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