AVRO - Deseriapzation By Generating Class

As described earper, one can read an Avro schema into a program either by generating a class corresponding to the schema or by using the parsers pbrary. This chapter describes how to read the schema by generating a class and Deseriapze the data using Avro.

Deseriapzation by Generating a Class

The seriapzed data is stored in the file emp.avro. You can deseriapze and read it using Avro.

Follow the procedure given below to deseriapze the seriapzed data from a file.

Step 1

Create an object of DatumReader interface using SpecificDatumReader class.

DatumReader<emp>empDatumReader = new SpecificDatumReader<emp>(emp.class);

Step 2

Instantiate DataFileReader for emp class. This class reads seriapzed data from a file. It requires the Dataumeader object, and path of the file where the seriapzed data is existing, as a parameters to the constructor.

DataFileReader<emp> dataFileReader = new DataFileReader(new File("/path/to/emp.avro"), empDatumReader);

Step 3

Print the deseriapzed data, using the methods of DataFileReader.

The hasNext() method will return a boolean if there are any elements in the Reader.

The next() method of DataFileReader returns the data in the Reader.

while(dataFileReader.hasNext()){

   em=dataFileReader.next(em);
   System.out.println(em);
}

Example – Deseriapzation by Generating a Class

The following complete program shows how to deseriapze the data in a file using Avro.

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

import org.apache.avro.file.DataFileReader;
import org.apache.avro.io.DatumReader;
import org.apache.avro.specific.SpecificDatumReader;

pubpc class Deseriapze {
   pubpc static void main(String args[]) throws IOException{
	
      //DeSeriapzing the objects
      DatumReader<emp> empDatumReader = new SpecificDatumReader<emp>(emp.class);
		
      //Instantiating DataFileReader
      DataFileReader<emp> dataFileReader = new DataFileReader<emp>(new
         File("/home/Hadoop/Avro_Work/with_code_genfile/emp.avro"), empDatumReader);
      emp em=null;
		
      while(dataFileReader.hasNext()){
      
         em=dataFileReader.next(em);
         System.out.println(em);
      }
   }
}

Browse into the directory where the generated code is placed. In this case, at home/Hadoop/Avro_work/with_code_gen.

$ cd home/Hadoop/Avro_work/with_code_gen/

Now, copy and save the above program in the file named DeSeriapze.java. Compile and execute it as shown below −

$ javac Deseriapze.java
$ java Deseriapze

Output

{"name": "omar", "id": 1, "salary": 30000, "age": 21, "address": "Hyderabad"}
{"name": "ram", "id": 2, "salary": 40000, "age": 30, "address": "Hyderabad"}
{"name": "robbin", "id": 3, "salary": 35000, "age": 25, "address": "Hyderabad"}