47、Java正则表达式匹配与替换全解析

Java正则表达式匹配与替换全解析

1. 匹配结果示例

在Java中，我们可以使用正则表达式来识别和提取字符串中的特定信息。下面是一个示例，它展示了如何从URL字符串中识别和报告URL的协议（如 http 或 https ）、主机名和可选的端口号：

String url = "http://regex.info/blog";
String regex = "(?x)^(https?):// ([^/:]+) (?:(\\d+))?";
Matcher m = Pattern.compile(regex).matcher(url);
if (m.find()) {
    System.out.print(
        "Overall [" + m.group() + "]" +
        " (from " + m.start() + " to " + m.end() + ")\n" +
        "Protocol [" + m.group(1) + "]" +
        " (from " + m.start(1) + " to " + m.end(1) + ")\n" +
        "Hostname [" + m.group(2) + "]" +
        " (from " + m.start(2) + " to " + m.end(2) + ")\n"
    );
    if (m.group(3) == null) {
        System.out.println("No port; default of ’80’ is