在txt文件中的特定位置追加字符串- Java

File file = new File("path/to/file.txt");
FileReader fr = new FileReader(file);

BufferedReader br = new BufferedReader(fr);
String line;
StringBuilder sb = new StringBuilder();

while ((line = br.readLine()) != null) {
    sb.append(line);
    sb.append(System.lineSeparator());
}

br.close();

int lineNumber = 3;
String textToAppend = "This is the appended text.";

String[] lines = sb.toString().split(System.lineSeparator());
lines[lineNumber - 1] += textToAppend;

sb.setLength(0); // 清空StringBuilder对象

for (String updatedLine : lines) {
    sb.append(updatedLine);
    sb.append(System.lineSeparator());
}

FileWriter fw = new FileWriter(file);
fw.write(sb.toString());
fw.close();