JAVA replaceAll regex和replacement转义

女爷i 2022-05-26 12:42 193阅读 0赞

# JAVA replaceAll regex和replacement转义 #

*  JAVA replaceAll regex和replacement转义
    
     *  replacement转义
     *  regex转义

## replacement转义 ##

有下面这段代码：

public static void main(String[] args){
        System.out.println("abcdef".replaceAll("abc","$"));//1
        System.out.println("abcdef".replaceAll("abc", "\\"));//2
    }

咋一看没毛病，但是运行会报错：

1:Exception in thread "main" java.lang.IllegalArgumentException: Illegal group reference: group index is missing
    2:Exception in thread "main" java.lang.IllegalArgumentException: character to be escaped is missing

因为`\`和`$`是`replacement`中的特殊字符，前者用来转义，后者用来匹配组并使用`$n`来引用第`n`个组。它们的正确使用方法如下：

System.out.println("abcdef".replaceAll("abc", "\\\\"));// \def
    System.out.println("abcdef".replaceAll("abc", "\\$"));// $def
    System.out.println("www.baidu.com".replaceAll("(.*)\\.(baidu)\\.(.*)", "https://$1.google.$3"));// https://www.google.com

可以看出这两个特殊字符的作用了，所以如果`replacement`里面包含有这两个特殊字符，却没有按照需要的规则来匹配，就会报错。除了直接使用`\`转义以外，还有一种方法在不知道`replacement`中是否包含特殊字符是特别有用：

public static void main(String[] args){
        System.out.println(replaceAll("abcdef","abc", "\\"));
        System.out.println(replaceAll("abcdef","abc", "$"));
    }
    
    public static String replaceAll(String s,String regex,String replacement){
        return s.replaceAll(regex,Matcher.quoteReplacement(replacement));
    }

使用`Matcher.quoteReplacement(replacement)`就能将`replacement`中的所有特殊字符转义，是一种非常保险的方法，`Matcher.quoteReplacement()`就是一个转义的操作：

/** * Returns a literal replacement <code>String</code> for the specified * <code>String</code>. * * This method produces a <code>String</code> that will work * as a literal replacement <code>s</code> in the * <code>appendReplacement</code> method of the {@link Matcher} class. * The <code>String</code> produced will match the sequence of characters * in <code>s</code> treated as a literal sequence. Slashes ('\') and * dollar signs ('$') will be given no special meaning. * * @param s The string to be literalized * @return A literal string replacement * @since 1.5 */
    public static String quoteReplacement(String s) {
        if ((s.indexOf('\\') == -1) && (s.indexOf('$') == -1))
            return s;
        StringBuilder sb = new StringBuilder();
        for (int i=0; i<s.length(); i++) {
            char c = s.charAt(i);
            if (c == '\\' || c == '$') {
                sb.append('\\');
            }
            sb.append(c);
        }
        return sb.toString();
    }

## regex转义 ##

和`replacement`类似的，如果`regex`中有字符需要转义，也可主动加`\`来转义，但是在不确定`regex`中是否有特殊字符时，可能就会出错：

public static void main(String[] args){
        System.out.println(replaceAll("My name is ${name}","${name}", "Hanmeimei"));
    }
    
    public static String replaceAll(String s,String regex,String replacement){
        return s.replaceAll(regex,Matcher.quoteReplacement(replacement));
    }

Exception in thread "main" java.util.regex.PatternSyntaxException: Illegal repetition near index 0
    ${name}
    ^

在确定`regex`中不包含正则表达式的时候，可以使用`Pattern.quote()`来转义：

public static void main(String[] args){
        System.out.println(replaceAll("My name is ${name}","${name}", "Hanmeimei"));//My name is Hanmeimei
    }
    
    public static String replaceAll(String s,String regex,String replacement){
        return s.replaceAll(Pattern.quote(regex),Matcher.quoteReplacement(replacement));
    }