使用BufferedWriter写入越来越慢，求解？

Question

1.从大量文件中提取特征信息（已写好），写入到一个txt目标文件中时，发现前1000个文件写入速度比较快，后来越来越慢，问题出在哪里？
2.我使用的写入方法

public static void writeText(File file, String content) {
    BufferedWriter writer = null;
    try {
        writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file, true), "UTF-8"));
        writer.append(content);
        writer.newLine();
        writer.flush();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        if (writer != null) {
            try {
                writer.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}