java - How can I create a password?

Question

I want to give maybe a million password to some users that should be like:

1. It must have at least 6 characters
2. It must have digits and also letters

Should I use Random here? How?

Answer 1

RandomStringUtils from Apache Commons Lang provide some methods to generate a randomized String, that can be used as password.

---

Here are some examples of 8-characters passwords creation:

// Passwords with only alphabetic characters.
for (int i = 0; i < 8; i++) {
    System.out.println(RandomStringUtils.randomAlphabetic(8));
}
System.out.println("--------");
// Passwords with alphabetic and numeric characters.
for (int i = 0; i < 8; i++) {
    System.out.println(RandomStringUtils.randomAlphanumeric(8));
}

which creates the following result:

zXHzaLdG
oDtlFDdf
bqPbXVfq
tzQUWuxU
qBHBRKQP
uBLwSvnt
gzBcTnIm
yTUgXlCc
--------
khDzEFD2
cHz1p6yJ
3loXcBau
F6NJAQr7
PyfN079I
8tJye7bu
phfwpY6y
62q27YRt

Of course, you have also methods that may restrict the set of characters allowed for the password generation:

for (int i = 0; i < 8; i++) {
    System.out.println(RandomStringUtils.random(8, "abcDEF123"));
}

will create only passwords with the characters a, b, c, D, E, F, 1, 2 or 3:

D13DD1Eb
cac1Dac2
FE1bD2DE
2ab3Fb3D
213cFEFD
3c2FEDDF
FDbFcc1E
b2cD1c11