig ), and the actual message ("Sending a DEBUG message"). Recipe 14.5 shows how to create a format pattern for logging messages, so that you can customize the type of information that the logger sends.

Example 14-4. Example of a logged message using BasicConfigurator
 4061660 [Thread-5] DEBUG com.jspservletcookbook.LoggerNconfig  - Sending a DEBUG message 4061660 [Thread-5] INFO com.jspservletcookbook.LoggerNconfig  - Sending an INFO message 

Here is the pattern used for the layout associated with BasicConfigurator :

 %-4r [%t] %-5p %c %x - %m%n 

See Recipe 14.5 for details on the org.apache.log4j.PatternLayout class.

See Also

Recipe 14.2 on downloading and setting up log4j ; Recipe 14.4-Recipe 14.8 on using log4j to design your own custom logging mechanism; the log4j download site: http://jakarta.apache.org/log4j/docs/download.html; the log4j Javadoc page: http://jakarta.apache.org/log4j/docs/api/index.html; the log4j project documentation page: http://jakarta.apache.org/log4j/docs/documentation.html.



Java Servlet & JSP Cookbook
Java Servlet & JSP Cookbook
ISBN: 0596005725
EAN: 2147483647
Year: 2004
Pages: 326

Similar book on Amazon

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net