从Java对象创建Avro字符串

Posted 2021-04-21

我正在构建一个MapR-ES Java生成器，它通过JDBC连接到Oracle并获取结果集以发布到流中。

我想将我填充的类对象序列化为Avro字符串，作为我的发布者的消息。

我使用Maven Apache Avro插件为我的类对象生成一个Avro字符串

Schema schema = ReflectionData.get().getSchema(MyClass.class);

但是，如果我有一个完全填充的MyClass对象，如何生成带有架构和填充数据的Avro字符串？

我还没有找到任何好的例子。任何帮助表示赞赏。

答案

假设我在java中有ReflectedCustomer类。

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;
}
}

下面的代码将使用上面的ReflectedCustomer并生成Avro String，它将读回来。

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();
        }



    }
}