/*
* Copyright (C) 2014 hu
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
package cn.edu.hfut.dmic.webcollector.generator;
import cn.edu.hfut.dmic.webcollector.model.CrawlDatum;
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import org.apache.avro.file.DataFileReader;
import org.apache.avro.io.DatumReader;
import org.apache.avro.reflect.ReflectDatumReader;
/**
* 读Avro文件的Reader
* @author hu
* @param <T> 待读取数据的数据类型
*/
public class DbReader<T> {
Class<T> type;
Iterator<T> iterator;
DataFileReader<T> dataFileReader;
/**
* 构造一个从avro文件中读取指定类型数据的Reader
* @param type 指定的数据类型
* @param dbfile 待读取的avro文件
* @throws IOException
*/
public DbReader(Class<T> type,File dbfile) throws IOException {
this.type=type;
DatumReader<T> datumReader = new ReflectDatumReader<T>(type);
dataFileReader = new DataFileReader<T>(dbfile, datumReader);
iterator = dataFileReader.iterator();
}
/**
* 构造一个从avro文件中读取指定类型数据的Reader
* @param type 指定的数据类型
* @param dbpath 待读取的avro文件的路径
* @throws IOException
*/
public DbReader(Class<T> type,String dbpath) throws IOException {
this(type,new File(dbpath));
}
/**
* 读取下一条数据，在文件结束时调用该方法会出错，所以在调用readNext方法前需要使
* 用hasNext方法来判断文件是否结束
* @return 下一条数据
*/
public T readNext() {
return iterator.next();
}
/**
* 判断是否已读取到avro文件结尾
* @return 是否已读取到avro文件结尾
*/
public boolean hasNext(){
return iterator.hasNext();
}
/**
* 关闭该Reader
* @throws IOException
*/
public void close() throws IOException {
dataFileReader.close();
}
public static void main(String[] args) throws IOException{
if(args.length==0){
System.err.println("Usage dbpath");
main(new String[]{"/home/hu/data/crawl_hfut1/crawldb/current/info.avro"});
return;
}
String dbpath=args[0];
DbReader<CrawlDatum> reader=new DbReader<CrawlDatum>(CrawlDatum.class,dbpath);
int sum=0;
int sum_fetched=0;
int sum_unfetched=0;
CrawlDatum crawldatum=null;
System.out.println("start read:");
while(reader.hasNext()){
crawldatum=reader.readNext();
System.out.println(crawldatum.getUrl());
sum++;
switch(crawldatum.getStatus()){
case CrawlDatum.STATUS_DB_FETCHED:
sum_fetched++;
break;
case CrawlDatum.STATUS_DB_UNFETCHED:
sum_unfetched++;
break;
}
}
reader.close();
}
}