我推荐Junidecode。它不仅可以处理'Ł'和'Ø'，而且还可以很好地从其他字母(如汉语)转录成拉丁字母。

从java.text.Normalizer开始。

string = Normalizer.normalize(string, Normalizer.Form.NFD);
// or Normalizer.Form.NFKD for a more "compatible" deconstruction 

这将从大多数字符中分离所有重音符号。然后，你只需要将每个字符与字母进行比较，并排除那些不是字母的字符。

string = string.replaceAll("[^\\p{ASCII}]", "");

如果你的文本是Unicode，你应该使用这个:

string = string.replaceAll("\\p{M}", "");

对于Unicode， \\P{M}匹配基本字形，\\P{M}(小写)匹配每个重音。

感谢GarretWilson提供的指针和正则表达式.info提供的Unicode指南。

需要注意的是，Normalizer本身不足以删除变音符。例如，下面的代码不会将重音的é替换为不重音的e:

import static java.text.Normalizer.normalize;
import static java.text.Normalizer.Form.*;

public class T {
  public static void main( final String[] args ) {
    final var text = "Brévis";

    System.out.println(
      normalize( text, NFD ) + " " + 
      normalize( text, NFC ) + " " + 
      normalize( text, NFKD ) + " " + 
      normalize( text, NFKC )
    );
  }
}

@virgo47的解决方案非常快，但很接近。接受的答案使用Normalizer和正则表达式。我想知道Normalizer和正则表达式占用了多少时间，因为删除所有非ascii字符可以在没有正则表达式的情况下完成:

import java.text.Normalizer;

public class Strip {
    public static String flattenToAscii(String string) {
        StringBuilder sb = new StringBuilder(string.length());
        string = Normalizer.normalize(string, Normalizer.Form.NFD);
        for (char c : string.toCharArray()) {
            if (c <= '\u007F') sb.append(c);
        }
        return sb.toString();
    }
}

小的额外加速可以通过写入char[]而不调用toCharArray()来获得，尽管我不确定代码清晰度的降低是否值得这样做:

public static String flattenToAscii(String string) {
    char[] out = new char[string.length()];
    string = Normalizer.normalize(string, Normalizer.Form.NFD);
    int j = 0;
    for (int i = 0, n = string.length(); i < n; ++i) {
        char c = string.charAt(i);
        if (c <= '\u007F') out[j++] = c;
    }
    return new String(out);
}

这种变化具有使用Normalizer的正确性和使用表的一些速度方面的优点。在我的机器上，这个答案比公认的答案快4倍，比@virgo47的答案慢6.6倍到7倍(公认的答案比我机器上的@virgo47的答案慢26倍)。

@David Conrad solution is the fastest I tried using the Normalizer, but it does have a bug. It basically strips characters which are not accents, for example Chinese characters and other letters like æ, are all stripped. The characters that we want to strip are non spacing marks, characters which don't take up extra width in the final string. These zero width characters basically end up combined in some other character. If you can see them isolated as a character, for example like this `, my guess is that it's combined with the space character.

public static String flattenToAscii(String string) {
    char[] out = new char[string.length()];
    String norm = Normalizer.normalize(string, Normalizer.Form.NFD);

    int j = 0;
    for (int i = 0, n = norm.length(); i < n; ++i) {
        char c = norm.charAt(i);
        int type = Character.getType(c);

        //Log.d(TAG,""+c);
        //by Ricardo, modified the character check for accents, ref: http://stackoverflow.com/a/5697575/689223
        if (type != Character.NON_SPACING_MARK){
            out[j] = c;
            j++;
        }
    }
    //Log.d(TAG,"normalized string:"+norm+"/"+new String(out));
    return new String(out);
}

一种快速安全的方式

public static String removeDiacritics(String str) {
    if (str == null)
        return null;
    if (str.isEmpty())
        return "";
    
    int len = str.length();
    StringBuilder sb
        = new StringBuilder(len);
    
    //iterate string codepoints
    for (int i = 0; i < len; ) {
        int codePoint = str.codePointAt(i);
        int charCount
            = Character.charCount(codePoint);
        
        if (charCount > 1) {
            for (int j = 0; j < charCount; j++)
                sb.append(str.charAt(i + j));
            i += charCount;
            continue;
        }
        else if (codePoint <= 127) {
            sb.append((char)codePoint);
            i++;
            continue;
        }
        
        sb.append(
            java.text.Normalizer
                .normalize(
                    Character.toString((char)codePoint),
                    java.text.Normalizer.Form.NFD)
                        .charAt(0));
        i++;
    }
    
    return sb.toString();
}

根据语言的不同，这些可能不被认为是重音(改变字母的发音)，而是变音符符号

https://en.wikipedia.org/wiki/Diacritic#Languages_with_letters_containing_diacritics

“波斯尼亚语和克罗地亚语都有符号“č”、“ovic”、“đ”、“š”和“ž”，这些符号被认为是单独的字母，在字典和其他按字母顺序排列单词的语境中都是这样列出的。”

删除它们可能会从本质上改变单词的意思，或者将字母变成完全不同的字母。