Tag: java

Java temporary file directory path

I’ve recently resurrected some old java code that I’d written back when I primarily used Windows instead of Ubuntu for development. In some of that legacy code, the temporary file paths were hardcoded, to make things more modern and portable, The following line is recommended to get the Operating System values regardless of where it is installed and ran. The file separator “slash” can also be determined in this manner.


private static final String TMPDIR = System.getProperty("java.io.tmpdir") + java.io.File.separatorChar;

Add SonarQube Analysis to Eclipse

If you have already embraced Continuous Inspection with Sonar/SonarQube, you may find it advantageous to do analysis of new or modified code within the IDE without having to wait for a new build/compile/analyze cycle. Additionally, it’s often faster to keep all of your required information within the IDE without having to also open a web browser.

You can easily add this capability:

  1. Help > Install New Software… > Add… > then enter:
  2. http://dist.sonar-ide.codehaus.org/eclipse/
  3. Restart Eclipse
  4. RightClick on project – Configure > Associate with SonarQube > chose project

REFERENCES:

Eclipse compiler error when using sun.misc.Base64Encoder reference

I’ve recently been doing some work with code that is still running in a Java5 environment, to make matters worse, no new libraries can be added to the application. With these restrictions, I’ve had to resort to using only functions available in the standard installed JVM. The code relies on HTTP Basic authentication, and thus needs to use Base64 encoding.

The following classes were to be used…

import sun.misc.BASE64Encoder;
import sun.misc.BASE64Decoder;

Unfortunately, Eclipse did not like this and gave an error…

Access restriction: The type BASE64Decoder is not accessible due to restriction on required library C:\jdk1.5.0_22\jre\lib\rt.jar

Thankfully, this class (while not recommended, is in every build of the JVM that I have seen), you can tell Eclipse to only ‘Warning’ on it’s usage…

Window -> Preferences -> Java -> Compiler -> Error/Warnings.
Select Deprecated and Restricted API. Change it to warning.
Change Forbidden and Discouraged Reference and change it to Warning, or as needed.

BTW, I would normally rely on the commons-codec.jar for this functionality, and use org.apache.commons.codec.binary.Base64 for this purpose.

REFERENCES:

Enable larger file uploads via Tomcat manager

Shortly after I automated code deployments in my Tomcat7 development testing environment, I found that some larger builds began failing with the following error:


org.apache.tomcat.util.http.fileupload.FileUploadBase$SizeLimitExceededException: the request was rejected because its size (...) exceeds the configured maximum (62428800)

After a little digging, I found that the WAR files were exceeding the default maximum upload size, thankfully, this is trivial to increase.


sudo vi /usr/share/tomcat7-admin/manager/WEB-INF/web.xml

(Change 52428800 to a larger number, perhaps doubled like 104857600)

<multipart-config
<!-- 50MB max = 52428800 (100MB = 104857600) -->
<max-file-size>104857600</max-file-size>
<max-request-size>104857600</max-request-size>
<file-size-threshold>0</file-size-threshold>
</multipart-config>

REFERENCES:

Install SonarQube for Continous Inspection

Installation of Sonar requires but a few simple steps, though they can be rather obscure to many developers.

Connect to MySQL:

  1. CREATE DATABASE sonar CHARACTER SET utf8 COLLATE utf8_general_ci;
  2. grant all privileges on sonar.* to 'sonar@localhost' identified by 'sonar';
  3. flush privileges;

Easiest method, if you are on Ubuntu:

  1. sudo vi /etc/apt/sources.list
  2. Then add the following line:
    deb http://downloads.sourceforge.net/project/sonar-pkg/deb binary/
  3. sudo apt-get update
  4. sudo apt-get install sonar
  5. You will then have to stop/start as above to edit the configuration, generally to change database config:
    sudo vi /opt/sonar/conf/sonar.properties

Manual installation (and upgrade?) if you prefer to do things the hard way 🙂

  1. Download and unzip the release:
    wget http://dist.sonar.codehaus.org/sonar-3.6.1.zip
    unzip sonar-3.6.1.zip
    sudo mv sonar-3.6.1 /opt/sonar
    sudo rm -r /opt/sonar (to remove old link)
    sudo ln -s /opt/sonar-3.6.1/ /opt/sonar
  2. cd /opt/sonar/conf
  3. vi sonar.properties
    (uncomment lines for MySQL, comment out H2)
  4. sudo cp /opt/sonar/bin/linux-x86-64/sonar.sh /etc/init.d/sonar
  5. sudo vi /etc/init.d/sonar
    add the following 2 lines:
    SONAR_HOME=/opt/sonar
    PLATFORM=linux-x86-64

    change:
    WRAPPER_CMD="${SONAR_HOME}/bin/${PLATFORM}/wrapper"
    WRAPPER_CONF="${SONAR_HOME}/conf/wrapper.conf"
    PIDDIR="/var/run"

  6. sudo update-rc.d -f sonar remove
  7. sudo chmod 755 /etc/init.d/sonar
  8. sudo update-rc.d sonar defaults
  9. /etc/init.d/sonar start

REFERENCES:

Upgrades can be a little odd, if you see the maintenance page at http://localhost:9000/maintenance, go to http://localhost:9000/setup and do the required steps.

REFERENCES:

Device Fingerprinting

Often it can be beneficial to ‘more’ uniquely identify your users. For applications this is trivial, but in a web browser this can be accomplished via only a few attributes.

  • HTTP – User-Agent, IP Address, Content types and languages accepted.
  • HTTPS/SSL – the keys and encryption methods available to a specific user may vary for each client configuration.
  • HTML5 – local storage and capabilities supported.
  • Geolocation – this is included in HTML5, but also supported in many clients without full HTML5 support, or via browser extensions.
  • JavaScript – Installed version – and many DOM attributes/capabilities such as timezone, installed plugins, screen sizes and fonts from the browser can be detected.
  • Java (Applet) – Installed version – this can often be used to get additional information regarding the client system directly from the VM or Operating System itself. (* Persistent Cookies possible)
  • Flash – Installed version – this can often be used to get additional information regarding the client system directly from the Operating System itself. (* Persistent Cookies possible)
  • Silverlight (for Microsoft Windows) – – Installed version and additional information from Operating System?
  • GoogleGEARS (deprecated) – Installed version and additional information from Operating System such as Geolocation

REFERENCES:

Automatically update Java on Ubuntu Linux

With the rate of updates and security patches for Java, administration of your Ubuntu machines can become tedious. There’s a better way… allow it to check for and update with your other software. The steps are easy…


sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer

NOTE: You can also install java8 in the same manner with:
sudo apt-get install oracle-java8-installer

NOTE: The Java Control Panel can sometimes be hard to locate, it will be at the following:
/usr/lib/jvm/java-7-oracle/bin/ControlPanel

REFERENCES:

NetBeans jdkhome error

After updating the JDK on my development workstations, NetBeans started reporting the following at each start up.

Cannot locate java installation in specified jdkhome:
C:\Program Files\Java\jdk1.7.0_04
Do you want to try to use default version?
[ Yes | No ]

Thankfully, after a little searching, I found that the solution is very simple. You can change the value or comment it out with a # in:
C:\Program Files\NetBeans #.#.#\etc\netbeans.conf

netbeans_jdkhome="C:\Program Files\Java\jdk1.7.0_04”

REFERENCES:

JavaScript language attribute

Occasionally I’ve stumbled upon legacy javascript code that is used to determine javascript support by the visiting users. This often proves comical, because they are many times wasting time making checks for some “VERY OLD” browsers indeed! Here’s a rundown of the versions of javascript as well as their release dates and some common browser versions that implemented them.

  • JavaScript 1.0 (March 1996) = Navigator 2.0 / MSIE 3.0
  • JavaScript 1.1 (August 1996) = Navigator 3.0
  • JavaScript 1.2 (June 1997) = Navigator 4.0-4.05
  • JavaScript 1.3 (October 1998) = Navigator 4.06-4.7x / MSIE 4.0
  • JavaScript 1.4 = Netscape Server
  • JavaScript 1.5 (November 2000) = Navigator 6.0 / Firefox 1.0 / MSIE 5.5 – 8.0 / Safari 3.0-5 / Chrome 1.0-10.x / Opera 6.0
  • JavaScript 1.6 (November 2005) = Firefox 1.5
  • JavaScript 1.7 (October 2006) = Firefox 2.0
  • JavaScript 1.8 (June 2008) = Firefox 3.0 / Opera 11.50
  • JavaScript 1.8.1 = Firefox 3.5
  • JavaScript 1.8.2 (June 2009) = Firefox 3.6
  • JavaScript 1.8.5 (July 2010) = Firefox 4.0 / MSIE 9.0 / Opera 11.60

The language attribute has long been deprecated and should generally be avoided, it’s original purpose was to support other scripting languages, notably VBScript, or particular JavaScript versions. Modern conventions rely on specifying the MIME type instead via the ‘type’ attribute.

<SCRIPT LANGUAGE="JavaScript"> is now <script type="text/javascript">

<SCRIPT LANGUAGE="JavaScript1.1"> is now <script type="text/javascript1.1">

<SCRIPT LANGUAGE="VBScript"> is now <script type="text/vbscript">

<SCRIPT LANGUAGE="TCL"> is now <script type="text/tcl">

REFERENCES:

Ternary Operators and Assignment

Ternary operators, if not abused, can make code easier to follow once you grasp the concept. While normally used for assignment, they can also be used to control program flow. The keys to this are the condition, question mark and colon that identify the condition and results.


var foo = (some_condition) ? then_code : else_code;

REFERENCES: