从文件java读取后替换字符串中的字符

Question

所以我正在编写一个程序，该程序将从文件中读取输入，将所有 html 标记替换为 >、大于和

public void rewrite(String from, String to) {
    File f = new File(from);
    File t = new File(to);
    try {
        Scanner s = new Scanner(f);
        FileWriter fw = new FileWriter(to);
        while (true) {
            if (s.hasNext()) {
                String a = s.next();
                if (a.contains("<") || a.contains(">") || a.contains("&")) {
                    a.replace("<", "&lt;,");
                    a.replace(">","&gt;,");
                    a.replace("&","amp;,");

                }
                fw.append(a);
            } else {
                break;
            }
        }
        fw.close();
        s.close();
    } catch (Exception e) {
        System.out.println(e);
    }
}

编辑：It is a warning not a compile time error nor a runtime error

Answer 1

警告是因为字符串不变性。

你应该使用

a = a.replace("<", "&lt;,");
a = a.replace(">","&gt;,");
a = a.replace("&","amp;,");

否则，被替换的字符串会丢失，原字符串不会被修改。