Java如何使用固定字节数读取文件呢?

     使用 FileInputStream 读取文件
          使用FileWriter写入文件

public class TestClass{
    public static void main(String[] args){

    byte[] buffer = new byte[100];

    try{
        FileInputStream f = new FileInputStream("test.txt");
        FileWriter writer = new FileWriter("copy_test.txt");
        int b;
        while ((b=f.read(buffer)) != -1 )
            writer.write(new String(buffer));
        writer.close();
    } catch(Exception e){
        e.printStackTrace();
    }
 }
}