ヅラッシュ！ by NI-Lab.

import java.util.regex.*;
 
public class RegexSample {
 
  public static void main(String[] args) throws Exception {
 
    String src = "<a href=\"a.html\" id=\"hoge\">Welcome to the Hoge.</a>";
 
    // ?で最短一致(最小一致・最小マッチ)
    Pattern pattern = Pattern.compile("href=\".*?\"");
    Matcher matcher = pattern.matcher(src);
    StringBuffer sb = new StringBuffer();
    while (matcher.find()) {
      String g = matcher.group(); // マッチした文字列部分を取得
      System.out.println(g);
      matcher.appendReplacement(sb, "href=\"b.html\"");
    }
    matcher.appendTail(sb);
    String dst = sb.toString();
 
    System.out.println(src);
    System.out.println(dst);
  }
 
}