import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;/**
* 版权所有：
* 项目名称:
* 创建者: diaoby
* 创建日期:
* 文件说明:*/
public classBufferedRandomAccessFile extends RandomAccessFile {static final int LogBuffSz_ = 16; //64K buffer
public static final int BuffSz_ = (1 <
* “Rd”, “Wr”, “RdClass”, and “WrClass” interfaces.*/
private boolean dirty_; //true iff unflushed bytes exist
private boolean syncNeeded_; //dirty_ can be cleared by e.g. seek, so track sync separately
private long curr_; //current position in file
private long lo_, hi_; //bounds on characters in “buff”
private byte[] buff_; //local buffer
private long maxHi_; //this.lo + this.buff.length
private boolean hitEOF_; //buffer contains last file block?
private long diskPos_; //disk position
/** To describe the above fields, we introduce the following abstractions for
* the file “f”:
*
* len(f) the length of the file curr(f) the current position in the file
* c(f) the abstract contents of the file disk(f) the contents of f’s
* backing disk file closed(f) true iff the file is closed
*
* “curr(f)” is an index in the closed interval [0, len(f)]. “c(f)” is a
* character sequence of length “len(f)”. “c(f)” and “disk(f)” may differ if
* “c(f)” contains unflushed writes not reflected in “disk(f)”. The flush
* operation has the effect of making “disk(f)” identical to “c(f)”.
*
* A file is said to be *valid* if the following conditions hold:
*
* V1. The “closed” and “curr” fields are correct:
*
* f.closed == closed(f) f.curr == curr(f)
*
* V2. The current position is either contained in the buffer, or just past
* the buffer:
*
* f.lo <= f.curr <= f.hi
*
* V3. Any (possibly) unflushed characters are stored in “f.buff”:
*
* (forall i in [f.lo, f.curr): c(f)[i] == f.buff[i – f.lo])
*
* V4. For all characters not covered by V3, c(f) and disk(f) agree:
*
* (forall i in [f.lo, len(f)): i not in [f.lo, f.curr) => c(f)[i] ==
* disk(f)[i])
*
* V5. “f.dirty” is true iff the buffer contains bytes that should be
* flushed to the file; by V3 and V4, only part of the buffer can be dirty.
*
* f.dirty == (exists i in [f.lo, f.curr): c(f)[i] != f.buff[i – f.lo])
*
* V6. this.maxHi == this.lo + this.buff.length
*
* Note that “f.buff” can be “null” in a valid file, since the range of
* characters in V3 is empty when “f.lo == f.curr”.
*
* A file is said to be *ready* if the buffer contains the current position,
* i.e., when:
*
* R1. !f.closed && f.buff != null && f.lo <= f.curr && f.curr < f.hi
*
* When a file is ready, reading or writing a single byte can be performed
* by reading or writing the in-memory buffer without performing a disk
* operation.*/
/**
* Open a new
BufferedRandomAccessFile
on
file
* in mode
mode
, which should be “r” for reading only, or
* “rw” for reading and writing.*/
publicBufferedRandomAccessFile(File file, String mode) throws IOException {this(file, mode, 0);
}public BufferedRandomAccessFile(File file, String mode, intsize) throws IOException {
super(file, mode);
path_=file.getAbsolutePath();this.init(size);
}/**
* Open a new
BufferedRandomAccessFile
on the file named
*
name
in mode
mode
, which should be “r” for
* reading only, or “rw” for reading and writing.*/
publicBufferedRandomAccessFile(String name, String mode) throws IOException {this(name, mode, 0);
}public BufferedRandomAccessFile(String name, String mode, intsize) throws FileNotFoundException {
super(name, mode);
path_=name;this.init(size);
}private void init(intsize) {this.dirty_ = false;this.lo_ = this.curr_ = this.hi_ = 0;this.buff_ = (size > BuffSz_) ? new byte[size] : new byte[BuffSz_];this.maxHi_ = (long) BuffSz_;this.hitEOF_ = false;this.diskPos_ = 0L;
}publicString getPath() {returnpath_;
}public voidsync() throws IOException {if(syncNeeded_) {
flush();
getChannel().force(true);
syncNeeded_= false;
}
}//public boolean isEOF() throws IOException//{//assert getFilePointer() <= length();//return getFilePointer() == length();//}
public voidclose() throws IOException {this.flush();this.buff_ = null;
super.close();
}/**
* Flush any bytes in the file’s buffer that have not yet been written to
* disk. If the file was created read-only, this method is a no-op.*/
public voidflush() throws IOException {this.flushBuffer();
}/*Flush any dirty bytes in the buffer to disk.*/
private voidflushBuffer() throws IOException {if (this.dirty_) {if (this.diskPos_ != this.lo_)
super.seek(this.lo_);int len = (int) (this.curr_ – this.lo_);
super.write(this.buff_, 0, len);this.diskPos_ = this.curr_;this.dirty_ = false;
}
}/** Read at most “this.buff.length” bytes into “this.buff”, returning the
* number of bytes read. If the return result is less than
* “this.buff.length”, then EOF was read.*/
private intfillBuffer() throws IOException {int cnt = 0;int rem = this.buff_.length;while (rem > 0) {int n = super.read(this.buff_, cnt, rem);if (n < 0)break;
cnt+=n;
rem-=n;
}if ((cnt < 0) && (this.hitEOF_ = (cnt < this.buff_.length))) {//make sure buffer that wasn’t read is initialized with -1
Arrays.fill(this.buff_, cnt, this.buff_.length, (byte) 0xff);
}this.diskPos_ +=cnt;returncnt;
}/** This method positions
this.curr
at position
pos
.
* If
pos
does not fall in the current buffer, it flushes the
* current buffer and loads the correct one.
*
* On exit from this routine
this.curr == this.hi
iff
pos
* is at or past the end-of-file, which can only happen if the file was
* opened in read-only mode.*/
public void seek(longpos) throws IOException {if (pos >= this.hi_ || pos < this.lo_) {//seeking outside of current buffer — flush and read
this.flushBuffer();this.lo_ = pos & BuffMask_; //start at BuffSz boundary
this.maxHi_ = this.lo_ + (long) this.buff_.length;if (this.diskPos_ != this.lo_) {
super.seek(this.lo_);this.diskPos_ = this.lo_;
}int n = this.fillBuffer();this.hi_ = this.lo_ + (long) n;
}else{//seeking inside current buffer — no read required
if (pos < this.curr_) {//if seeking backwards, we must flush to maintain V4
this.flushBuffer();
}
}this.curr_ =pos;
}public longgetFilePointer() {return this.curr_;
}public longlength() throws IOException {//max accounts for the case where we have written past the old file length, but not yet flushed our buffer
return Math.max(this.curr_, super.length());
}public intread() throws IOException {if (this.curr_ >= this.hi_) {//test for EOF//if (this.hi < this.maxHi) return -1;
if (this.hitEOF_)return -1;//slow path — read another buffer
this.seek(this.curr_);if (this.curr_ == this.hi_)return -1;
}byte res = this.buff_[(int) (this.curr_ – this.lo_)];this.curr_++;return ((int) res) & 0xFF; //convert byte -> int
}public int read(byte[] b) throws IOException {return this.read(b, 0, b.length);
}public int read(byte[] b, int off, intlen) throws IOException {if (this.curr_ >= this.hi_) {//test for EOF//if (this.hi < this.maxHi) return -1;
if (this.hitEOF_)return -1;//slow path — read another buffer
this.seek(this.curr_);if (this.curr_ == this.hi_)return -1;
}
len= Math.min(len, (int) (this.hi_ – this.curr_));int buffOff = (int) (this.curr_ – this.lo_);
System.arraycopy(this.buff_, buffOff, b, off, len);this.curr_ +=len;returnlen;
}public void write(intb) throws IOException {if (this.curr_ >= this.hi_) {if (this.hitEOF_ && this.hi_ < this.maxHi_) {//at EOF — bump “hi”
this.hi_++;
}else{//slow path — write current buffer; read next one
this.seek(this.curr_);if (this.curr_ == this.hi_) {//appending to EOF — bump “hi”
this.hi_++;
}
}
}this.buff_[(int) (this.curr_ – this.lo_)] = (byte) b;this.curr_++;this.dirty_ = true;
syncNeeded_= true;
}public void write(byte[] b) throws IOException {this.write(b, 0, b.length);
}public void write(byte[] b, int off, intlen) throws IOException {while (len > 0) {int n = this.writeAtMost(b, off, len);
off+=n;
len-=n;this.dirty_ = true;
syncNeeded_= true;
}
}/** Write at most “len” bytes to “b” starting at position “off”, and return
* the number of bytes written.*/
private int writeAtMost(byte[] b, int off, intlen) throws IOException {if (this.curr_ >= this.hi_) {if (this.hitEOF_ && this.hi_ < this.maxHi_) {//at EOF — bump “hi”
this.hi_ = this.maxHi_;
}else{//slow path — write current buffer; read next one
this.seek(this.curr_);if (this.curr_ == this.hi_) {//appending to EOF — bump “hi”
this.hi_ = this.maxHi_;
}
}
}
len= Math.min(len, (int) (this.hi_ – this.curr_));int buffOff = (int) (this.curr_ – this.lo_);
System.arraycopy(b, off,this.buff_, buffOff, len);this.curr_ +=len;returnlen;
}
}