java - 如果模式为空，则打印空值

Question

我有这个 Java 模式匹配代码:

                out.println("<tr>");
                out.println("<td>" + file_path+ "</td>");
                out.println("<td> .sql </td>");

                Pattern pattern = Pattern.compile("(?<key>([\\w]+)?): (?<value>(.+)?)");
                Matcher matcher = pattern.matcher(text);
                while (matcher.find())
                {
                    if (matcher.group("key").equals("author")) {
                        out.println("<td>" + matcher.group("value") + "</td>");
                    } else {
                        out.println("<td> N/A </td>");
                    }
                }
                out.println("<td> date </td>");

如果 matcher.group 或 matcher 中没有找到值，你知道如何打印“N/A ”吗？目前表格单元格已被剪切。

Answer 1

看起来微不足道；设置一个 boolean 值:

out.println("<tr>");
out.println("<td>" + file_path+ "</td>");
out.println("<td> .sql </td>");

Pattern pattern = Pattern.compile("(?<key>([\\w]+)?): (?<value>(.+)?)");
Matcher matcher = pattern.matcher(text);
boolean noMatches = true;
while (matcher.find()) {
  noMatches = false;
  if (matcher.group("key").equals("author")) {
    out.println("<td>" + matcher.group("value") + "</td>");
  } else {
    out.println("<td> N/A </td>");
  }
}
if (noMatches) {
  out.println("<td> N/A </td>");
}
out.println("<td> date </td>");

然后你可以清理它很多:

out.println("<tr>");
out.println("<td>" + file_path+ "</td>");
out.println("<td> .sql </td>");

Pattern pattern = Pattern.compile("author: (.*)");
Matcher matcher = pattern.matcher(text);
if (matcher.find()) {
  out.println("<td>" + matcher.group(1) + "</td>");
} else {
  out.println("<td> N/A </td>");
}
out.println("<td> date </td>");