FileMixedRecordPositioner.java

package com.taobao.yugong.positioner;

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.commons.io.FileUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.util.Assert;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.taobao.yugong.common.model.position.Position;
import com.taobao.yugong.exception.YuGongException;

/**
 * 基于文件刷新的position实现
 * 
 * <pre>
 * 策略：
 * 1. 先写内存，然后定时刷新数据到File
 * 2. 数据采取overwrite模式(只保留最后一次)
 * </pre>
 * 
 * @author agapple 2013-9-22 下午3:37:13
 */
public class FileMixedRecordPositioner extends MemoryRecordPositioner implements RecordPositioner {

    private static final Logger      logger       = LoggerFactory.getLogger(FileMixedRecordPositioner.class);
    private static final Charset     charset      = Charset.forName("UTF-8");
    private File                     dataDir;
    private String                   dataFileName = "position.dat";
    private File                     dataFile;
    private ScheduledExecutorService executor;
    private long                     period       = 100;                                                     // 单位ms

    private AtomicBoolean            needFlush    = new AtomicBoolean(false);
    private AtomicBoolean            needReload   = new AtomicBoolean(true);

    public void start() {
        super.start();

        Assert.notNull(dataDir);
        if (!dataDir.exists()) {
            try {
                FileUtils.forceMkdir(dataDir);
            } catch (IOException e) {
                throw new YuGongException(e);
            }
        }

        if (!dataDir.canRead() || !dataDir.canWrite()) {
            throw new YuGongException("dir[" + dataDir.getPath() + "] can not read/write");
        }

        dataFile = new File(dataDir, dataFileName);

        executor = Executors.newScheduledThreadPool(1);
        // 启动定时工作任务
        executor.scheduleAtFixedRate(new Runnable() {

            public void run() {
                try {
                    // 定时将内存中的最新值刷到file中，多次变更只刷一次
                    if (needFlush.compareAndSet(true, false)) {
                        flushDataToFile(dataFile, getLatest());
                    }
                } catch (Throwable e) {
                    // ignore
                    logger.error("period update position failed!", e);
                }
            }
        }, period, period, TimeUnit.MILLISECONDS);
    }

    public void stop() {
        super.stop();

        flushDataToFile(dataFile, super.getLatest());
        executor.shutdownNow();
    }

    public void persist(Position position) {
        needFlush.set(true);
        super.persist(position);
    }

    public Position getLatest() {
        if (needReload.compareAndSet(true, false)) {
            Position position = loadDataFromFile(dataFile);
            super.persist(position);
            return position;
        } else {
            return super.getLatest();
        }
    }

    // ============================ helper method ======================

    private void flushDataToFile(File dataFile, Position position) {
        if (position != null) {
            String json = JSON.toJSONString(position,
                SerializerFeature.WriteClassName,
                SerializerFeature.WriteNullListAsEmpty);
            try {
                FileUtils.writeStringToFile(dataFile, json);
            } catch (IOException e) {
                throw new YuGongException(e);
            }
        }
    }

    private Position loadDataFromFile(File dataFile) {
        try {
            if (!dataFile.exists()) {
                return null;
            }

            String json = FileUtils.readFileToString(dataFile, charset.name());
            return JSON.parseObject(json, Position.class);
        } catch (IOException e) {
            throw new YuGongException(e);
        }
    }

    public void setDataDir(File dataDir) {
        this.dataDir = dataDir;
    }

    public void setDataFileName(String dataFileName) {
        this.dataFileName = dataFileName;
    }

    public void setPeriod(long period) {
        this.period = period;
    }

}