Avro序列化Java中 的BigDecimal

背景

由于业务需要，需要将SparkSQL中Array、Map、Struct使用avro序列化成一个大的字节数组进行存储。但是在序列化过程中，涉及到Java的BigDecimal类型，根据avro官网提示，定义schema如下：

{
    "namespace":"com.bugboy.avro.bean",
    "type":"record",
    "name":"DecimalDemo",
    "fields":[
        {"name":"id", "type":"string"},
        {"name":"value","type":{"type":"bytes","logicalType": "decimal","precision": 10,"scale": 2}}
    ]
}

使用该schema序列化时，还是遇到了很多问题，比如java.math.BigDecimal不能强转成ByteBuffer等等，这里就不细说了。反正就是官网上没有找到具体实现方案。

方案

也许源码中会有对应的demo，但由于时间紧迫，没办法自己看源码，就使用面对debug编程的笨办法一步一步的设置，摸索。在经过多次尝试之后，最终得到如下方案进行对包含有BigDecimal的Record（对应SparkSQL中的Struct）进行序列化与反序列化。

package com.bugboy.avro.bean;

import org.apache.avro.Conversions;
import org.apache.avro.LogicalTypes;
import org.apache.avro.Schema;
import org.apache.avro.SchemaBuilder;
import org.apache.avro.generic.GenericData;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericDatumWriter;
import org.apache.avro.io.BinaryDecoder;
import org.apache.avro.io.BinaryEncoder;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.io.EncoderFactory;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.math.BigDecimal;

public class SerRecord {
  public static void main(String[] args) throws IOException {
    // 构建record的schema，当然，也可以使用解析器解析定义好的json直接生成schema
    SchemaBuilder.BaseTypeBuilder<Schema> builder = SchemaBuilder.builder();
    SchemaBuilder.FieldAssembler<Schema> fieldAssembler = builder.record("Hello").namespace("").fields();
    fieldAssembler.name("id")
            .type(builder.stringType())
            .noDefault();
    Schema decimalSchema = builder.bytesType();
    LogicalTypes.decimal(10, 2).addToSchema(decimalSchema);
    fieldAssembler.name("value")
            .type(decimalSchema)
            .noDefault();
    Schema schema = fieldAssembler.endRecord(); // 构建结束

    // 准备好Record
    GenericData.Record record = new GenericData.Record(schema);
    record.put("id", "001");
    record.put("value", BigDecimal.valueOf(67.78));

    // 序列化
    GenericDatumWriter<GenericData.Record> writer = new GenericDatumWriter<>();
    // 需要设置DecimalConversion序列化器，否则会报BigDecimal不能强转ByteBuffer的异常。
    writer.getData().addLogicalTypeConversion(new Conversions.DecimalConversion());
    // 需要进行设置，否则会空指针异常
    writer.setSchema(schema);
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    BinaryEncoder encoder = EncoderFactory.get().directBinaryEncoder(baos, null);
    // 进行序列化，得到字节数组
    writer.write(record, encoder);
    byte[] bytes = baos.toByteArray();

    // 进行反序列化，将字节数组转化成Record
    GenericDatumReader<GenericData.Record> reader = new GenericDatumReader<>();
    ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
    BinaryDecoder decoder = DecoderFactory.get().directBinaryDecoder(bais, null);
    // 设置schema，否则会报空指针异常
    reader.setExpected(schema);
    reader.setSchema(schema);
    // 反序列化
    GenericData.Record newRecord = reader.read(null, decoder);
    // 取值进行验证
    System.out.println(newRecord.get("id"));
    System.out.println(newRecord.get("value"));
  }
}

pom依赖如下：

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>

    <groupId>com.bugboygroupId>
    <artifactId>avro-bean-serderartifactId>
    <version>1.0.0version>
    <properties>
        <avro-version>1.8.2avro-version>
    properties>
    <dependencies>
        <dependency>
            <groupId>org.apache.avrogroupId>
            <artifactId>avroartifactId>
            <version>${avro-version}version>
        dependency>
        <dependency>
            <groupId>joda-timegroupId>
            <artifactId>joda-timeartifactId>
            <version>2.9.4version>
        dependency>
    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.pluginsgroupId>
                <artifactId>maven-compiler-pluginartifactId>
                <configuration>
                    <source>1.8source>
                    <target>1.8target>
                configuration>
            plugin>

            <plugin>
                <groupId>org.apache.avrogroupId>
                <artifactId>avro-maven-pluginartifactId>
                <version>${avro-version}version>
                <executions>
                    <execution>
                        <phase>generate-sourcesphase>
                        <goals>
                            <goal>schemagoal>
                        goals>
                        <configuration>
                            <sourceDirectory>${project.basedir}/src/main/avro/sourceDirectory>
                            <outputDirectory>${project.basedir}/src/main/java/outputDirectory>
                        configuration>
                    execution>
                executions>
            plugin>

        plugins>
    build>
project>

写在最后

过年不能回家，好烦啊！！！！！