Monday, August 24, 2015

aspect in spring


Aspect is modulerization of a concern that cuts accross multiple classes . Take an example of exception handling ,consider exception handling as an Aspect . In a program if an exception occurs it is an example join point as per spring nomenclature . At a join point action taken by Aspect is called an Advice , so if an ExceptionHandlingAspect calls logException(Exception e) ,logException is an example of advice . All advices has a pointcut expression , if for a join point , point cut expression is true , then the advice is executed at the join point .

Sorting list contents

List content is sorted using Collections.sort(listObject,comparatorObject);
For example if have list of Student object and you want to sort it, then you need to create a new object of type Comparator. The logic of comparision is written in

int compare(Object object1,Object object2)

While overriding compare method you need to return the following :
Positive integer : if object 1 > object 2
Negative integer : if object 2> object 1
Zero : if object 1 = object 2

This logic will allow your list to be sorted in ascending order.

Tuesday, May 5, 2015

Public key private key certificate

public key is the one which is shared , l can share my public key to you . Suppose you want to send a document to me .So you can encrypt it using a public key . Once it reaches me I can decrypt it using a private key . If the document is delivered to an unknown person he cannot decrypt it since he does not have the private key .

Sunday, April 26, 2015

Javax.mail.MessagingException

IOException while sending message;
nested exception is:
com.sun.mail.SMTP.SMTPTransport.sendMessage.

You seem to have call javax.mail.Transport. send from a j2ee application.

occurs if attachment is not present.
Remember extension is must , in case the extension is missing you will get this exception .

Monday, April 6, 2015

ec2-user@ec2 Permission denied