Having the database field be configured as a binary string is maybe not ideal, but not a problem either.
The problem is however, that you intend to store the password in there directly. Please do not do this, as it will create a major security flaw.
Hashing it as suggested in another answer is better, but still not really good. The problem with that is, that there are so-called rainbow tables which can be used reverse-lookup hashes to their original value.
The minimum you need to do is use a salted hash (https://en.wikipedia.org/wiki/Salt_(cryptography)) or even better, use something like bcrypt or PBKDF2 (see Password Verification with PBKDF2 in Java) to create a secure hash of the user provided password. These hashes will have fixed lengths and can easily be stored as a binary string in your given database field.
When checking the user entry, just perform the same function again and compare that with the database content. Of course, you must use SSL to transfer the password from client to server.