cc.shacocloud.mirage.loader.data.RandomAccessDataFile Maven / Gradle / Ivy
package cc.shacocloud.mirage.loader.data;
import java.io.*;
/**
* {@link RandomAccessData} 实现由 {@link RandomAccessFile} 支持
*/
public class RandomAccessDataFile implements RandomAccessData {
private final FileAccess fileAccess;
private final long offset;
private final long length;
/**
* 创建一个由指定文件支持的新 {@link RandomAccessDataFile}
*
* @param file 基础文件
* @throws IllegalArgumentException 如果文件为空或不存在
*/
public RandomAccessDataFile(File file) {
if (file == null) {
throw new IllegalArgumentException("文件不得为空");
}
this.fileAccess = new FileAccess(file);
this.offset = 0L;
this.length = file.length();
}
/**
* 用于创建 {@link #getSubsection(long, long)} 的私有构造函数
*/
private RandomAccessDataFile(FileAccess fileAccess, long offset, long length) {
this.fileAccess = fileAccess;
this.offset = offset;
this.length = length;
}
/**
* 返回基础文件
*/
public File getFile() {
return this.fileAccess.file;
}
@Override
public InputStream getInputStream() throws IOException {
return new DataInputStream();
}
@Override
public RandomAccessData getSubsection(long offset, long length) {
if (offset < 0 || length < 0 || offset + length > this.length) {
throw new IndexOutOfBoundsException();
}
return new RandomAccessDataFile(this.fileAccess, this.offset + offset, length);
}
@Override
public byte[] read() throws IOException {
return read(0, this.length);
}
@Override
public byte[] read(long offset, long length) throws IOException {
if (offset > this.length) {
throw new IndexOutOfBoundsException();
}
if (offset + length > this.length) {
throw new EOFException();
}
byte[] bytes = new byte[(int) length];
read(bytes, offset, 0, bytes.length);
return bytes;
}
private int readByte(long position) throws IOException {
if (position >= this.length) {
return -1;
}
return this.fileAccess.readByte(this.offset + position);
}
private int read(byte[] bytes, long position, int offset, int length) throws IOException {
if (position > this.length) {
return -1;
}
return this.fileAccess.read(bytes, this.offset + position, offset, length);
}
@Override
public long getSize() {
return this.length;
}
public void close() throws IOException {
this.fileAccess.close();
}
/**
* {@link InputStream} 实现 {@link RandomAccessDataFile}
*/
private class DataInputStream extends InputStream {
private int position;
@Override
public int read() throws IOException {
int read = RandomAccessDataFile.this.readByte(this.position);
if (read > -1) {
moveOn(1);
}
return read;
}
@Override
public int read(byte[] b) throws IOException {
return read(b, 0, (b != null) ? b.length : 0);
}
@Override
public int read(byte[] b, int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException("Bytes must not be null");
}
return doRead(b, off, len);
}
/**
* 执行实际读取
*
* @param b 读取单个字节时要读取的字节数或 {@code null}
* @param off 字节数组的偏移量
* @param len 要读取的数据长度
* @return 读入 {@code b} 的字节数或实际读取字节数（如果 {@code b} 为 {@code null}。到达流的末尾时返回 -1
*/
int doRead(byte[] b, int off, int len) throws IOException {
if (len == 0) {
return 0;
}
int cappedLen = cap(len);
if (cappedLen <= 0) {
return -1;
}
return (int) moveOn(RandomAccessDataFile.this.read(b, this.position, off, cappedLen));
}
@Override
public long skip(long n) throws IOException {
return (n <= 0) ? 0 : moveOn(cap(n));
}
@Override
public int available() throws IOException {
return (int) RandomAccessDataFile.this.length - this.position;
}
/**
* 限制指定值，使其不能超过剩余字节数
*/
private int cap(long n) {
return (int) Math.min(RandomAccessDataFile.this.length - this.position, n);
}
/**
* 将流位置向前移动指定的量
*/
private long moveOn(int amount) {
this.position += amount;
return amount;
}
}
private static final class FileAccess {
private final Object monitor = new Object();
private final File file;
private RandomAccessFile randomAccessFile;
private FileAccess(File file) {
this.file = file;
openIfNecessary();
}
private int read(byte[] bytes, long position, int offset, int length) throws IOException {
synchronized (this.monitor) {
openIfNecessary();
this.randomAccessFile.seek(position);
return this.randomAccessFile.read(bytes, offset, length);
}
}
private void openIfNecessary() {
if (this.randomAccessFile == null) {
try {
this.randomAccessFile = new RandomAccessFile(this.file, "r");
} catch (FileNotFoundException ex) {
throw new IllegalArgumentException(String.format("文件 %s 必须存在", this.file.getAbsolutePath()));
}
}
}
private void close() throws IOException {
synchronized (this.monitor) {
if (this.randomAccessFile != null) {
this.randomAccessFile.close();
this.randomAccessFile = null;
}
}
}
private int readByte(long position) throws IOException {
synchronized (this.monitor) {
openIfNecessary();
this.randomAccessFile.seek(position);
return this.randomAccessFile.read();
}
}
}
}
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