MySQL ERROR - Specified key was too long; max key length is 767 bytes

This is very old MySQL issue. MySQL engine like InnoDB or MyISAM has their own limit on the length of the columns where indexing can be applied. Usually it is 1000 for MyISAM and 767 for InnoDB. Problem occures when user try to change the length of the column where indexing was already applied or try to implement indexing on a column where length of column is already greater than 1000.
This problem can be solved in two ways:

1. Set the properties of MySQL engine. (It will only work for mysql 5.6+).

• show engines;(Get the current Engine - Only to check).
• show variables like 'innodb%'; (Get current engines properties)
• Set properties as:
• innodb_large_prefix=on;
• innodb_file_format=barracuda;
• innodb_file_per_table=true;
• Run the alter command.

2. Set MySQL to no engine mode.

• SELECT @@SESSION.sql_mode; (Check current SQL mode)
• SET sql_mode = 'NO_ENGINE_SUBSTITUTION'; (Set SQL mode to no engine)
• run your alter command.
• Again set back to engine mode

Exceptions with method overriding in java

In java methods can throw the different checked/unchecked exceptions, this seems to be simple as long as we are talking about the single methods in java but when we deal with method overriding in java the concept of exception which can be thrown by overriding or overridden method are bit tricky. The overriding method cannot throw the new/broader exception than the overridden method is throwing but this case is only true for checked exception and not true for unchecked/runtime exception.

If overriding method is throwing a checked exception which is new/broader than your overridden method exception then your code will not compile.

The combination of base class overridden method and derived class overriding method with respect to exceptions can be categorized into the below five cases as:

1.    Base class method throwing no exception and derived class method is throwing exception.
       •    In case of checked exception code will not compile
       •    In case of runtimeException code will work fine.

2.    Base class method throwing less newer/broader exception than derived class method is throwing.   
       Suppose base class overridden method is throwing ArithmeticException and derived class overriding
       method is throwing general Exception so then code will not compile.
      •    In case of checked exception code will not compile
      •    In case of runtimeException code will work fine.

3.    Both base and derived class overridden method throw same exception
       •    Code will compile and run perfectly in both cases of checked and unchecked exception.

4.    Base class overridden method throwing newer/broader exception than derived class overriding method.
       Suppose base class overridden method is throwing general Exception and derived class overriding
       method is throwing ArithmeticException so then code will compile and work fine.
       •     Code will compile and run perfectly in both cases of checked and unchecked exception.

5.    Base class overridden method is throwing exception but Derived class overriding method is not 
       throwing  exception.
      •    Code will compile and run perfectly in both cases of checked and unchecked exception.

How to solve JSF issue view could not be restored

Log Error : - javax.servlet.ServletException: viewId:/mysettings/myinvoiceTemplates/BillingTemplate.html - View /mysettings/myinvoiceTemplates/BillingTemplate.html could not be restored.

Issue : - Sometimes when we open a JSF page in the application and then open some other page in new tab with right clicking on the existing page and work on new opened page for 2 or 3 minute. When we come back to the earlier page after 2 or 3 minutes and click on any button then we get this error in log that page could not be restored.

Solution : -  It can be solved with two ways as below:
1). By default JSF store the state of the page at server side. We can change this to client by changing context parameter “state_saving_method” in web.xml  as:
<context-param>
       <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
       <param-value>client</param-value>
</context-param>

After changing the method to client, the state of the page is saved in a input hidden field at client side with the page. This will solve the above problem.
Advantage :-
Lower the terrific to server because for page state container does not need to go to client side.
Disadvantage : - This can lead to more data download when we open the page because now page state is also stored at client side.

2). Add one more context parameter in Web.xml file. It will re-create/restore the expired view.

<context-param> 

      <param-name>com.sun.faces.enableRestoreView11Compatibility</param-name>   

      <param-value>true</param-value> 

</context-param>

How to close the popup window by pressing escape key button or clicking outside of the popup window with jQuery.

For closing the open popup window on the click of escape key or clciking outside the popup window, We need to create one jQuery method in every modal panel .xhtml file or any other .xhtml file which is used to show the popup window as:

<script type="text/javascript">
    jQuery(document).keyup(function (e){
            var clickedID = e.target.id;
            var unicode=e.keyCode? e.keyCode : e.charCode /*This will capture the key pressed event*/
                 if(unicode==27){//Key code for escape key is 27
                 Richfaces.hideModalPanel(#{modalPanelId});
                /*var win = window.open("","_self"); r
                 win.close();*/
                }
</script>

The above method will automatically be called whenever we press any key and if pressed key is escape key then it would close the opened popup window so it will work when we press theescape key.

To close popup window when we click on the outside of the popup window, we have to call “Richfaces. hideModalPanel(‘modelPanel Id’)” on “onmaskclick”  event of rich:modalPanel as:

onmaskclick="Richfaces.hideModalPanel('#{modalPanelId}')"

How to compile .JRXML file and produce .jasper file with JAVA code

The Jasper Report design file specifies the layout and appearance of the report and they works best with the .JRXML extension files. We use iReport to deal with the jrxml reports but sometimes we need to compile JRXML file through our java code. We can do this with the help of net.sf.jasperreports package.
Change the path of the JRXML and jasper files in below code and run this code to compile any JRXML file and generate jasper report.

import net.sf.jasperreports.engine.JRException;
import net.sf.jasperreports.engine.JasperCompileManager;


public class compileJasper{

public static void main(String[] args)
    {
    //    below code will compile the jasper file which is located on path given below
        try {
    JasperCompileManager.compileReportToFile("PathOfTheJRXMLFile(which needs to be compiled)" ,"PathOfJasperFile(Where to save generated jasper file)");
        } catch (JRException e) {
           
        }
    }
}