I had faced same problem. I'm sharing here what I had done then.
Plz check the below things to identify the problem.
1. Check ur internet connection.
2. Check ur DB connection parameters settings in Talend job.
3.Check whether the user which u r using to run this job has the permissions from admin to access the respective DB.
Hope it is helpful to u.
The technical article http://stackoverflow.com/questions/2983248/com-mysql-jdbc-exceptions-jdbc4-communicationsexception-c... about the error("com.mysql.jdbc.exceptions.jdbc4.Communications Exception : Communications link) will point a light to you.
It's a permissions problem. Check the access permissions in the MySQL admin.
The Issue has Been solved as the localhost was blocked from network settings in talend in general tab.