创建Hadoop序列文件

Question

我正在尝试创建hadoop序列文件。

我成功地在HDFS中创建了一个序列文件，但是如果我试图读取一个序列文件，就会出现“sequence file not a SequenceFile”错误。我还检查一个在HDFS中创建的序列文件。

这里是我的源代码，可以读写序列文件到HDFS。

package us.qi.hdfs;

import java.io.IOException;
import java.net.URI;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.ArrayFile;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;

public class SequenceFileText {
    public static void main(String args[]) throws IOException {

        /** Get Hadoop HDFS command and Hadoop Configuration*/
        HDFS_Configuration conf = new html" target="_blank">HDFS_Configuration();
        HDFS_Test hdfs = new HDFS_Test();

        String uri = "hdfs://slave02:9000/user/hadoop/test.seq";

        /** Get Configuration from HDFS_Configuration Object by using get_conf()*/
        Configuration config = conf.get_conf();

        SequenceFile.Writer writer = null;
        SequenceFile.Reader reader = null;

        try {
            Path path = new Path(uri);

            IntWritable key = new IntWritable();
            Text value = new Text();

            writer = SequenceFile.createWriter(config, SequenceFile.Writer.file(path), SequenceFile.Writer.keyClass(key.getClass()),
                    ArrayFile.Writer.valueClass(value.getClass()));
            reader = new SequenceFile.Reader(config, SequenceFile.Reader.file(path));

            writer.append(new IntWritable(11), new Text("test"));
            writer.append(new IntWritable(12), new Text("test2"));
            writer.close();

            while (reader.next(key, value)) {
                System.out.println(key + "\t" + value);
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            IOUtils.closeStream(writer);
            IOUtils.closeStream(reader);
        }
    }
}

2018-09-17 17:15:34,267 WARN[main]util.nativeCodeLoader（nativeCodeLoader.java：（62））-无法为您的平台加载本机Hadoop库...使用内置-适用的Java类2018-09-17 17:15:38,870 INFO[main]compress.codecpool（codecpool.java:getcompressor(153))-获得了全新的压缩器[.deflate]java.io.eofexception：hdfs：//slave02:9000/user/hadoop/test.seq不是org.apache.hadoop.io.SequenceFile$reader.init（SequenceFile：1933）在org.apache.hadoop.io.SequenceFile$reader.initialize（

Answer 1

那是我的错误。我修改了一些源代码。

首先，我检查文件是否已经存在于HDFS中。如果没有文件，我就创建一个writer对象。

当writer进程完成时，我检查序列文件。检查文件后，我成功地读取了一个序列文件。

try {
            Path path = new Path(uri);

            IntWritable key = new IntWritable();
            Text value = new Text();

            /** First, Check a file already exists.
             * If there is not exists in hdfs, writer object is created.
             * */
            if (!fs.exists(path)) {
                writer = SequenceFile.createWriter(config, SequenceFile.Writer.file(path), SequenceFile.Writer.keyClass(key.getClass()),
                        ArrayFile.Writer.valueClass(value.getClass()));

                writer.append(new IntWritable(11), new Text("test"));
                writer.append(new IntWritable(12), new Text("test2"));
                writer.close();
            } else {
                logger.info(path + " already exists.");
            }

            /** Create a SequenceFile Reader object.*/
            reader = new SequenceFile.Reader(config, SequenceFile.Reader.file(path));

            while (reader.next(key, value)) {
                System.out.println(key + "\t" + value);
            }

            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            IOUtils.closeStream(writer);
            IOUtils.closeStream(reader);
        }