组件化功能基本完成
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laoyuyu
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/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.arialyy.aria.util;
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import java.io.File;
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import java.io.FileNotFoundException;
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import java.io.IOException;
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import java.io.RandomAccessFile;
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import java.util.Arrays;
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/**
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* A <code>BufferedRandomAccessFile</code> is like a
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* <code>RandomAccessFile</code>, but it uses a private buffer so that most
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* operations do not require a disk access.
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* <P>
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*
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* Note: The operations on this class are unmonitored. Also, the correct
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* functioning of the <code>RandomAccessFile</code> methods that are not
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* overridden here relies on the implementation of those methods in the
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* superclass.
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* Author : Avinash Lakshman ( alakshman@facebook.com) Prashant Malik ( pmalik@facebook.com )
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*/
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public final class BufferedRandomAccessFile extends RandomAccessFile {
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//private static final Logger logger_ = Logger.getLogger(BufferedRandomAccessFile.class);
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static final int LogBuffSz_ = 16; // 64K buffer
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public static final int BuffSz_ = (1 << LogBuffSz_);
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static final long BuffMask_ = ~(((long) BuffSz_) - 1L);
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/*
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* This implementation is based on the buffer implementation in Modula-3's
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* "Rd", "Wr", "RdClass", and "WrClass" interfaces.
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*/
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private boolean dirty_; // true iff unflushed bytes exist
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private boolean closed_; // true iff the file is closed
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private long curr_; // current position in file
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private long lo_, hi_; // bounds on characters in "buff"
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private byte[] buff_; // local buffer
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private long maxHi_; // this.lo + this.buff.length
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private boolean hitEOF_; // buffer contains last file block?
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private long diskPos_; // disk position
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/*
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* To describe the above fields, we introduce the following abstractions for
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* the file "f":
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*
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* len(f) the length of the file curr(f) the current position in the file
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* c(f) the abstract contents of the file disk(f) the contents of f's
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* backing disk file closed(f) true iff the file is closed
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*
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* "curr(f)" is an peerIndex in the closed interval [0, len(f)]. "c(f)" is a
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* character sequence of length "len(f)". "c(f)" and "disk(f)" may differ if
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* "c(f)" contains unflushed writes not reflected in "disk(f)". The flush
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* operation has the effect of making "disk(f)" identical to "c(f)".
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*
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* A file is said to be *valid* if the following conditions hold:
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*
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* V1. The "closed" and "curr" fields are correct:
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*
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* f.closed == closed(f) f.curr == curr(f)
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*
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* V2. The current position is either contained in the buffer, or just past
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* the buffer:
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*
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* f.lo <= f.curr <= f.hi
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*
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* V3. Any (possibly) unflushed characters are stored in "f.buff":
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*
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* (forall i in [f.lo, f.curr): c(f)[i] == f.buff[i - f.lo])
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*
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* V4. For all characters not covered by V3, c(f) and disk(f) agree:
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*
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* (forall i in [f.lo, len(f)): i not in [f.lo, f.curr) => c(f)[i] ==
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* disk(f)[i])
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*
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* V5. "f.dirty" is true iff the buffer contains bytes that should be
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* flushed to the file; by V3 and V4, only part of the buffer can be dirty.
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*
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* f.dirty == (exists i in [f.lo, f.curr): c(f)[i] != f.buff[i - f.lo])
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*
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* V6. this.maxHi == this.lo + this.buff.length
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*
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* Note that "f.buff" can be "null" in a valid file, since the range of
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* characters in V3 is empty when "f.lo == f.curr".
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*
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* A file is said to be *ready* if the buffer contains the current position,
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* i.e., when:
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*
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* R1. !f.closed && f.buff != null && f.lo <= f.curr && f.curr < f.hi
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*
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* When a file is ready, reading or writing a single byte can be performed
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* by reading or writing the in-memory buffer without performing a disk
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* operation.
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*/
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/**
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* Open a new <code>BufferedRandomAccessFile</code> on <code>file</code>
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* in mode <code>mode</code>, which should be "r" for reading only, or
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* "rw" for reading and writing.
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*/
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public BufferedRandomAccessFile(File file, String mode) throws IOException {
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super(file, mode);
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this.init(0);
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}
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public BufferedRandomAccessFile(File file, String mode, int size) throws IOException {
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super(file, mode);
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this.init(size);
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}
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/**
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* Open a new <code>BufferedRandomAccessFile</code> on the file named
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* <code>name</code> in mode <code>mode</code>, which should be "r" for
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* reading only, or "rw" for reading and writing.
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*/
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public BufferedRandomAccessFile(String name, String mode) throws IOException {
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super(name, mode);
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this.init(0);
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}
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public BufferedRandomAccessFile(String name, String mode, int size) throws FileNotFoundException {
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super(name, mode);
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this.init(size);
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}
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private void init(int size) {
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this.dirty_ = this.closed_ = false;
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this.lo_ = this.curr_ = this.hi_ = 0;
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this.buff_ = (size > BuffSz_) ? new byte[size] : new byte[BuffSz_];
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this.maxHi_ = (long) BuffSz_;
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this.hitEOF_ = false;
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this.diskPos_ = 0L;
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}
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public void close() throws IOException {
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this.flush();
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this.closed_ = true;
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super.close();
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}
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/**
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* Flush any bytes in the file's buffer that have not yet been written to
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* disk. If the file was created read-only, this method is a no-op.
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*/
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public void flush() throws IOException {
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this.flushBuffer();
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}
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/* Flush any dirty bytes in the buffer to disk. */
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private void flushBuffer() throws IOException {
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if (this.dirty_) {
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if (this.diskPos_ != this.lo_) super.seek(this.lo_);
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int len = (int) (this.curr_ - this.lo_);
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super.write(this.buff_, 0, len);
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this.diskPos_ = this.curr_;
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this.dirty_ = false;
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}
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}
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/*
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* Read at most "this.buff.length" bytes into "this.buff", returning the
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* number of bytes read. If the return result is less than
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* "this.buff.length", then EOF was read.
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*/
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private int fillBuffer() throws IOException {
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int cnt = 0;
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int rem = this.buff_.length;
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while (rem > 0) {
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int n = super.read(this.buff_, cnt, rem);
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if (n < 0) break;
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cnt += n;
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rem -= n;
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}
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if ((cnt < 0) && (this.hitEOF_ = (cnt < this.buff_.length))) {
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// make sure buffer that wasn't read is initialized with -1
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Arrays.fill(this.buff_, cnt, this.buff_.length, (byte) 0xff);
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}
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this.diskPos_ += cnt;
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return cnt;
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}
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/*
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* This method positions <code>this.curr</code> at position <code>pos</code>.
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* If <code>pos</code> does not fall in the current buffer, it flushes the
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* current buffer and loads the correct one.<p>
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*
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* On exit from this routine <code>this.curr == this.hi</code> iff <code>pos</code>
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* is at or past the end-of-file, which can only happen if the file was
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* opened in read-only mode.
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*/
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public void seek(long pos) throws IOException {
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if (pos >= this.hi_ || pos < this.lo_) {
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// seeking outside of current buffer -- flush and read
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this.flushBuffer();
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this.lo_ = pos & BuffMask_; // create at BuffSz boundary
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this.maxHi_ = this.lo_ + (long) this.buff_.length;
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if (this.diskPos_ != this.lo_) {
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super.seek(this.lo_);
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this.diskPos_ = this.lo_;
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}
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int n = this.fillBuffer();
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this.hi_ = this.lo_ + (long) n;
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} else {
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// seeking inside current buffer -- no read required
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if (pos < this.curr_) {
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// if seeking backwards, we must flush to maintain V4
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this.flushBuffer();
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}
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}
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this.curr_ = pos;
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}
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public long getFilePointer() {
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return this.curr_;
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}
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public long length() throws IOException {
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return Math.max(this.curr_, super.length());
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}
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public int read() throws IOException {
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if (this.curr_ >= this.hi_) {
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// test for EOF
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// if (this.hi < this.maxHi) return -1;
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if (this.hitEOF_) return -1;
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// slow path -- read another buffer
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this.seek(this.curr_);
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if (this.curr_ == this.hi_) return -1;
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}
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byte res = this.buff_[(int) (this.curr_ - this.lo_)];
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this.curr_++;
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return ((int) res) & 0xFF; // convert byte -> int
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}
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public int read(byte[] b) throws IOException {
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return this.read(b, 0, b.length);
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}
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public int read(byte[] b, int off, int len) throws IOException {
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if (this.curr_ >= this.hi_) {
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// test for EOF
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// if (this.hi < this.maxHi) return -1;
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if (this.hitEOF_) return -1;
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// slow path -- read another buffer
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this.seek(this.curr_);
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if (this.curr_ == this.hi_) return -1;
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}
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len = Math.min(len, (int) (this.hi_ - this.curr_));
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int buffOff = (int) (this.curr_ - this.lo_);
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System.arraycopy(this.buff_, buffOff, b, off, len);
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this.curr_ += len;
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return len;
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}
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public void write(int b) throws IOException {
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if (this.curr_ >= this.hi_) {
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if (this.hitEOF_ && this.hi_ < this.maxHi_) {
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// at EOF -- bump "hi"
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this.hi_++;
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} else {
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// slow path -- write current buffer; read next one
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this.seek(this.curr_);
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if (this.curr_ == this.hi_) {
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// appending to EOF -- bump "hi"
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this.hi_++;
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}
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}
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}
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this.buff_[(int) (this.curr_ - this.lo_)] = (byte) b;
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this.curr_++;
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this.dirty_ = true;
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}
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public void write(byte[] b) throws IOException {
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this.write(b, 0, b.length);
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}
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public void write(byte[] b, int off, int len) throws IOException {
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while (len > 0) {
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int n = this.writeAtMost(b, off, len);
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off += n;
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len -= n;
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this.dirty_ = true;
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}
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}
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/*
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* Write at most "len" bytes to "b" starting at position "off", and return
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* the number of bytes written.
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*/
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private int writeAtMost(byte[] b, int off, int len) throws IOException {
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if (this.curr_ >= this.hi_) {
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if (this.hitEOF_ && this.hi_ < this.maxHi_) {
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// at EOF -- bump "hi"
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this.hi_ = this.maxHi_;
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} else {
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// slow path -- write current buffer; read next one
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this.seek(this.curr_);
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if (this.curr_ == this.hi_) {
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// appending to EOF -- bump "hi"
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this.hi_ = this.maxHi_;
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}
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}
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}
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len = Math.min(len, (int) (this.hi_ - this.curr_));
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int buffOff = (int) (this.curr_ - this.lo_);
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System.arraycopy(b, off, this.buff_, buffOff, len);
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this.curr_ += len;
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return len;
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}
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}
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