3

The following code simply writes data into avro format and reads and displays the same from the avro file written too. I was just trying out the example in the Hadoop definitive guide book. I was able to execute this first time. Then I got the following error. It did work for the first time. So I am not sure wat mistake i am making.

This is the exception:

Exception in thread "main" java.io.EOFException: No content to map to Object due to end of input
    at org.codehaus.jackson.map.ObjectMapper._initForReading(ObjectMapper.java:2173)
    at org.codehaus.jackson.map.ObjectMapper._readValue(ObjectMapper.java:2106)
    at org.codehaus.jackson.map.ObjectMapper.readTree(ObjectMapper.java:1065)
    at org.codehaus.jackson.map.ObjectMapper.readTree(ObjectMapper.java:1040)
    at org.apache.avro.Schema.parse(Schema.java:895)
    at org.avro.example.SimpleAvro.AvroExample.avrocreate(AvroDataExample.java:23)
    at org.avro.example.SimpleAvro.AvroDataExample.main(AvroDataExample.java:55)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:156)

This is the code:

package org.avro.example.SimpleAvro;

import java.io.File;
import java.io.IOException;

import org.apache.avro.Schema;
import org.apache.avro.file.DataFileReader;
import org.apache.avro.file.DataFileWriter;
import org.apache.avro.generic.GenericData;
import org.apache.avro. generic.GenericDatumReader;
import org.apache.avro.generic.GenericDatumWriter;
import org.apache.avro.generic.GenericRecord;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.DatumWriter;

class AvroExample{

    AvroExample(){

    }
    void avrocreate() throws Exception{

        Schema schema=Schema.parse(getClass().getResourceAsStream("Pair.avsc"));

        GenericRecord datum=new GenericData.Record(schema);
        datum.put("left", "L");
        datum.put("right", "R");

        File file=new File("data.avro");
        DatumWriter<GenericRecord> writer=new GenericDatumWriter<GenericRecord>(schema);
        DataFileWriter<GenericRecord> dataFileWriter=new DataFileWriter<GenericRecord>(writer);
        dataFileWriter.create(schema, file);
        dataFileWriter.append(datum);
        dataFileWriter.close();

        System.out.println("Written to avro data file");
        //reading from the avro data file

        DatumReader<GenericRecord> reader= new GenericDatumReader<GenericRecord>();
        DataFileReader<GenericRecord> dataFileReader=new DataFileReader<GenericRecord>(file,reader);
        GenericRecord result=dataFileReader.next();
        System.out.println("data" + result.get("left").toString());

        result=dataFileReader.next();
        System.out.println("data :" + result.get("left").toString());


    }

}
public class AvroDataExample {
    public static void main(String args[])throws Exception{

        AvroExample a=new AvroExample();
        a.avrocreate();
    }



}

The following is the Pair.avsc file [ given in the book's example code]

{
  "type": "record",
  "name": "Pair",
  "doc": "A pair of strings.",
  "fields": [
    {"name": "left", "type": "string"},
    {"name": "right", "type": "string"}
  ]
}
4

3 回答 3

3

您可能没有正确读取架构文件。我怀疑这是问题所在，因为堆栈跟踪显示它无法解析架构：

Exception in thread "main" java.io.EOFException: No content to map to Object due to end of input
    at org.codehaus.jackson.map.ObjectMapper._initForReading(ObjectMapper.java:2173)
    at org.codehaus.jackson.map.ObjectMapper._readValue(ObjectMapper.java:2106)
    at org.codehaus.jackson.map.ObjectMapper.readTree(ObjectMapper.java:1065)
    at org.codehaus.jackson.map.ObjectMapper.readTree(ObjectMapper.java:1040)
    at org.apache.avro.Schema.parse(Schema.java:895)

除非您的环境设置正确，否则从“资源”中读取文件充满了问题。此外，由于您之前提到它曾经工作过，您可能只是更改了一些环境设置（例如工作目录）以进行第二次运行。

尝试将模式字符串复制粘贴到 String 变量中并直接解析它，而不是使用资源加载器：

String schemaJson = "paste schema here (and fix quotes)";
Schema schema = Schema.parse(schemaJson);
GenericRecord datum = new GenericData.Record(schema);
...
于 2011-09-05T03:26:52.290 回答
1 
    GenericRecord result=dataFileReader.next();
    System.out.println("data" + result.get("left").toString());
    result=dataFileReader.next();
    System.out.println("data :" + result.get("left").toString());

我想这就是你出错的地方。

您应该调用记录的“左”属性和“右”属性。

试试看。

它对我有用。

于 2012-05-22T11:43:29.287 回答
0

如果文件位于 jar 的根目录上，则在文件名前放置一个斜杠。

Schema.parse(getClass().getResourceAsStream("/Pair.avsc"));
于 2014-11-15T21:25:44.650 回答