添加随机工具类。

src/main/java/xyz/zhouxy/plusone/commons/util/RandomUtil.java

@@ -0,0 +1,18 @@
+package xyz.zhouxy.plusone.commons.util;
+
+import java.security.SecureRandom;
+
+public final class RandomUtil {
+    private RandomUtil() {
+        throw new IllegalStateException("Utility class");
+    }
+
+    public static String secureRandomStr(char[] sourceCharacters, int length) {
+        SecureRandom random = new SecureRandom();
+        char[] result = new char[length];
+        for (int i = 0; i < length; i++) {
+            result[i] = sourceCharacters[random.nextInt(sourceCharacters.length)];
+        }
+        return String.valueOf(result);
+    }
+}