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;
}
</span>

<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;
}
}
</wbr></span>

<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;
}
}
}
</wbr></span>

<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 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);
}
}
</wbr></span>

<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 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 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。
...
}
</span>

<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);
}
</span>

<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 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);
}
</span>

<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 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();
}
</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");
</span>