Java的随机读写文件-RandomAccessFile 与内存映射

<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">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; 
}
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<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">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<wbr>("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;            else if (pos >= buf.length)     if (markpos > 0) {  int sz = pos - markpos;System.arraycopy(buf, markpos, buf, 0, sz);pos = sz;markpos = 0;} else if (buf.length >= marklimit) {markpos = -1;   pos = 0;        } else {            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;}
}
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<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">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<wbr>("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;}}
}
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<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">public class BufferedRandomAccessFile<wbr> 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 bufthis.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 posthis.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);}
}
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<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">// 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 bufthis.buf[(int)(pos - this.bufstartpos)] = bw;this.bufdirty = true;if (pos == this.fileendpos + 1) { // write pos is append posthis.fileendpos++;this.bufusedsize++;}} else { // write pos not in bufthis.seek(pos);if ((pos >= 0) && (pos <= this.fileendpos) && (this.fileendpos != 0)) 
{ // write pos is modify filethis.buf[(int)(pos - this.bufstartpos)] = bw;} else if (((pos == 0) && (this.fileendpos == 0)) 
|| (pos == this.fileendpos + 1)) { // write pos is append posthis.buf[0] = bw;this.fileendpos++;this.bufusedsize = 1;} else {throw new IndexOutOfBoundsExceptio<wbr>n();}this.bufdirty = true;}this.curpos = pos;return true;}</wbr></span>

<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">   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。
...
}
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<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">    public boolean append(byte bw) throws IOException {return this.write(bw, this.fileendpos + 1);}
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<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">    public boolean write(byte bw) throws IOException {return this.write(bw, this.curpos);}</span>

<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">    public long length() throws IOException {return this.max(this.fileendpos + 1, this.initfilelen);}</span>

<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">    public long getFilePointer() throws IOException {return this.curpos;}</span>

<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">    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 bufsuper.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);}
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<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">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 bufSystem.arraycopy(this.buf, (int)(this.curpos - this.bufstartpos), 
b, off, len);} else { // read b[] size > buf[]if (readendpos > this.fileendpos) { // read b[] part in filelen = (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();}</span>

<span style="word-wrap: normal; word-break: normal; line-height: 16.5px; background-color: rgb(255, 255, 255);">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");
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