Java Avro向后模式演化引发ClassCastException
当我试图用一个简单的Java程序测试Avro模式演化时,我得到了一个Java Avro向后模式演化引发ClassCastException,java,apache-kafka,avro,Java,Apache Kafka,Avro,当我试图用一个简单的Java程序测试Avro模式演化时,我得到了一个ClassCastException Avro版本:1.10.0 customer-v1.avsc { "type": "record", "namespace": "com.practice.kafka", "name": "Customer", "doc": "
ClassCastException
Avro版本:1.10.0
customer-v1.avsc
{
"type": "record",
"namespace": "com.practice.kafka",
"name": "Customer",
"doc": "Avro schema for Customer",
"fields": [
{"name": "first_name", "type": "string", "doc": "Customer first name"},
{"name": "last_name", "type": "string", "doc": "Customer last name"},
{"name": "automated_email", "type": "boolean", "default": true, "doc": "Receive marketing emails or not"}
]
}
{
"type": "record",
"namespace": "com.practice.kafka",
"name": "CustomerV2",
"doc": "Avro schema for Customer",
"fields": [
{"name": "first_name", "type": "string", "doc": "Customer first name"},
{"name": "last_name", "type": "string", "doc": "Customer last name"},
{"name": "phone_number", "type": ["null","boolean"], "default": null, "doc": "Optional phone number"},
{"name": "email", "type": "string", "default": "missing@example.com", "doc": "Optional email address"}
]
}
customer-v2.avsc
{
"type": "record",
"namespace": "com.practice.kafka",
"name": "Customer",
"doc": "Avro schema for Customer",
"fields": [
{"name": "first_name", "type": "string", "doc": "Customer first name"},
{"name": "last_name", "type": "string", "doc": "Customer last name"},
{"name": "automated_email", "type": "boolean", "default": true, "doc": "Receive marketing emails or not"}
]
}
{
"type": "record",
"namespace": "com.practice.kafka",
"name": "CustomerV2",
"doc": "Avro schema for Customer",
"fields": [
{"name": "first_name", "type": "string", "doc": "Customer first name"},
{"name": "last_name", "type": "string", "doc": "Customer last name"},
{"name": "phone_number", "type": ["null","boolean"], "default": null, "doc": "Optional phone number"},
{"name": "email", "type": "string", "default": "missing@example.com", "doc": "Optional email address"}
]
}
序列化v1和反序列化v2的程序
package com.practice.kafka;
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.specific.SpecificDatumReader;
import org.apache.avro.specific.SpecificDatumWriter;
import java.io.File;
import java.io.IOException;
public class BackwardSchemaEvolutionSample {
public static void main(String[] args) {
// Step 1 - Create specific record
Customer customer = Customer.newBuilder().setFirstName("John").setLastName("Doe").setAutomatedEmail(false).build();
// Step 2 - Write specific record to a file
final DatumWriter<Customer> datumWriter = new SpecificDatumWriter<>();
try (DataFileWriter<Customer> dataFileWriter = new DataFileWriter<>(datumWriter)) {
dataFileWriter.create(customer.getSchema(), new File("customer-v1.avro"));
dataFileWriter.append(customer);
} catch (IOException e) {
e.printStackTrace();
}
// Step 3 - Read specific record from a file
final File file = new File("customer-v1.avro");
final DatumReader<CustomerV2> datumReader = new SpecificDatumReader<>();
CustomerV2 customerRecord;
try (DataFileReader<CustomerV2> dataFileReader = new DataFileReader<>(file, datumReader)) {
customerRecord = dataFileReader.next();
System.out.println(customerRecord.toString());
} catch (IOException e) {
e.printStackTrace();
}
}
}
您能告诉我如何修复此错误吗?您定义了两种数据类型
Customer
和Customer2
,并且您不能进行任何转换,因为它们没有继承关系。
所以Java不能进行强制转换,而您得到的是ClassCastException
。
在您的代码中,唯一的解决方案是捕获ClassCastException
,并在catch块中将Customer转换为Customer2
我假设您正在Kafka环境中模拟模式的更改。
在此场景中,您将通过添加新字段或删除旧字段来扩展现有的avro模式
只要类的名称保持不变,avro模式的更改就会起作用