superclass "javax.servlet.http.HttpServlet" not found on Java Build Path - solution

You might (normally) get the error following error on a dynamic java web project created through maven on Eclipse IDE. The solution is simple :
Error :
The superclass "javax.servlet.http.HttpServlet" was not found on the Java Build Path   
Error Location :
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
Solution 1)
Edit pom.xml to include servlet-api-x.x.jar in your dependencies:
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>javax.servlet-api</artifactId>
  <version>3.1.1</version>
  <scope>provided</scope>
</dependency>   
Solution 2)
Go to Project->Properties->Target Runtimes . And add your server container eg. : Apache Tomcat


change maven local repository path - symbolic links

Let's suppose we want to change the local maven repo path (default : c:\users\user_name\.m2\repository) to some other folder - lets say e:\repo  - so that the contents from e:\repo folder are mapped to the default folder location.

The following command creates a link folder "repository" in /.m2 folder and points to e:\REPO

C:\>mklink /d c:\users\gtiwari\.m2\repository e:\REPO


Note:

  • For more information about the mklink command visit : http://ganeshtiwaridotcomdotnp.blogspot.com/2014/08/using-symbolic-links-on-windows.html 
  • we can do it using other options as mentioned in http://stackoverflow.com/questions/71030/can-i-add-maven-repositories-in-the-command-line


using symbolic links on windows

Using symbolic links (MKLINK comand) on windows:

Suppose we want to create a link of folder 'e:\source' to c:\target\bridge then, use the following command:

C:\>mklink /d c:\target\bridge e:\source


  • This command creates a link folder "bridge" in c:\target\ where you can see the contents from e:\source.
For more info :
Visit: http://ss64.com/nt/mklink.html - 

grails detecting environment - groovy & gsp code

Grails/Groovy working code snippet to detect the current environment (development, test, production, or your  custom). Custom environment are defined in config.groovy file.

Detecting Environment in GSP code :

Following checks if current environment is other than production.
    <g:if test="${env != "production"}">
        //your logic 

    </g:if>

Detecting environment in Groovy Code ( in Controller, Service, etc..), using switch-case comparison

        switch(Environment.current.getName()){
            case "development":
                //do your stuff 1
                break;
            case "test":
                //do your stuff 2
                break;
            case "production":
                //do your stuff 3
                break;
            case "my_environment":  // for custom environment : my_environment
                //todo:
                break;
        }

Simple comparison in groovy

if(Environment.current.getName()=="development") {
    //do your stuff
}

Grails - auto login in spring security

Consider a typical web application where you have multiple user roles (like SUPER_ADMIN, OPERATOR, VISITOR etc ) and you need to do login and switch between them frequently. It certainly consumes a lot of time if you do this manually. One simple solution would be to use the browser's password remember feature. But this would not be useful if you need to switch between different role.

Here, I am going to do show how we can setup this mechanism in Grails applications which uses Spring Security plugin.

If you are using Spring Security plugin then, by default you will have following names for html textbox for username and password : j_username and j_password. and you have login request url as http://localhost:8080/YOUR_APP/j_spring_security_check .

The required login script :

Groovy Grails - Dynamic Method n Variable name and invoking them

Groovy allows to use dynamic method name and variable name and invoke/use them.

Dynamic Variable Names

Groovy allows to use variable name dynamically. To test this lets introduce a variable  "dogname" to Dog class

class Dog {
def dogname
...
}

//Testing dynamic variable name
        def aDog= new Dog()
aDog.name="Hachi"
def prop="dogname"

println aDog."$prop" // prints Hachi

git- saving username password - credential.helper cache - how to

Isn't is interesting if there is an option in GIT to save your credentials for short time so that you don't enter your username/password repeatedly each time when you do pull/push? Yes! there is an option introduced in GIT since 1.7.9 (released on January 2012). This method is more secure than permanently saving your username/password in   .git  file of your git clone directory.

So, run the following command at the GIT console (git bash) :
git config --global credential.helper cache
This caches the credentials for 15 minutes ( 900 seconds) by default. If you want a longer timeout period (say3600 seconds), you can do the following :
git config --global credential.helper 'cache --timeout=3600'

Grails - beginners video tutorial


From the Grails site: "Grails aims to bring the 'coding by convention' paradigm to Groovy. It's an open-source web application framework that leverages the Groovy language and complements Java Web development. You can use Grails as a standalone development environment that hides all configuration details or integrate your Java business logic. Grails aims to make development as simple as possible and hence should appeal to a wide range of developers not just those from the Java community."

grails- add jar to lib folder - not working - solution

In grails application you can add jar dependencies by just pasting the .jar file to lib folder. If your code doesn't find the jar dependency at runtime then you can do following :

Run the following grail command (s):
  • clean
  • compile --refresh-dependencies 
In eclipse you can open the Grails Command Prompt by :
Right Click on project -> Grail Tools -> Open Grails Command Prompt

Hope this helps.

nepali english date conversion logic - working java code


My friend Manoj has written about Nepali-English date conversion in this post. Take a look :

http://forjavaprogrammers.blogspot.com/2012/06/how-to-convert-english-date-to-nepali.html

He has explained the algorithm in detail about how to convert English dates into Nepali dates with java code.