关于算法：如何有效地在Java中生成安全的随机字母数字字符串？

How to generate a secure random alphanumeric string in Java efficiently?

如何高效地生成Java中的安全随机(或伪随机)字母数字串？

初始化一个包含所有可接受字符的数组(CHARS_ARRAY)，然后实例化一个secureRandom实例，并反复调用nextInt(CHARS_ARRAY.length)以获取char数组中的随机索引。将每个字符附加到StringBuilder中，直到得到预期的字符数。

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这是我的代码在重复问题中的一个稍微修改过的版本。

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public final class RandomString
{

/* Assign a string that contains the set of characters you allow. */
private static final String symbols ="ABCDEFGJKLMNPRSTUVWXYZ0123456789";

private final Random random = new SecureRandom();

private final char[] buf;

public RandomString(int length)
{
if (length < 1)
throw new IllegalArgumentException("length < 1:" + length);
buf = new char[length];
}

public String nextString()
{
for (int idx = 0; idx < buf.length; ++idx)
buf[idx] = symbols.charAt(random.nextInt(symbols.length()));
return new String(buf);
}

}

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使用UUID:

1 2	UUID random = UUID.randomUUID(); System.out.println( random );

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import java.security.SecureRandom;
import java.util.Random;

public class PasswordHelper {

public static String generatePassword (int length) {

//minimum length of 6
if (length < 4) {
length = 6;
}

final char[] allAllowed ="abcdefghijklmnopqrstuvwxyzABCDEFGJKLMNPRSTUVWXYZ0123456789".toCharArray();

//Use cryptographically secure random number generator
Random random = new SecureRandom();

StringBuilder password = new StringBuilder();

for (int i = 0; i < length; i++) {
password.append(allAllowed[random.nextInt(allAllowed.length)]);
}

return password.toString();

}

}

。

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String chrs ="0123456789abcdefghijklmnopqrstuvwxyz-_ABCDEFGHIJKLMNOPQRSTUVWXYZ";
SecureRandom secureRandom = SecureRandom.getInstanceStrong();
// 9 is the length of the string you want
String customTag = secureRandom.ints(9, 0, chrs.length()).mapToObj(i -> chrs.charAt(i))
.collect(StringBuilder::new, StringBuilder::append, StringBuilder::append).toString();
System.out.println(customTag);

。

示例：

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// q3HX6EctP
// WjRrMjQT4
// sX-Piq4DB

为开放密钥加密算法生成公钥，并通过base64算法将字节序列转换为字符串。

http://download.oracle.com/javase/6/docs/api/java/security/securelrandom.html下载

来自JavaDoc：

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SecureRandom random = new SecureRandom();
byte bytes[] = new byte[20];
random.nextBytes(bytes);

号

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