使用Apache Commons Lang：

Using Apache Commons Lang:

!StringUtils.isAlphanumeric(String)

对String的字符进行交替迭代，并检查：

Alternativly iterate over String's characters and check with:

!Character.isLetterOrDigit(char)

您还有一个问题：
您的示例字符串abcdefà是字母数字的，因为à是一封信。

You've still one problem left: Your example string "abcdefà" is alphanumeric, since à is a letter. But I think you want it to be considered non-alphanumeric, right?!

因此，您可能想使用正则表达式：

So you may want to use regular expression instead:

String s = "abcdefà";
Pattern p = Pattern.compile("[^a-zA-Z0-9]");
boolean hasSpecialChar = p.matcher(s).find();