java read需要import

java.io.InputStream 和java.io.InputStreamReader类，具体代码如下：

import java.io.*;

public class Main {
    public static void main(String[] args) {
        try {
            InputStream is = new FileInputStream("file.txt");
            InputStreamReader isr = new InputStreamReader(is);
            
            int c;
            while ((c = isr.read()) != -1) {
                System.out.print((char)c);
            }
            
            isr.close();
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}