Question

我的matcher.groupCount()给了我4但是当我使用matcher.group(0)，...，matcher.group(0)时，它给了我一个错误。

以下是我的代码：

Pattern pattern = Pattern.compile("([0-9]+).([0-9]+).([0-9]+).([0-9]+)");
Matcher matcher1, matcher2;

GeoIP[0][0] = (GeoIP[0][0]).trim();
GeoIP[0][1] = (GeoIP[0][1]).trim();

System.out.println(GeoIP[0][0]);
System.out.println(GeoIP[0][1]);

matcher1 = pattern.matcher(GeoIP[0][0]);
matcher2 = pattern.matcher(GeoIP[0][1]);

System.out.println("matcher1.groupCount() = " + matcher1.groupCount());
System.out.println("matcher2.groupCount() = " + matcher2.groupCount());

System.out.println("matcher1.group(0) = " (matcher1.group(0)).toString());

控制台：

Exception in thread "main" 1.0.0.0
1.0.0.255
matcher1.groupCount() = 4
matcher2.groupCount() = 4

java.lang.IllegalStateException: No match found
    at java.util.regex.Matcher.group(Unknown Source)
    at filename.main(filename.java:linenumber)

行号指向

System.out.println("matcher1.group(0) = " (matcher1.group(0)).toString());

Answer 1

groupCount只是告诉你在正则表达式中定义了多少个组。如果您想要实际访问结果，则必须先执行匹配！

  if (matcher1.find()) {
    System.out.println("matcher1.group(0) = " (matcher1.group(0)).toString());
  } else {
    System.out.println("No match.");
  }

此外.是正则表达式中的特殊字符，您可能需要\\.？

Answer 2

如果我理解正确，您需要访问创建IP地址的四个字节。您可以尝试使用匹配IP地址的正则表达式，然后拆分找到的字符串，而不是使用组。

String GeoIPs = "192.168.1.21, 10.16.254.1, 233.255.255.255";
Pattern pattern = Pattern.compile("\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}");
Matcher matcher;

matcher = pattern.matcher(GeoIPs);

while (matcher.find()) {
    String match = matcher.group();
    String[] ipParts = match.split("\\.");
    for (String part : ipParts) {
        System.out.print(part + "\t");
    }
    System.out.println();
}

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