RandomAccessFile、FileChannel、MappedByteBuffer读写文件

package com.nio;  
  
import java.io.Closeable;  
import java.io.FileNotFoundException;  
import java.io.IOException;  
import java.io.RandomAccessFile;  
import java.nio.CharBuffer;  
import java.nio.MappedByteBuffer;  
import java.nio.channels.FileChannel;  
import java.nio.channels.FileChannel.MapMode;  
import java.nio.charset.Charset;  
import java.nio.charset.CharsetDecoder;  
import java.nio.charset.CharsetEncoder;  
  
import junit.framework.TestCase;  
  
public class TestNIO extends TestCase {  
    private static final int K = 0x400;  
      
    private static final String FILE_PATH = "c:/nio.txt";  
  
    private void close(Closeable closeable) {  
        if (closeable != null) {  
            try {  
                closeable.close();  
                closeable = null;  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  
  
    public void testWrite() {  
        RandomAccessFile raf = null;  
        FileChannel fc = null;  
        Charset charset = Charset.defaultCharset();  
        CharsetEncoder charsetEncoder = charset.newEncoder();  
  
        try {  
            raf = new RandomAccessFile(FILE_PATH, "rw");  
            fc = raf.getChannel();  
            MappedByteBuffer mbb = fc.map(MapMode.READ_WRITE, 0, K);  
            CharBuffer cb = CharBuffer.wrap("A".toCharArray());  
            charsetEncoder.encode(cb, mbb, true);  
            mbb.flip(); //encode后，mbb的指针不在0的地方，所以要flip  
            fc.position(0);//从头开始写，这行代码可能多余，因为position可能一开始就在0  
            for (int i = 0; i < K; i++) {  
                fc.write(mbb);   
                mbb.flip(); //write后，mbb的指针不在0的地方，所以要flip  
            }  
        } catch (FileNotFoundException e) {  
            e.printStackTrace();  
        } catch (IOException e) {  
            e.printStackTrace();  
        } finally {  
            close(fc);  
            close(raf);  
        }  
    }  
  
    public void testRead() {  
        RandomAccessFile raf = null;  
        FileChannel fc = null;  
        Charset charset = Charset.defaultCharset();  
        CharsetDecoder charsetDecoder = charset.newDecoder();  
        StringBuilder sb = new StringBuilder();  
  
        try {  
            raf = new RandomAccessFile(FILE_PATH, "rw");  
            fc = raf.getChannel();  
            MappedByteBuffer mbb = fc.map(MapMode.READ_WRITE, 0, K);  
            fc.position(0);//从头开始读，这行代码可能多余，因为position可能一开始就在0  
            while (fc.read(mbb) != -1) {  
                mbb.flip();//read后，mbb的指针不在0的地方，所以要flip  
                CharBuffer cb = charsetDecoder.decode(mbb);  
                mbb.flip();//decode后，mbb的指针不在0的地方，所以要flip  
                sb.append(cb);  
            }  
            System.out.println(sb);  
        } catch (FileNotFoundException e) {  
            e.printStackTrace();  
        } catch (IOException e) {  
            e.printStackTrace();  
        } finally {  
            close(fc);  
            close(raf);  
        }  
    }  
      
}