Debug JSP Using Java Logger, Println statements & Debugging tools

Debugging in JSP

  •  
  • Debugging is the process to trace the error in the application. It is not very easy to trace bugs and error in the application.
  • JSP applications are client interactive. Hence, errors are difficult to reproduce.
  • In this tutorial, you will learn-
  • JSP Debugging Methods
  • Using println statements
  • Using Java Logger
  • Using debugging tools
  • JSP Debugging Methods
  • There are different ways through which we can debug an application:
  • Using println statements
  • Using Java Logger
  • Using Debugger tools
  • Using println statements:
  • System.out.println() is used to trace whether certain part is executed or not.
  • We can print the variables in the code.
  • Also, we can print values which need to be used to debug the application.
  • Example:
  • In this example, we are debugging through the println statements to understand what values we are getting for the variables.
  • <%@ page language=“java” contentType=“text/html; charset=ISO-8859-1”
  • pageEncoding=“ISO-8859-1”%>
  • <!DOCTYPE html PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN” “http://www.w3.org/TR/html4/loose.dtd”>
  • <html>
  • <head>
  • <meta http-equiv=“Content-Type” content=“text/html; charset=ISO-8859-1”>
  • <title>Debug Guru JSP</title>
  • </head>
  • <body>
  • <% int num1=10;
  • System.out.println(“This is debugging Guru JSP”);
  • num1++;
  • int num2=num1/0;
  • System.out.println(num2);%>
  • </body>
  • </html>
  • Explanation of the code:
  • Code Line 10: We are taking variable num1 and initializing it to 10.
  • Code Line 11: We are printing using println statements that “This is debugging Guru JSP” to debug which line of code has been executed
  • Code Line 12: Here we are incrementing the variable num1 with 1.
  • Code Line 13: we are dividing the num1 by 0 and putting into a new variable num2.
  • Code Line 14: As we want to know the value for num2 we can fetch using the println statement to know till which line of code has been executed.
  • When you execute the above code, you get the following output:
  • Debug JSP Using Java Logger, Println statements & Debugging tools
  • Output:
  • Here, we are getting the statement “This is debugging Guru JSP” with the value of the variable num1 which has been incremented hence 11.
  • Using Java Logger
  • The Java logging framework is used for logging services for any class running in JVM.
  • This is used to log any information from the code.
  • It logs all necessary information to trace the bugs which have occurred.
  • Example:
  • In this example, we are using java logger to trace the information in the code.
  • Messages can be shown using different functions like severe(), warning(), info(), config(). Fine()
  • Info is used to show the information in the log file .
  • Severe is used to show some severe information on the log file.
  • <%@taglib prefix=“guru” uri=“http://java.sun.com/jsp/jstl/core” %>
  • <%@page import=“java.util.logging.Logger” %>
  • <%@page import=“java.util.Date” %>
  • <%@ page language=“java” contentType=“text/html; charset=ISO-8859-1”
  • pageEncoding=“ISO-8859-1”%>
  • <!DOCTYPE html PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN” “http://www.w3.org/TR/html4/loose.dtd”>
  • <html>
  • <head>
  • <meta http-equiv=“Content-Type” content=“text/html; charset=ISO-8859-1”>
  • <title>Debugging Guru JSP</title>
  • </head>
  • <body>
  • <% Logger logger=Logger.getLogger(this.getClass().getName());%>
  • <% Date dt = new Date();
  • logger.info(dt.toString());
  • logger.info(“This is Guru Logging debugger”); %>
  • </body>
  • </html>
  • Explanation of the code:
  • Code Line 2: We are importing the java logger to log the information.
  • Code Line 3: We are importing Date class of the util package
  • Code Line 13: We are initializing the logger class by using getLogger method.
  • Code Line 14: We are initializing the date class.
  • Code Line 15: we are using the info method of logger class object to print the current date.
  • Code Line 16: We are using the info method to print ‘This is Guru Logging debugger’.
  • When you execute the above code, you will get the following output
  • Debug JSP Using Java Logger, Println statements & Debugging tools
  • Output:
  • We will get the output in std.log, which will store in Logging folder in the server. Here we will get the information which has been written in the code.
  • Using debugging tools:
  • We have been using eclipse since the beginning of the tutorial. In eclipse, we have debugging tools to debug the errors or bugs in the code.
  • To debug the application we have following points:
  • Set the breakpoint
  • Restart server in debugging mode
  • Debug through breakpoints.
  • Set the breakpoint:
  • We can set the breakpoint in the code, where we want to trace the code:
  • <%@ page language=“java” contentType=“text/html; charset=ISO-8859-1”
  • pageEncoding=“ISO-8859-1”%>
  • <!DOCTYPE html PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN” “http://www.w3.org/TR/html4/loose.dtd”>
  • <html>
  • <head>
  • <meta http-equiv=“Content-Type” content=“text/html; charset=ISO-8859-1”>
  • <title>Debugging Guru JSP</title>
  • </head>
  • <body>
  • <% String name = “This is test Guru JSP”;
  • out.println(name);
  • %>
  • </body>
  • </html>
  • Here we are setting the breakpoint as ‘toggle breakpoint’ when you right click on the project explorer. We can set the breakpoints where the error or bug is occurring.
  • Once they are set, the debugger will move to the first breakpoint and then next and so on. It will run through the application with the help of breakpoints.
  • After setting the breakpoint, we need to restart the server in debug mode.
  • Restart server in debugging mode:
  • We can restart the server in debugging by clicking on the server side and click on start in debug mode.
  • Debug JSP Using Java Logger, Println statements & Debugging tools
  • Debug through breakpoints:
  • We can debug the application by clicking on the application as debug as:
  • Debug JSP Using Java Logger, Println statements & Debugging tools
  • You get an alert to switch the perspective then click “Yes” button.
  • After clicking ‘yes’ button we will get the following perspective:
  1. Debug JSP Using Java Logger, Println statements & Debugging tools

    We will get the variables tab, where we can see values of the variables:

    Debug JSP Using Java Logger, Println statements & Debugging tools

    The breakpoints tab shows number of breakpoints in the code:

    Debug JSP Using Java Logger, Println statements & Debugging tools

    We can debug the application through the breakpoints which have been set.

    Summary:

  • We have learnt about debugging in JSP.
  • We have also used println statements, Java Logger and Debugging tools.
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