vincentkong.com » Java

NekoBean Paper Craft

Vincent Kong — Wed, 27 Jan 2010 02:46:19 +0000

A few weeks ago, I stumbled on a paper craft template of NekoBean on the nekobean.net website. The last time I did any art and craft was in junior public school, so I definitely didn’t have the talent for this kind of work.

I printed a few copies using the laser printer at work, and went to work using some white glue and a pair of scissors.

After a few failed attempts and numerous hours I finally put it together!

NekoBean Paper Craft

For readers who aren’t geeks…

What is NekoBean? NekoBean is the mascot for NetBeans introduced by the NetBeans Japanese Speaking Community in Mar 2008. The actual author is Mutsuki san who seems to be a very talented designer. The mascot is derived from a cat (“Neko” means “cat” in Japanese), and the NetBeans grid/box logo.

What is NetBeans? Without being too technical, NetBeans is a free software development tool for programming Java, and other programming languages.

If-Else in Ant

Vincent Kong — Mon, 18 Jan 2010 00:59:31 +0000

When I need to write quick script to perform a simple task, I opt to use Ant instead of a shell script. Unfortunately, the Ant core tasks doesn’t provide any flow logic like the everyday if-else statements.

Ant-Contrib provides a collection of useful tasks missing in the Ant core.

Installing Ant-Contrib

There are 2 methods to install ant-contrib:

Copy ant-contrib-1.0b3.jar to the lib directory of your Ant installation. If you want to use one of the tasks in your own project, add the lines

Keep ant-contrib-1.0b3.jar in a separate location. You now have to tell Ant explicitly where to find it e.g. a lib directory relative to the build.xml

Example Using If-Else Task


  
  
    [...]
  
  
    [...]

SSH with a Web Browser

Vincent Kong — Wed, 24 Dec 2008 07:32:03 +0000

A while back, I was using someone’s computer and I wanted to SSH into my server. The machine didn’t have any SSH client and I didn’t have my U3 Smart Drive with me.

MindTerm is a client that implements the SSH protocols written in Java which can run as an Applet. The basic syntax for embedding the MindTerm Applet in a web page is as follows:

Due to the Java security model, the Applet requires to be sign, otherwise it won’t run properly and throw an AccessControlException, as shown in the Java console.

For information on how to sign an Applet refer to Signing Java Applets Using RSA Certificate. After the Applet has been successfully signed a pop up will appear asking to accept the digital signature, and when accepted the Applet will have permission to run properly; this can be verify with the Java console again.

Now you can SSH from any computer that has a web browser and internet access.

For more information refer to Running MindTerm as an Applet

Sending Email with Ant

Vincent Kong — Tue, 16 Dec 2008 02:19:44 +0000

Sometimes it’s useful for an Ant script to send out an email. This can be easily done using the mail task which is part of the Core Tasks in Ant. Before using the mail task, the JavaBean Activiation Framework jar file (activation.jar), and JavaMail jar file (mail.jar) needs to be copied into the Ant lib directory. Here is a mail task example which sends an email using a GMail account.


  
    Example email sent by Ant Mail task.

Troubleshooting Ant mail task in Ubuntu

Failed to initialise MIME mail: org.apache.tools.ant.taskdefs.email.MimeMailer not found in java.net.URLClassLoader

If you downloaded Ant from the Ubuntu packages repository, not all the core Ant tasks are available. Download and extract Ant from the Apache Ant website.

$ wget http://www.apache.org/dist/ant/binaries/apache-ant-1.7.0-bin.tar.gz $ tar -zxvf apache-ant-1.7.0-bin.tar.gz

Copy the ant-javamail.jar into the lib directory of the Ubuntu Ant installation

$ cp ./apache-ant-1.7.0/lib/ant-javamail.jar /usr/share/ant/lib

Failed to send email: could not instantiate ssl security provider, check that you have JSSE in your classpath

If the ssl attribute is set to true, then the Java Secure Socket Extension (jsse.jar) jar file is required, which is already part of J2SE 1.4.x and later. Ubuntu uses GNU Compiler for Java (gcj) as the default JVM which doesn’t have JSSE as the part of the distribution, therefore the jsse.jar file needs to be copied into the Ant lib directory. An alternative solution is to set the default JVM to use another Java distribution which already has JSSE bundled.

Problem using MySQL JDBC on Tomcat 5.5 and Ubuntu 8.04

Vincent Kong — Wed, 05 Nov 2008 03:36:39 +0000

Normally when I build a web application that connects to a MySQL database, I would place the mysql-connector-java-bin.jar file into the WEB-INF/lib of the web application.

However, when I deployed the application on Tomcat 5.5 on Ubuntu 8.04 I got an exception: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

I couldn’t find the reason which caused the exception, so I did a quick fix by placing the jar file into the Tomcat’s common lib directory.

$ cp mysql-connector-java-bin.jar /usr/share/java $ cd /usr/share/tomcat5.5/common/lib $ ln -s ../../../java/mysql-connector-java-bin.jar mysql-connector-java-bin.jar

Signing Java Applets Using RSA Certificate

Vincent Kong — Tue, 19 Feb 2008 16:00:15 +0000

Generate a private/public key pair with the RSA algorithm.
$ keytool -genkey -keyalg rsa -alias keyname Enter keystore password: password What is your first and last name? [Unknown]: What is the name of your organizational unit? [Unknown]: What is the name of your organization? [Unknown]: What is the name of your City or Locality? [Unknown]: What is the name of your State or Province? [Unknown]: What is the two-letter country code for this unit? [Unknown]: Is CN=Unknown, OU=Unknown, O=Unknown, L=Unknown, ST=Unknown, C=Unknown correct? [no]:

Enter key password for
(RETURN if same as keystore password):
Generate the self-signed certificate containing the public key, valid for one year.
$ keytool -selfcert -alias keyname -validity 365 Enter keystore password: password
Use jarsigner to sign the JAR file, using the RSA credentials in your keystore that were generated in the previous steps. Make sure the same alias name is specified.
$ jarsigner MyApplet.jar keyname Enter Passphrase for keystore: password
Verify the JAR file.
$ jarsigner -verify -verbose -certs MyApplet.jar

s = signature was verified
m = entry is listed in manifest
k = at least one certificate was found in keystore
i = at least one certificate was found in identity scope

jar verified.
Your applet has been signed properly. You are now ready to deploy your RSA signed applet.

Setting Up Log4j Quickstart Guide

Vincent Kong — Wed, 13 Jun 2007 15:57:09 +0000

Log4j is an open source tool developed for putting log statements into your Java application. It’s allows log statements to remain in shipped code while giving the user the ability to enable logging at runtime without modifying any of the application binary.

The easiest way to setup Log4j is to create a log4j.properties file and put in root of your classes directory. A typical example of the log4j.properties file is as follows:

# Set root logger level to INFO and log to console, and log file appender.
log4j.rootLogger=INFO, Console, LogFile
# Set the logger level to DEBUG for all classes under the package com.mycompany.
log4j.logger.com.mycompany=DEBUG
# Define the settings for the console appender.
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=%d{ISO8601} [%t] %-5p %C - %m%n
# Define the settings for the log file appender.
# Log file rotates every month.
log4j.appender.LogFile=org.apache.log4j.DailyRollingFileAppender
log4j.appender.LogFile.DatePattern='.'yyyy-MM
# Location to where the log file exists.
log4j.appender.LogFile.file=/path/to/logfile.log
log4j.appender.LogFile.layout=org.apache.log4j.PatternLayout
log4j.appender.LogFile.layout.ConversionPattern=%d{ISO8601} [%t] %-5p %C - %m%n

The ConversionPattern determines what the format of each line logged:

%d{ISO8601} Output the date in ISO8601 format.
%t Output the thread that generated the logging event.
%-5p Output the priority of the logging event left
justified to a width of five characters.
%C Output the fully qualified class name of the caller
issuing the logging request.
%m Output the application supplied message associated with
the logging event.
%n Output the platform dependent line separator character or
characters. e.g “\n” or “\n\r”

For more information refer to the Log4j documentation

Setting Default JVM in Ubuntu

Vincent Kong — Mon, 11 Jun 2007 15:56:03 +0000

There are circumstances where you may need to have more than one version of Java installed, but how do you switch between them?

Execute the following command to list the installed JVMs:

$ sudo update-alternatives --config java

Simply enter the number for the JVM to use. The * shows the current selected JVM.

Java Code Snippet for Sending Email using Gmail SMTP Server

Vincent Kong — Thu, 07 Jun 2007 15:53:35 +0000

The partial code below shows how to sent an email using the Gmail’s SMTP server:

Properties properites = new Properties();

properties.put("mail.smtp.host", "smtp.gmail.com");
properties.put("mail.smtp.port", "25");
properties.put("mail.smtp.auth", "true");
properties.put("mail.smtp.starttls.enable", "true");
properties.put("mail.smtp.socketFactory.port", "465");
properties.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
properties.put("mail.smtp.socketFactory.fallback", "false");

Session session = Session.getInstance(properties, new Authenticator() {
      public PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication("username@gmail.com", "password");
      }
});

Message msg = new MimeMessage(session);
msg.setFrom(...);
msg.addRecipient(...);
msg.setSubject(...);
msg.setText(...);

Transport.sent(msg);

Java Code Snippet for Parsing Strings into Date

Vincent Kong — Thu, 07 Jun 2007 15:50:52 +0000

SimpleDateFormat formatter = new SimpleDateFormat ("yyyy-MM-dd"); String input = "2007-05-04"; Date d; try { d = formatter.parse(input); } catch (ParseException e) { e.printStackTrace(); } Related posts:Java Code Snippet for Sending Email using Gmail SMTP Server Signing Java Applets Using RSA Certificate Installing TinyMCE Editor in Drupal Related posts: