I am building a MapR-ES Java producer, that connects to Oracle via JDBC and gets a result set back to be published into a stream.
I want to serialize my populated class object into an Avro string to be the message of my publisher.
I have used the Maven Apache Avro plugin to generate an Avro string for my class object with
Schema schema = ReflectionData.get().getSchema(MyClass.class);
But, if i have a fully populated MyClass Object, how to i generate an Avro string with the schema and populated data?
I havent found any good examples on this. Any help is appreciated.
Let's say if i have ReflectedCustomer class in java.
import org.apache.avro.reflect.Nullable;
public class ReflectedCustomer {
private String firstName;
private String lastName;
@Nullable private String nickName;
// needed by the reflection
public ReflectedCustomer(){}
public ReflectedCustomer(String firstName, String lastName, String nickName) {
this.firstName = firstName;
this.lastName = lastName;
this.nickName = nickName;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String fullName(){
return this.firstName + " " + this.lastName + " " + this.nickName;
}
public String getNickName() {
return nickName;
}
public void setNickName(String nickName) {
this.nickName = nickName;
}
}
Below code will use the above ReflectedCustomer and generate the Avro String and it will read it back.
import org.apache.avro.Schema;
import org.apache.avro.file.CodecFactory;
import org.apache.avro.file.DataFileReader;
import org.apache.avro.file.DataFileWriter;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.DatumWriter;
import org.apache.avro.reflect.ReflectData;
import org.apache.avro.reflect.ReflectDatumReader;
import org.apache.avro.reflect.ReflectDatumWriter;
import java.io.File;
import java.io.IOException;
public class ReflectionExamples {
public static void main(String[] args) {
// here we use reflection to determine the schema
Schema schema = ReflectData.get().getSchema(ReflectedCustomer.class);
System.out.println("schema = " + schema.toString(true));
// create a file of ReflectedCustomers
try {
System.out.println("Writing customer-reflected.avro");
File file = new File("customer-reflected.avro");
DatumWriter<ReflectedCustomer> writer = new ReflectDatumWriter<>(ReflectedCustomer.class);
DataFileWriter<ReflectedCustomer> out = new DataFileWriter<>(writer)
.setCodec(CodecFactory.deflateCodec(9))
.create(schema, file);
out.append(new ReflectedCustomer("Bill", "Clark", "The Rocket"));
out.close();
} catch (IOException e) {
e.printStackTrace();
}
// read from an avro into our Reflected class
// open a file of ReflectedCustomers
try {
System.out.println("Reading customer-reflected.avro");
File file = new File("customer-reflected.avro");
DatumReader<ReflectedCustomer> reader = new ReflectDatumReader<>(ReflectedCustomer.class);
DataFileReader<ReflectedCustomer> in = new DataFileReader<>(file, reader);
// read ReflectedCustomers from the file & print them as JSON
for (ReflectedCustomer reflectedCustomer : in) {
System.out.println(reflectedCustomer.fullName());
}
// close the input file
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}