Java 调用 replaceAll()方法报错:java.lang.IllegalArgumentException: Illegal group reference等错误

偏执的太偏执、 2022-03-06 09:34 1849阅读 0赞

Java 调用 replaceAll()方法报错:java.lang.IllegalArgumentException: character to be escaped is missing、Illegal group reference: group index is missing、named capturing group has 0 length name、named capturing group is missing trailing ‘\}’、Illegal group reference等。

例如运行一下代码:

public static void main(String[] args) {
            String regex = "str";
            String replacement = "a$bc$d";
            String str = "test str replace.";
            String str1 = str.replaceAll(regex, replacement);
            System.out.println(str1);
        }

会抛出以下错误：

![qw][]

String的replaceAll(regex, replacement)方法会调用java.util.regex.Matcher.appendReplacement(sb, replacement)方法，appendReplacement(sb, replacement)方法的源码如下：

public Matcher appendReplacement(StringBuffer sb, String replacement) {
    
            // If no match, return error
            if (first < 0)
                throw new IllegalStateException("No match available");
    
            // Process substitution string to replace group references with groups
            int cursor = 0;
            StringBuilder result = new StringBuilder();
    
            while (cursor < replacement.length()) {
                char nextChar = replacement.charAt(cursor);
                if (nextChar == '\\') {
                    cursor++;
                    if (cursor == replacement.length())
                        throw new IllegalArgumentException(
                            "character to be escaped is missing");
                    nextChar = replacement.charAt(cursor);
                    result.append(nextChar);
                    cursor++;
                } else if (nextChar == '$') {
                    // Skip past $
                    cursor++;
                    // Throw IAE if this "$" is the last character in replacement
                    if (cursor == replacement.length())
                       throw new IllegalArgumentException(
                            "Illegal group reference: group index is missing");
                    nextChar = replacement.charAt(cursor);
                    int refNum = -1;
                    if (nextChar == '{') {
                        cursor++;
                        StringBuilder gsb = new StringBuilder();
                        while (cursor < replacement.length()) {
                            nextChar = replacement.charAt(cursor);
                            if (ASCII.isLower(nextChar) ||
                                ASCII.isUpper(nextChar) ||
                                ASCII.isDigit(nextChar)) {
                                gsb.append(nextChar);
                                cursor++;
                            } else {
                                break;
                            }
                        }
                        if (gsb.length() == 0)
                            throw new IllegalArgumentException(
                                "named capturing group has 0 length name");
                        if (nextChar != '}')
                            throw new IllegalArgumentException(
                                "named capturing group is missing trailing '}'");
                        String gname = gsb.toString();
                        if (ASCII.isDigit(gname.charAt(0)))
                            throw new IllegalArgumentException(
                                "capturing group name {" + gname +
                                "} starts with digit character");
                        if (!parentPattern.namedGroups().containsKey(gname))
                            throw new IllegalArgumentException(
                                "No group with name {" + gname + "}");
                        refNum = parentPattern.namedGroups().get(gname);
                        cursor++;
                    } else {
                        // The first number is always a group
                        refNum = (int)nextChar - '0';
                        if ((refNum < 0)||(refNum > 9))
                            throw new IllegalArgumentException(
                                "Illegal group reference");
                        cursor++;
                        // Capture the largest legal group string
                        boolean done = false;
                        while (!done) {
                            if (cursor >= replacement.length()) {
                                break;
                            }
                            int nextDigit = replacement.charAt(cursor) - '0';
                            if ((nextDigit < 0)||(nextDigit > 9)) { // not a number
                                break;
                            }
                            int newRefNum = (refNum * 10) + nextDigit;
                            if (groupCount() < newRefNum) {
                                done = true;
                            } else {
                                refNum = newRefNum;
                                cursor++;
                            }
                        }
                    }
                    // Append group
                    if (start(refNum) != -1 && end(refNum) != -1)
                        result.append(text, start(refNum), end(refNum));
                } else {
                    result.append(nextChar);
                    cursor++;
                }
            }
            // Append the intervening text
            sb.append(text, lastAppendPosition, first);
            // Append the match substitution
            sb.append(result);
    
            lastAppendPosition = last;
            return this;
        }

可以看到这里面对“$”符号和"\\\\"符号进行了处理。出现以上错误的原因是：String的replaceAll(regex, replacement)方法的第一个参数支持正则表达式，如果参数replacement中出现符号“$”,会按照$1$2的分组模式进行匹配。当编译器发现“$”后跟的不是整数的时候，就会抛出“Illegal group reference”的异常。

处理办法：用JDK提供的方法，对特殊字符进行处理：

replacement = java.util.regex.Matcher.quoteReplacement(replacement);

该方法把符号"$“与符号”\\\\“添加了”\\\\"进行转义，前面的代码可以写成以下：

public static void main(String[] args) {
            String regex = "str";
            String replacement = "a$bc$d";
            replacement = java.util.regex.Matcher.quoteReplacement(replacement);
            String str = "test str replace.";
            String str1 = str.replaceAll(regex, replacement);
            System.out.println(str1);
        }

[qw]: /images/20220303/464ca277789c43cdbc49560135b0f893.png