我在用着Pattern/Matcher获取 HTTP 响应中的响应代码。groupCount返回 1，但在尝试获取它时出现异常！知道为什么吗？
这是代码：
//get response code
String firstHeader = reader.readLine();
Pattern responseCodePattern = Pattern.compile("^HTTP/1\\.1 (\\d+) OK$");
System.out.println(firstHeader);
System.out.println(responseCodePattern.matcher(firstHeader).matches());
System.out.println(responseCodePattern.matcher(firstHeader).groupCount());
System.out.println(responseCodePattern.matcher(firstHeader).group(0));
System.out.println(responseCodePattern.matcher(firstHeader).group(1));
responseCode = Integer.parseInt(responseCodePattern.matcher(firstHeader).group(1));
这是输出：
HTTP/1.1 200 OK
true
1
Exception in thread "Thread-0" java.lang.IllegalStateException: No match found
at java.util.regex.Matcher.group(Unknown Source)
at cs236369.proxy.Response.<init>(Response.java:27)
at cs236369.proxy.ProxyServer.start(ProxyServer.java:71)
at tests.Hw3Tests$1.run(Hw3Tests.java:29)
at java.lang.Thread.run(Unknown Source)
pattern.matcher(input)总是创建一个新的匹配器，所以你需要调用matches() again.
Try:
Matcher m = responseCodePattern.matcher(firstHeader);
m.matches();
m.groupCount();
m.group(0); //must call matches() first
...
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