我开发了一个应用程序，为我的项目开发一个自动生成的字母数字字符串。在这个字符串中，前三个字符是字母，后七个字符是整数。

public class AlphaNumericGenerator {

    public static void main(String[] args) {
        java.util.Random r = new java.util.Random();
        int i = 1, n = 0;
        char c;
        String str = "";
        for (int t = 0; t < 3; t++) {
            while (true) {
                i = r.nextInt(10);
                if (i > 5 && i < 10) {

                    if (i == 9) {
                        i = 90;
                        n = 90;
                        break;
                    }
                    if (i != 90) {
                        n = i * 10 + r.nextInt(10);
                        while (n < 65) {
                            n = i * 10 + r.nextInt(10);
                        }
                    }
                    break;
                }
            }
            c = (char)n;

            str = String.valueOf(c) + str;
        }

        while(true){
            i = r.nextInt(10000000);
            if(i > 999999)
                break;
        }
        str = str + i;
        System.out.println(str);
    }
}

在前面的答案中有很多StringBuilder的用法。我想这很简单，但它需要每个字符调用一个函数，增加一个数组，等等。。。

如果使用字符串生成器，建议指定字符串所需的容量，即。，

new StringBuilder(int capacity);

这是一个不使用StringBuilder或字符串附加的版本，也没有字典。

public static String randomString(int length)
{
    SecureRandom random = new SecureRandom();
    char[] chars = new char[length];
    for(int i=0; i<chars.length; i++)
    {
        int v = random.nextInt(10 + 26 + 26);
        char c;
        if (v < 10)
        {
            c = (char)('0' + v);
        }
        else if (v < 36)
        {
            c = (char)('a' - 10 + v);
        }
        else
        {
            c = (char)('A' - 36 + v);
        }
        chars[i] = c;
    }
    return new String(chars);
}

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);
}

我正在使用Apache Commons的库生成一个字母数字字符串：

import org.apache.commons.lang3.RandomStringUtils;

String keyLength = 20;
RandomStringUtils.randomAlphanumeric(keylength);

它又快又简单！

最佳随机字符串生成器方法

public class RandomStringGenerator{

    private static int randomStringLength = 25 ;
    private static boolean allowSpecialCharacters = true ;
    private static String specialCharacters = "!@$%*-_+:";
    private static boolean allowDuplicates = false ;

    private static boolean isAlphanum = false;
    private static boolean isNumeric = false;
    private static boolean isAlpha = false;
    private static final String alphabet = "abcdefghijklmnopqrstuvwxyz";
    private static boolean mixCase = false;
    private static final String capAlpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static final String num = "0123456789";

    public static String getRandomString() {
        String returnVal = "";
        int specialCharactersCount = 0;
        int maxspecialCharacters = randomStringLength/4;

        try {
            StringBuffer values = buildList();
            for (int inx = 0; inx < randomStringLength; inx++) {
                int selChar = (int) (Math.random() * (values.length() - 1));
                if (allowSpecialCharacters)
                {
                    if (specialCharacters.indexOf("" + values.charAt(selChar)) > -1)
                    {
                        specialCharactersCount ++;
                        if (specialCharactersCount > maxspecialCharacters)
                        {
                            while (specialCharacters.indexOf("" + values.charAt(selChar)) != -1)
                            {
                                selChar = (int) (Math.random() * (values.length() - 1));
                            }
                        }
                    }
                }
                returnVal += values.charAt(selChar);
                if (!allowDuplicates) {
                    values.deleteCharAt(selChar);
                }
            }
        } catch (Exception e) {
            returnVal = "Error While Processing Values";
        }
        return returnVal;
    }

    private static StringBuffer buildList() {
        StringBuffer list = new StringBuffer(0);
        if (isNumeric || isAlphanum) {
            list.append(num);
        }
        if (isAlpha || isAlphanum) {
            list.append(alphabet);
            if (mixCase) {
                list.append(capAlpha);
            }
        }
        if (allowSpecialCharacters)
        {
            list.append(specialCharacters);
        }
        int currLen = list.length();
        String returnVal = "";
        for (int inx = 0; inx < currLen; inx++) {
            int selChar = (int) (Math.random() * (list.length() - 1));
            returnVal += list.charAt(selChar);
            list.deleteCharAt(selChar);
        }
        list = new StringBuffer(returnVal);
        return list;
    }   

}

给定一些字符（AllCharacters），您可以随机选择字符串中的一个字符。然后使用for循环重复获取随机字符。

public class MyProgram {
  static String getRandomString(int size) {
      String AllCharacters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
      StringBuilder sb = new StringBuilder(size);
      int length = AllCharacters.length();
      for (int i = 0; i < size; i++) {
          sb.append(AllCharacters.charAt((int)(length * Math.random())));
      }
      return sb.toString();
  }

  public static void main(String[] args) {
      System.out.println(MyProgram.getRandomString(30));
  }
}

在沙盒上试试另请参阅其他语言实现随机字符串生成器