通过扩展RandomAccessFile类使之具备Buffer改善I/O性能载

public class RandomAccessFile implements DataOutput, DataInput {
	public final byte readByte() throws IOException {
		int ch = this.read();
		if (ch < 0)
			throw new EOFException();
		return (byte)(ch);
	}
	public native int read() throws IOException; 
	public final void writeByte(int v) throws IOException {
		write(v);
	} 
	public native void write(int b) throws IOException; 
}

public class BufferedInputStream extends FilterInputStream {
	private static int defaultBufferSize = 2048; 
	protected byte buf[]; // 建立读缓存区
	public BufferedInputStream(InputStream in, int size) {
		super(in);        
		if (size <= 0) {
			throw new IllegalArgumentException("Buffer size <= 0");
		}
		buf = new byte[size];
	}
	public synchronized int read() throws IOException {
		ensureOpen();
		if (pos >= count) {
			fill();
			if (pos >= count)
				return -1;
		}
		return buf[pos++] & 0xff; // 直接从BUF[]中读取
	} 
	private void fill() throws IOException {
	if (markpos < 0)
	    pos = 0;		/* no mark: throw away the buffer */
	else if (pos >= buf.length)	/* no room left in buffer */
	    if (markpos > 0) {	/* can throw away early part of the buffer */
		int sz = pos - markpos;
		System.arraycopy(buf, markpos, buf, 0, sz);
		pos = sz;
		markpos = 0;
	    } else if (buf.length >= marklimit) {
		markpos = -1;	/* buffer got too big, invalidate mark */
		pos = 0;	/* drop buffer contents */
	    } else {		/* grow buffer */
		int nsz = pos * 2;
		if (nsz > marklimit)
		    nsz = marklimit;
		byte nbuf[] = new byte[nsz];
		System.arraycopy(buf, 0, nbuf, 0, pos);
		buf = nbuf;
	    }
	count = pos;
	int n = in.read(buf, pos, buf.length - pos);
	if (n > 0)
	    count = n + pos;
	}
}

public class BufferedOutputStream extends FilterOutputStream {
   protected byte buf[]; // 建立写缓存区
   public BufferedOutputStream(OutputStream out, int size) {
		super(out);
		if (size <= 0) {
			throw new IllegalArgumentException("Buffer size <= 0");
		}
		buf = new byte[size];
    } 
public synchronized void write(int b) throws IOException {
		if (count >= buf.length) {
	   		flushBuffer();
		}
		buf[count++] = (byte)b; // 直接从BUF[]中读取
   }
   private void flushBuffer() throws IOException {
		if (count > 0) {
			out.write(buf, 0, count);
			count = 0;
		}
   }
}

public class BufferedRandomAccessFile extends RandomAccessFile {
//  byte read(long pos)：读取当前文件POS位置所在的字节
//  bufstartpos、bufendpos代表BUF映射在当前文件的首/尾偏移地址。
//  curpos指当前类文件指针的偏移地址。
    public byte read(long pos) throws IOException {
        if (pos < this.bufstartpos || pos > this.bufendpos ) {
            this.flushbuf();
            this.seek(pos);
            if ((pos < this.bufstartpos) || (pos > this.bufendpos)) 
                throw new IOException();
        }
        this.curpos = pos;
        return this.buf[(int)(pos - this.bufstartpos)];
    }
// void flushbuf()：bufdirty为真，把buf[]中尚未写入磁盘的数据，写入磁盘。
    private void flushbuf() throws IOException {
        if (this.bufdirty == true) {
            if (super.getFilePointer() != this.bufstartpos) {
                super.seek(this.bufstartpos);
            }
            super.write(this.buf, 0, this.bufusedsize);
            this.bufdirty = false;
        }
    }
// void seek(long pos)：移动文件指针到pos位置，并把buf[]映射填充至POS
所在的文件块。
    public void seek(long pos) throws IOException {
        if ((pos < this.bufstartpos) || (pos > this.bufendpos)) { // seek pos not in buf
            this.flushbuf();
            if ((pos >= 0) && (pos <= this.fileendpos) && (this.fileendpos != 0)) 
{   // seek pos in file (file length > 0)
            	  this.bufstartpos =  pos * bufbitlen / bufbitlen;
                this.bufusedsize = this.fillbuf();
            } else if (((pos == 0) && (this.fileendpos == 0)) 
|| (pos == this.fileendpos + 1)) 
{   // seek pos is append pos
                this.bufstartpos = pos;
                this.bufusedsize = 0;
            }
            this.bufendpos = this.bufstartpos + this.bufsize - 1;
        }
        this.curpos = pos;
    }
// int fillbuf()：根据bufstartpos，填充buf[]。
    private int fillbuf() throws IOException {
        super.seek(this.bufstartpos);
        this.bufdirty = false;
        return super.read(this.buf);
    }
}

// boolean write(byte bw, long pos)：向当前文件POS位置写入字节BW。
// 根据POS的不同及BUF的位置：存在修改、追加、BUF中、BUF外等情
况。在逻辑判断时，把最可能出现的情况，最先判断，这样可提高速度。
// fileendpos：指示当前文件的尾偏移地址，主要考虑到追加因素
    public boolean write(byte bw, long pos) throws IOException {
        if ((pos >= this.bufstartpos) && (pos <= this.bufendpos)) { 
// write pos in buf
            this.buf[(int)(pos - this.bufstartpos)] = bw;
            this.bufdirty = true;
            if (pos == this.fileendpos + 1) { // write pos is append pos
                this.fileendpos++;
                this.bufusedsize++;
            }
        } else { // write pos not in buf
            this.seek(pos);
            if ((pos >= 0) && (pos <= this.fileendpos) && (this.fileendpos != 0)) 
{ // write pos is modify file
                this.buf[(int)(pos - this.bufstartpos)] = bw;
            } else if (((pos == 0) && (this.fileendpos == 0)) 
|| (pos == this.fileendpos + 1)) { // write pos is append pos
                this.buf[0] = bw;
                this.fileendpos++;
                this.bufusedsize = 1;
            } else {
                throw new IndexOutOfBoundsException();
            }
            this.bufdirty = true;
        }
        this.curpos = pos;
        return true;
    }

   public void seek(long pos) throws IOException {
		...
this.bufstartpos =  pos * bufbitlen / bufbitlen; 
// bufbitlen指buf[]的位长，例：若bufsize=1024，则bufbitlen=10。
...
}

    public boolean append(byte bw) throws IOException {
        return this.write(bw, this.fileendpos + 1);
    }

    public boolean write(byte bw) throws IOException {
        return this.write(bw, this.curpos);
    }

    public long length() throws IOException {
        return this.max(this.fileendpos + 1, this.initfilelen);
    }

    public long getFilePointer() throws IOException {
        return this.curpos;
    }

    public void write(byte b[], int off, int len) throws IOException {
        long writeendpos = this.curpos + len - 1;
        if (writeendpos <= this.bufendpos) { // b[] in cur buf
System.arraycopy(b, off, this.buf, (int)(this.curpos - this.bufstartpos), 
len);
            this.bufdirty = true;
            this.bufusedsize = (int)(writeendpos - this.bufstartpos + 1);
        } else { // b[] not in cur buf
            super.seek(this.curpos);
            super.write(b, off, len);
        }
        if (writeendpos > this.fileendpos)
            this.fileendpos = writeendpos;
        this.seek(writeendpos+1);
}
    public void write(byte b[]) throws IOException {
        this.write(b, 0, b.length);
    }

public int read(byte b[], int off, int len) throws IOException {
long readendpos = this.curpos + len - 1;
   if (readendpos <= this.bufendpos && readendpos <= this.fileendpos ) { 
// read in buf
     	System.arraycopy(this.buf, (int)(this.curpos - this.bufstartpos), 
b, off, len);
   } else { // read b[] size > buf[]
   		if (readendpos > this.fileendpos) { // read b[] part in file
      		len = (int)(this.length() - this.curpos + 1);
       }
       super.seek(this.curpos);
       len = super.read(b, off, len);
       readendpos = this.curpos + len - 1;
   }
       this.seek(readendpos + 1);
       return len;
}
   public int read(byte b[]) throws IOException {
        return this.read(b, 0, b.length);
   }
public void setLength(long newLength) throws IOException {
        if (newLength > 0) {
            this.fileendpos = newLength - 1;
        } else {
            this.fileendpos = 0;
        }
        super.setLength(newLength);
}
    
public void close() throws IOException {
        this.flushbuf();
        super.close();
   	}

RandomAccessFile rafi = new RandomAccessFile(SrcFile, "r");
   RandomAccessFile rafo = new RandomAccessFile(DesFile, "rw");
	FileChannel fci = rafi.getChannel();
FileChannel fco = rafo.getChannel();
	long size = fci.size();
	MappedByteBuffer mbbi = fci.map(FileChannel.MapMode.READ_ONLY, 0, size);
MappedByteBuffer mbbo = fco.map(FileChannel.MapMode.READ_WRITE, 0, size);
long start = System.currentTimeMillis();
for (int i = 0; i < size; i++) {
            byte b = mbbi.get(i);
            mbbo.put(i, b);
}
fcin.close();
fcout.close();
rafi.close();
rafo.close();
System.out.println("Spend: "+(double)(System.currentTimeMillis()-start) / 1000 + "s");