当正则表达式正确时 Java 正则表达式问题

Question

我有一个正确的正则表达式，但在我的程序中失败了。通常，不同的眼光是好的。

相关代码:

String s_mapping = ".*<MAPPING DESCRIPTION.*NAME =.*";
Pattern mapName = Pattern.compile("\"(m_.*?)\"");
String o_mapping = "";

...

if (line.matches(s_mapping)){
                Matcher matcher = mapName.matcher(line);
                System.out.println(line);
                System.out.println(matcher);
                o_mapping = matcher.group(1);
                System.out.println(o_mapping);

输出

<MAPPING DESCRIPTION ="Mapping to generate the parameters file based on the parameters inserted in the table." ISVALID ="YES" NAME ="m_FAR_Gen_ParmFile" OBJECTVERSION ="1" VERSIONNUMBER ="2">
java.util.regex.Matcher[pattern="(m_.*?)" region=0,195 lastmatch=]
Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: No match found

我希望最终看到 m_FAR_Gen_ParmFile 作为我的 o_mapping 输出。

当我在此站点测试时:http://www.regexplanet.com/advanced/java/index.html ，一切都过去了，一切都很好。为什么我的程序会失败？我该如何解决这个问题？

Answer 1

您需要在group()之前调用find():

if (line.matches(s_mapping)){
    Matcher matcher = mapName.matcher(line);
    System.out.println(line);
    System.out.println(matcher);
    matcher.find();
    o_mapping = matcher.group(1);
    System.out.println(o_mapping);

来自Matcher#group() Java文档:

Throws:
IllegalStateException - If no match has yet been attempted, or if the previous match operation failed