Null check function in Javascript.

function checkNullField()

{

var field1 = document.formName.fieldName.value;

if(field1 == '')

{

alert("Field Name is empty");

return false;

}

else

{

return true;

}

}

Once you call this function in your jsp as return checkNullField(); then this function will return false if the field is empty else it will return true.