18.2 Log4j in a Web Application

Now that we have the basics of Log4J we shall move on to using it in a Java web application. The developer of the application would usually add the logging statements before it is handed to the administrator. However, it is useful to know the syntax and usage of the different options available. we'll start off by using the simple example again, but this time we'll use it from a JSP page in a web application called logging. First though, we need to configure the Logger. now we There is already the foundation of log4j, we will transfer to use it in a Java web application. We will start again through a simple example, but this time we call JSP page from the web application. First, we need to configure Logger.

Configuring a logger in a Web Application

Configuring Logger in a web application

.As we saw earlier, the easiest way to configure a Logger was to use a configuration file. When using Log4J in a web application it is a good idea to set up a Logger for the entire web application at startup. This can be achieved by Using An Initialization Servlet That Loads The Configuration File Into the Web Application. To configure the easiest way to configure Logger is to use the configuration file, when using log4j in a web application, set a logger for the entire application at startup. It is a good idea. This can be done by using a initialization servlet, which loads the configuration file to the application when started.

The Initialization Servlet

Here is the initialization servlet:

Package Wrox;

Import javax.servlet.servletException;

Import javax.servlet.http.httpservlet;

Import javax.servlet.http.httpservletRequest;

Import javax.servlet.http.httpservletResponse;

Import java.io.printwriter;

Import java.io.ioException;

Import org.apache.log4j.propertyConfigurator;

Public class log4jinitservlet extends httpservlet {

The configuration within the application range is called in the init () method. When the servlet is loaded by Tomcat, the init () method is automatically called .The Application-Wide Configuration Happens in the init () Method. Make Logger startup Once you can use:

// Initialize the servlet by loading the log4j Properties File

public void init () throws ServletException {The properties file will be stored in the $ CATALINA_HOME / webapps / logging / WEB-INF / classes directory of our web application. We need to get the path to the properties file before we can load it, so we get the full path to the web application on the filesystem and then append the name of the file. in this case, the name of the file comes from the properties initialization parameter specified in web.xml. This allows us to specify the location Of The Properties File Outside of the Application's Code: The property file is stored in a Web application's $ catalina_home / webapps / logging / web-inf / class directory, you must get its path before loading it, so this allow us to designate The location of the application code attribute file

// first We get the full weight qualified path to the Web Application

String path = getServletContext (). GetRealPath ("/");

String Properties = Path GetInitParameter ("Properties");

THE FINAL Step Is To Call The Configure () Method To Make The Logger Available for All The Other Files in The Application:

// Next We set the Properties for All the servlets and jsp

// Pages in this Web Application

PropertyConfigurator.configure (property);

}

The Final Methods Are Required To Be in Any Servlet:

// the dopost () Method Forwards All Requests to the doget () Method

Public Void Dopost (httpservletRequest Req, HttpservletResponse Resp) throws

ServletException, IOException {

Doget (REQ, RESP);

}

// the doget () Method Informs Users of the purpose of this servlet

Public void doget (HTTPSERVLETREQUEST REQ, HTTPSERVLETRESPONSE RESP) THROWS

ServletException, IOException {

PrintWriter out = Resp.getwriter ();

Out.println ("Initialization Servlet for Log4j);

}

Public void destroy () {}

}

Compile this class and place it in $ catalina_home / WebApps / logging / web-inf / class / wrox.web.xml

Next We need A Web.xml File for Our Web Application So That We can Specify The location:

Public "- // Sun microsystems, Inc.//dtd Web Application 2.3 // en"

"http://java.sun.com/dtd/web-app_2_3.dtd">

log4jinit

wrox.log4jinitservlet

Properties

Web-inf / class / log4j.properties

1

...................... ..

Logging to files

In this section We Will Start With a Simple File Example, Then Show The Following Formats That Are Made Available To Log4j:

HTMLFORMAT PATTERNFORMAT

SIMPLE FILE

The Configuration File for this First Example Is Very Similar To The One We Saw Before. However, this Time We'll log to the $ catalina_home / logs directory:

# A Simple Logger

Log4j.logger.wrox.simple = debug, Simple

# This Simple Example Will Log to a file

Log4j.appender.simple = org.apache.log4j.fileappender

Log4j.Appender.SIMPLE.FILE = /logs/log4jsimple.log

# We Will Use A Simple Layout for this Example

Log4j.Appender.SIMPLE.LAYOUG4J.SIMPLELAYOUT

Note that Log4j does not consider to be a shortcut;. It is merely a neat piece of notation for us Be sure and provide the full path in your files.Save this file as log4j.properties in logging / WEB-INF / Classes.

Finally, WE NEED A JSP page to use the logger (logsimple.jsp):

<% @ page import = "org.apache.log4j.logger"%>