Help,I want to change mysql database password

hello ,i am a chinese.
there is a problem,i have installed user application,and use jboss as the application server,use mysql as the database.
now i want to modify mysql's root password.if i change the mysql's root password,the user application cannot connect to mysql database.
Is there a configuration file to store mysql's user name and password. i just modify this configuration file and restart user application so that i don't need to reinstall.
please help me!