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Custom Exception

  Asked By: Adelisa    Date: Oct 18    Category: Java    Views: 1264
  

Can anybody help in creating custom exceptions in
servlets and jsp..

I want create my own Exception Which can be put in a
try catch block and caught from servlets, jsp , java
beans etc..

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1 Answer Found

 
Answer #1    Answered By: Benjamin Simpson     Answered On: Oct 18

ur project may have different layer. it is a good idea to have a layered exception  handling. define ur own exception class for every layer. they all should extend a parent exception which extends Exception.java.

in every layer u should catch  the lower layer exception and throw the exception of this layer.
u may have different types of exception constructors . this depends on what u want to do, what u want to throw and what u want to show.

as an example for service layer u can have this :


public class ServiceException extends ParentException
{
/**
* @deprecated dont use this
* @param errMsg
*/
public ServiceException(String errMsg)
{
this.setErrorMessage(errMsg);
}

/**
* @deprecated dont use this
* @param e
*/
public ServiceException(Throwable e)
{
this.setThrowable(e);
}

/**
* @deprecated dont use this
* @param errorNumber
* @param errMsg
* @param e
*/
public ServiceException(int errorNumber,String errMsg, Throwable e)
{
this.setErrorNumber(errorNumber);
this.setErrorMessage(errMsg);
this.setThrowable(e);
}

public ServiceException(int errorNumber,String errMsg)
{
this.setErrorNumber(errorNumber);
this.setErrorMessage(errMsg);
}

}



parent class is as follows:

public class ParentException extends java.lang.Exception
{
private String errorMessage = null;
private int errorNumber = 0;
private Throwable throwable = null;

public ParentException()
{
printStackTrace();
}

public void setErrorMessage(String errorMessage)
{
this.errorMessage = errorMessage;
}

public String getErrorMessage()
{
return errorMessage;
}

public void setErrorNumber(int errorNumber)
{
this.errorNumber = errorNumber;
}

public int getErrorNumber()
{
return errorNumber;
}

public ParentException(int errNumber,String errMsg,Throwable throwable)
{
this.errorMessage = errMsg;
this.errorNumber = errNumber;
this.throwable = throwable;
}
public ParentException(int errNumber,String errMsg)
{
this.errorMessage = errMsg;
this.errorNumber = errNumber;
}
public void setThrowable(Throwable throwable)
{
this.throwable = throwable;
}

public Throwable getThrowable()
{
return throwable;
}
}

a method in ur service layer can look like this :


public void myMethod(){
try{
//some operation
}
catch(the_lower_layer_exception_class x){
throw new ServiceException(x);
}
}

it is a long story how to show exception in a jsp. read some books for it. if u use web frameworks like struts, they have some easy ways to do that.

 
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