装饰者模式（Decorator Pattern）

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

public class LowerCaseInputStream extends FilterInputStream {

    protected LowerCaseInputStream(InputStream in) {
        super(in);
    }
    public int read() throws IOException {
        int c = super.read();
        return c == -1 ? c : Character.toLowerCase((char)c);
    }
    public int read(byte[] b, int offset, int len) throws IOException {
        int result = super.read(b, offset, len);
        for(int i = offset; i < offset + result; i++) {
            b[i] = (byte)Character.toLowerCase((char)b[i]);
        }
        return result;
    }
    
    public static void main(String[] args) {
        int c;
        try {
            InputStream in = new LowerCaseInputStream(new BufferedInputStream(new FileInputStream("test.txt")));
//设置FileInputStream，先用
//BufferedInputStream装饰它，再用我们写的LowerCaseInputStream过滤器装饰它
            while((c = in.read()) >= 0) {
                System.out.print((char)c);
            }
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}