MappedByteBuffer的学习

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package com.taobao.danchen.bytebuffer;import java.io.File;import java.io.IOException;import java.io.RandomAccessFile;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;public class MappedFile {    // 文件名    private String fileName;    // 文件路径    private String filePath;    // 文件对象    private File file;    private MappedByteBuffer mappedByteBuffer;    private FileChannel fileChannel;    private boolean bundSuccess = false;    // 文件大小    private final static long MAX_FILE_SIZE = 1024 * 1024 * 50;    // 文件写入位置    private long writePosition = 0;    // 最后一次刷数据的时间    private long lastFlushTime;    // 上一次刷的文件位置    private long lastFlushFilePosition = 0;    // 最大的脏数据量，系统必须触发一次强制刷    private long MAX_FLUSH_DATA_SIZE = 1024 * 512;    // 最大的时间间隔，系统必须触发一次强制刷    private long MAX_FLUSH_TIME_GAP = 1000;    public MappedFile(String fileName, String filePath) {super();this.fileName = fileName;this.filePath = filePath;this.file = new File(filePath + "/" + fileName);if (!file.exists()) {    try {file.createNewFile();    } catch (IOException e) {e.printStackTrace();    }}    }    /**     * 内存映射文件绑定     *      * @return     */    public synchronized boolean boundChannelToByteBuffer() {try {    RandomAccessFile raf = new RandomAccessFile(file, "rw");    this.fileChannel = raf.getChannel();} catch (Exception e) {    e.printStackTrace();    this.bundSuccess = false;    return false;}try {    this.mappedByteBuffer = this.fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, MAX_FILE_SIZE);} catch (IOException e) {    e.printStackTrace();    this.bundSuccess = false;    return false;}this.bundSuccess = true;return true;    }    public synchronized boolean appendData(byte[] data) throws Exception {if (!bundSuccess) {    throw new Exception("内存映射文件没有建立,请检查...");}writePosition = writePosition + data.length;if (writePosition >= MAX_FILE_SIZE) {    flush();    writePosition = writePosition - data.length;    System.out.println("File=" + file.toURI().toString() + " is writed full.");    System.out.println("already write data length:" + writePosition + "max file size=" + MAX_FILE_SIZE);    return false;}this.mappedByteBuffer.put(data);// 检测修改量if (writePosition - lastFlushFilePosition > this.MAX_FLUSH_DATA_SIZE) {    flush();}// 检测时间间隔if (System.currentTimeMillis() - lastFlushTime > this.MAX_FLUSH_TIME_GAP && writePosition > lastFlushFilePosition) {    flush();}return true;    }    public synchronized void flush() {this.mappedByteBuffer.force();this.lastFlushTime = System.currentTimeMillis();this.lastFlushFilePosition = writePosition;    }    public long getLastFlushTime() {return lastFlushTime;    }    public String getFileName() {return fileName;    }    public String getFilePath() {return filePath;    }    public boolean isBundSuccess() {return bundSuccess;    }    public File getFile() {return file;    }    public static long getMaxFileSize() {return MAX_FILE_SIZE;    }    public long getWritePosition() {return writePosition;    }    public long getLastFlushFilePosition() {return lastFlushFilePosition;    }    public long getMAX_FLUSH_DATA_SIZE() {return MAX_FLUSH_DATA_SIZE;    }    public long getMAX_FLUSH_TIME_GAP() {return MAX_FLUSH_TIME_GAP;    }}
转载自：http://zhaolinjnu.blog.sohu.com/265626071.html
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