Sunday, August 4, 2013
Monday, November 19, 2012
Implement Logging with log4j in Java Console Application using Eclipse IDE
4:22 PM
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Logging is a very
important part of programming that provides advanced debugging
capabilities and structured organisation of information recorded at the
run time. If I say debugging, you may ask "Why not System.out.println
(SOP)?". SOP is a powerful debugging technique that helps to
troubleshoot all the errors at the time of development. But when you
implement your application in a real time environment, unexpected
results and exceptions might occur. Logging provides you an effective
mechanism to track all the errors that occurs in your application after
you deploy it, so that you can understand what went wrong with your
application.
First step is to
define the log level. Log4j logs messages at six different levels. For
example, if you have a program that generates lot of warning messages
then you can ignore them by setting the log level to ERROR to avoid the
log file getting more clumsy. The log levels and the priority is as
follows,
Log4j is an
effective open source Logging API that is written in Java by the Apache
Software Foundation. All logging API's share a common architecture that
consists of three main components,
log4j Components |
1. Loggers: Loggers are responsible for capturing logging information
2. Appenders: Through appenders you tell the system on where to log the information such as files, database.etc.
3. Layouts: Layouts enable you to specify the format or displaying style of logging information.
In this post, I
am going to provide step by step instructions for implementing logging
with log4j in a simple Java Application using Eclipse IDE with
appropriate code and screenshots.
1. First of all download the latest version of log4j and unzip it.Locate log4j-xxx.jar file where xxx denotes the version of log4j release you have downloaded.
2. Open Eclipse IDE and create a Java Project and name it. In this example I have named it as "LoggingExample".
Explanation to the above configuration file
1. First of all download the latest version of log4j and unzip it.Locate log4j-xxx.jar file where xxx denotes the version of log4j release you have downloaded.
2. Open Eclipse IDE and create a Java Project and name it. In this example I have named it as "LoggingExample".
3. Create a
package under the default package, by right clicking on 'src' in Package
Explorer > New > Package, I have named this package as 'test'.
4. Next step is
to add the log4j-xxx.jar you have downloaded to the application you have
just created. To do this, right click on the project in Package
Explorer > Build Path > Configure Build Path
In the Java Build Path dialogue, go to Library tab, Click Add External JARs and add the log4j-xxx.jar > Click OK.
Now the log4j jar file is available to be used in your application.
5. Now create a
file named as "log4j.properties" in your default package where all your
source code is placed. This is the file that is going to hold all the
configuration settings for log4j implementation for all classes in your
application. To do this, right click the default package, in this case
'src' in package explorer > New > File >File Name:
log4j.properties
6. Copy the below code to the log4j.properties file you just created
# Log levels
log4j.rootLogger=INFO,CONSOLE,R
# Appender Configuration
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
# Pattern to output the caller's file name and line number
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n
# Rolling File Appender
log4j.appender.R=org.apache.log4j.RollingFileAppender
# Path and file name to store the log file
log4j.appender.R.File=./logs/testlog.log
log4j.appender.R.MaxFileSize=200KB
# Number of backup files
log4j.appender.R.MaxBackupIndex=2
# Layout for Rolling File Appender
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d - %c - %p - %m%n
Explanation to the above configuration file
TRACE < DEBUG < INFO < WARN < ERROR < FATAL
If you specify the log level as WARN, then the INFO, DEBUG and TRACE log level messages will be omitted while the WARN, ERROR and FATAL log level messages will be logged. In our example we have set the log level as DEBUG which means TRACE level logs will not be logged.
Next comes the appender settings. I have used two appenders, Console Appender and Rolling file appender. This means my log information will be displayed on the console as well as stored in a file. Since we have used RollingFileAppender, log4j will open a new file whenever the log file reaches the maximum file size of 200 KB mentioned in R.MaxFileSize property and the old one will be backed up. You can specify the number of backup files in the R.MaxBackupIndex property.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender log4j.appender.R=org.apache.log4j.RollingFileAppender
You can also use other appenders, like JDBCAppender,SocketAppender,SysLogAppender etc. according to your requirement to route the logging information to appropriate destinations.
Each appender is associated with layout settings that specifies the format of information that is being logged. I have used PatternLayout for both the appenders and have defined two different patterns for each of them. For console appender,
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n
where,
%5p - Priority of the logging event
%t - Name of the thread that initiated the logging event
%F- File name where the logging issue was requested
%L - line number that caused the logging message to be generated
Sample output of the above layout:
WARN [main] (Main.java:14) - Variable is not initiated!
You can also use other layouts such as HTMLLayout, DateLayout, XMLLayout etc.
7. Last step is
to incorporate logging in your java class. To do this, Create a Class in
the package you have created in Step 3. Right Click the package >
New > Class > Class Name: LoggingSample.java
Now Copy and Paste the below code in LogginSample.java class.
package test;
import org.apache.log4j.Logger;
import java.io.*;
public class LoggingSample {
private static Logger logger=Logger.getLogger("LoggingExample");
public static void main(String[] args){
try{
FileInputStream fstream =
new FileInputStream("D:\\textfile.txt");
DataInputStream in =
new DataInputStream(fstream);
BufferedReader br =
new BufferedReader(new InputStreamReader(in));
String strLine;
while ((strLine = br.readLine()) != null){
System.out.println (strLine);
}
in.close();
}catch (FileNotFoundException fe){
logger.error("File Not Found",fe);
logger.warn("This is a warning message");
logger.trace("This message will not be logged since log
level is set as DEBUG");
}catch (IOException e){
logger.error("IOEXception occured:", e);
}
}
}
In the above code I am trying to read a file which does not exist. The log that is generated
on the console is,
on the console is,
ERROR [main] (LoggingSample.java:19) - File Not Found
java.io.FileNotFoundException: D:\textfile.txt (The system cannot find the file specified)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at java.io.FileInputStream.<init>(Unknown Source)
at test.LoggingSample.main(LoggingSample.java:10)
WARN [main] (LoggingSample.java:20) - This is a warning message
WARN [main] (LoggingSample.java:20) - This is a warning message
At the same time log file is generated at \workspace\LoggingExample\logs\testlog.log with the following content,
2012-07-21 23:58:21,694 - LoggingExample - ERROR - File Not Found
java.io.FileNotFoundException: D:\textfile.txt (The system cannot find the file specified)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at java.io.FileInputStream.<init>(Unknown Source)
at test.LoggingSample.main(LoggingSample.java:10)
2012-07-21 23:58:21,699 - LoggingExample - WARN - This is a warning message
Please note that in the above output, TRACE level message is not generated since it's priority is lower than that of DEBUG level which we have set in our log4j.properties file, while WARN level message is logged since it's priority is higher than that of DEBUG level.
Keyboard shortcuts to Java IDEs
4:21 PM
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This
blog is about useful keyboard shortcuts for Top 5 Java IDEs. Java is an highly
scalable and platform independent programming language, which is used by almost
every programmer in the world. Since it comes under open source category it has
always been the first choice for every programmer around the world. Hence,
knowing the keyboard shortcuts for the Java IDE of your choice will not only
increase your productivity but will give you more time for the things you like
to do. Here I have listed about some useful keyboard shortcuts for 5 most used
Java IDEs.
Let me
first list out the top 5 Java IDEs,
- NetBeans
- Eclipse
- IntelliJ IDEA
- My Eclipse
- IBM RAD
NetBeans Shortcuts
- Ctrl-Space Code completion
- Esc Close code completion
- Shift-Space Enter a space without expanding an abbreviation
- Alt-F1 Display Javadoc
- Shift-F1 Search Javadoc
- Alt-Shift-I Import class
- Alt-G Go to declaration
- Alt-O Go to source
- Crtl-; Add semicolon to the line on cursor
- F9 Compile selected file/package
- Ctrl-Shift-F9 Compile project
- Alt-Shift-C Stop compilation
- F6 Run selected file
- Ctrl-Shift-F6 Run project
Eclipse Shortcuts
- Ctrl-1 Quick fix errors
- Ctrl-T Find class (From jar files also)
- Ctrl-R Find resource files
- Ctrl-Shift-O Organize imports
- F3 Go to declaration
- Ctrl-/ Commenting and Uncommenting lines
- Ctrl-Shift-F Text Formatting
- Ctrl-E Switch to other open editors
- Ctrl-W Close current file
- Ctrl-D Delete a line
- Ctrl-Q Go to last modified line
IntelliJ IDEA Shortcuts
- Alt-F1 Switch between views(Project,Structure.etc)
- Alt-Home Show Navigation Bar
- Ctrl-J Insert a live template
- Alt-Enter Quick fix
- Ctrl-Space Invoke Code Completion
- Ctrl-N Find Class by name
- Ctrl-D Duplicate the current line or selection
- Ctrl-Shift-Enter Smart Statement Completion
MyEclipse Shortcuts
- Shift-Ctrl-E Switch to Editor
- Ctrl-F10 Show view menu
- Shift-Ctrl-/ Add Block comment
- Shift-Ctrl-M Add Import
- Shift-Alt-J Add Javadoc comment
- Ctrl-F11 Run
- F3 Open Declaration
- Shift-F2 Open attached JavaDoc
- Ctrl-1 Quick Fix
- Alt-/ Word Completion
- Ctrl+B Build All
IBM RAD Shortcuts
- Ctrl-1 Quick Fix
- Ctrl-/ Comment
- Ctrl-\ Uncomment
- Ctrl-E Next Problem
- Ctrl-Shift-E Previous Problem
- Ctrl-F11 Run
- Ctrl-U Run Snippet
- Ctrl-Space Content Assist
AJAX with Servlets using JQuery and JSON
4:20 PM
1 Comment
In my previous post, I
explained about making AJAX calls to a servlet from a JSP page and updating a
part of the JSP page with the response from the Servlet. That was a very simple
example I provided in that post by returning a piece of text from the servlet
to JSP to start with, and now in this post I am going to add something more to
it by making the servlet return complex Java Objects such as lists, maps, etc.
To do this, let us get introduced to JSON(Javascript
Object Notation), in addition to JQuery and AJAX. JSON is derived from
Javascript for representing simple data structures and associative arrays,
called objects. Here in our scenario, we are going to use a JSON library in Servlet
to convert Java objects (lists,maps,arrays.etc) to JSON strings that will be
parsed by JQuery in the JSP page and will be displayed on the web page.
There are many JSON libraries available that can be used to
pass AJAX updates between the server and the client. I am going to use google's
gson library in this example.
Now, let us create a simple JSP page with two drop down
lists, one that contains values for countries and the other that is going to be
populated with values for states based on the value of country selected in the
first drop down list. Whenever the value is selected in the "country"
drop down list, the "states" drop down list will be populated with
corresponding state values based on the country selected. This has to be done
without a page refresh, by making AJAX calls to the servlet on the drop down
list change event.
Here are the steps to reproduce in Eclipse,
1. First of all create a "Dynamic Web Project" in
Eclipse.
2. Create a new JSP page under "Webcontent" folder
and copy paste the below code in it.
<%@ 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>AJAX calls to Servlet using
JQuery and JSON</title>
<script
src="http://code.jquery.com/jquery-latest.min.js"></script>
<script>
$(document).ready(function() {
$('#country').change(function(event) {
var
$country=$("select#country").val();
$.get('ActionServlet',{countryname:$country},function(responseJson) {
var
$select = $('#states');
$select.find('option').remove();
$.each(responseJson, function(key, value) {
$('<option>').val(key).text(value).appendTo($select);
});
});
});
});
</script>
</head>
<body>
<h1>AJAX calls to Servlet using
JQuery and JSON</h1>
Select Country:
<select id="country">
<option>Select
Country</option>
<option value="India">India</option>
<option
value="US">US</option>
</select>
<br/>
<br/>
Select State:
<select id="states">
<option>Select State</option>
</select>
</body>
</html>
3. Download google's GSON library from here and place it in your project's WEB-INF/lib
folder.
4. Create a servlet in the name 'ActionServlet' (since I
have used this name in the jquery code above') in the src directory. Copy and
paste the below code in the doGet() method of the servlet and add the import
statement in the header section of the servlet.
import com.google.gson.Gson;
protected void doGet(HttpServletRequest
request, HttpServletResponse response) throws ServletException,
IOException {
String
country=request.getParameter("countryname");
Map<String, String> ind = new
LinkedHashMap<String, String>();
ind.put("1", "New
delhi");
ind.put("2", "Tamil
Nadu");
ind.put("3",
"Kerala");
ind.put("4", "Andhra
Pradesh");
Map<String, String> us = new
LinkedHashMap<String, String>();
us.put("1",
"Washington");
us.put("2",
"California");
us.put("3",
"Florida");
us.put("4", "New
York");
String json = null ;
if(country.equals("India")){
json=
new Gson().toJson(ind);
}
else
if(country.equals("US")){
json=new
Gson().toJson(us);
}
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
response.getWriter().write(json);
}
}
In the above code, we create two maps for two countries, and
return the one based on the country parameter passed to the servlet in the AJAX
call made by the JQuery's get() method. Here we convert the map objects to json
strings in order to send the response back to the JSP page.
5. Make sure you have done servlet mapping properly in
web.xml file. An example of this is given below,
<servlet>
<servlet-name>ActionServlet</servlet-name>
<servlet-class>ajaxdemo.ActionServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ActionServlet</servlet-name>
<url-pattern>/ActionServlet/*</url-pattern>
</servlet-mapping>
In the above code,'ajaxdemo' is the package name in which I
have created the servlet. Replace it with your package structure to make the
servlet work properly.
Thats it! You are now all set to run the project with
Tomcat. When you run this project, the second drop down list will be populated
automatically when you change the value in the first drop down list.
Output Screenshots:
First drop down list changing,
On selecting 'India' in the first drop down list,
On selecting 'US' in the first drop down list,
Please leave your comments
and queries about this post in the comment sections in order for me to improve
my writing skills and to showcase more useful posts.