public static String randomSeriesForThreeCharacter() {
    Random r = new Random();
    String value = "";
    char random_Char ;
    for(int i=0; i<10; i++)
    {
        random_Char = (char) (48 + r.nextInt(74));
        value = value + random_char;
    }
    return value;
}

使用美元应简单如下：

// "0123456789" + "ABCDE...Z"
String validCharacters = $('0', '9').join() + $('A', 'Z').join();

String randomString(int length) {
    return $(validCharacters).shuffle().slice(length).toString();
}

@Test
public void buildFiveRandomStrings() {
    for (int i : $(5)) {
        System.out.println(randomString(12));
    }
}

它输出的内容如下：

DKL1SBH9UJWC
JH7P0IT21EA5
5DTI72EO6SFU
HQUMJTEBNF7Y
1HCR6SKYWGT7

public static String generateSessionKey(int length){
    String alphabet =
        new String("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"); // 9

    int n = alphabet.length(); // 10

    String result = new String();
    Random r = new Random(); // 11

    for (int i=0; i<length; i++) // 12
        result = result + alphabet.charAt(r.nextInt(n)); //13

    return result;
}

您可以创建一个包含所有字母和数字的字符数组，然后可以从该字符数组中随机选择并创建自己的字符串密码。

char[] chars = new char[62]; // Sum of letters and numbers

int i = 0;

for(char c = 'a'; c <= 'z'; c++) { // For letters
    chars[i++] = c;
}

for(char c = '0'; c <= '9';c++) { // For numbers
    chars[i++] = c;
}

for(char c = 'A'; c <= 'Z';c++) { // For capital letters
    chars[i++] = c;
}

int numberOfCodes = 0;
String code = "";
while (numberOfCodes < 1) { // Enter how much you want to generate at one time
    int numChars = 8; // Enter how many digits you want in your password

    for(i = 0; i < numChars; i++) {
        char c = chars[(int)(Math.random() * chars.length)];
        code = code + c;
    }
    System.out.println("Code is:" + code);
}

这里是一个基于流的Java8解决方案。

    public String generateString(String alphabet, int length) {
        return generateString(alphabet, length, new SecureRandom()::nextInt);
    }

    // nextInt = bound -> n in [0, bound)
    public String generateString(String source, int length, IntFunction<Integer> nextInt) {
        StringBuilder sb = new StringBuilder();
        IntStream.generate(source::length)
                .boxed()
                .limit(length)
                .map(nextInt::apply)
                .map(source::charAt)
                .forEach(sb::append);

        return sb.toString();
    }

像这样使用

String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
int length = 12;
String generated = generateString(alphabet, length);
System.out.println(generated);

函数nextInt应该接受一个int绑定，并返回一个介于0和绑定-1之间的随机数。

Java 8中的另一种选择是：

static final Random random = new Random(); // Or SecureRandom
static final int startChar = (int) '!';
static final int endChar = (int) '~';

static String randomString(final int maxLength) {
  final int length = random.nextInt(maxLength + 1);
  return random.ints(length, startChar, endChar + 1)
        .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
        .toString();
}