序列化
kafka自带的序列化器都实现了org.apache.kafka.common.serialization.Serializer接口
该类如下：
package org.apache.kafka.common.serialization;
import java.io.Closeable;
import java.util.Map;
/**
* An interface for converting objects to bytes.
*
* A class that implements this interface is expected to have a constructor with no parameter.
* <p>
* Implement {@link org.apache.kafka.common.ClusterResourceListener} to receive cluster metadata once it's available. Please see the class documentation for ClusterResourceListener for more information.
*
* @param <T> Type to be serialized from.
*/
public interface Serializer<T> extends Closeable {
/**
* Configure this class.
* @param configs configs in key/value pairs
* @param isKey whether is for key or value
*/
void configure(Map<String, ?> configs, boolean isKey);
/**
* Convert {@code data} into a byte array.
*
* @param topic topic associated with data
* @param data typed data
* @return serialized bytes
*/
byte[] serialize(String topic, T data);
/**
* Close this serializer.
*
* This method must be idempotent as it may be called multiple times.
*/
@Override
void close();
}
方法直观明了，不再解释。
其继承结构如下：
序列化继承结构.jpg
- 其中：org.apache.kafka.common.serialization.StringSerializer源码如下：
package org.apache.kafka.common.serialization;
import org.apache.kafka.common.errors.SerializationException;
import java.io.UnsupportedEncodingException;
import java.util.Map;
/**
* String encoding defaults to UTF8 and can be customized by setting the property key.serializer.encoding,
* value.serializer.encoding or serializer.encoding. The first two take precedence over the last.
*/
public class StringSerializer implements Serializer<String> {
private String encoding = "UTF8";
@Override
public void configure(Map<String, ?> configs, boolean isKey) {
String propertyName = isKey ? "key.serializer.encoding" : "value.serializer.encoding";
Object encodingValue = configs.get(propertyName);
if (encodingValue == null)
encodingValue = configs.get("serializer.encoding");
if (encodingValue instanceof String)
encoding = (String) encodingValue;
}
@Override
public byte[] serialize(String topic, String data) {
try {
if (data == null)
return null;
else
return data.getBytes(encoding);
} catch (UnsupportedEncodingException e) {
throw new SerializationException("Error when serializing string to byte[] due to unsupported encoding " + encoding);
}
}
@Override
public void close() {
// nothing to do
}
}
方法直观明了，不再解释。
实体类定义如下：
package com.ghq.kafka.entity;
public class Company {
private String name;
private String address;
public Company(){}
public Company(String name, String address) {
this.name = name;
this.address = address;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "Company{" +
"name='" + name + '\'' +
", address='" + address + '\'' +
'}';
}
}
序列化器定义如下（实现Serializer接口即可）：
package com.ghq.kafka.server;
import com.ghq.kafka.entity.Company;
import org.apache.kafka.common.serialization.Serializer;
import java.nio.ByteBuffer;
import java.util.Map;
public class CompanySerializer implements Serializer<Company> {
@Override
public void configure(Map<String, ?> configs, boolean isKey) {
}
@Override
public byte[] serialize(String topic, Company data) {
if (data == null) {
return null;
}
byte[] name,address;
try{
if(data.getName() != null){
name = data.getName().getBytes("UTF-8");
}else {
name = new byte[0];
}
if(data.getAddress() != null){
address = data.getAddress().getBytes("UTF-8");
}else{
address = new byte[0];
}
ByteBuffer buffer = ByteBuffer.allocate(4 + 4 + name.length + address.length);
buffer.putInt(name.length);
buffer.put(name);
buffer.putInt(address.length);
buffer.put(address);
return buffer.array();
}catch (Exception e){
e.printStackTrace();
}
return new byte[0];
}
@Override
public void close() {
}
}
主方法实现逻辑如下：
package com.ghq.kafka.server;
import com.ghq.kafka.entity.Company;
import org.apache.kafka.clients.producer.*;
import java.util.Properties;
public class CompanyProducerDemo {
public static final String brokerList = "192.168.52.135:9092";
public static final String topic = "company-demo";
public static Properties initProperties(){
Properties prop = new Properties();
//这里将key.serializer 定义为我们自定义的CompanySerializer
prop.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, CompanySerializer.class.getName());
////这里将value.serializer 定义为我们自定义的CompanySerializer
prop.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, CompanySerializer.class.getName());
prop.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, brokerList);
prop.put(ProducerConfig.CLIENT_ID_CONFIG,"company.client.id.demo");
prop.put(ProducerConfig.RETRIES_CONFIG,10);
return prop;
}
public static void main(String[] args) {
async();
}
public static void async() {
Properties prop = initProperties();
//注意泛型
KafkaProducer<String, Company> producer = new KafkaProducer<>(prop);
Company company = new Company("xxxxxxxx","yyyyyyyyyy");
ProducerRecord<String, Company> record = new ProducerRecord<>(topic, company);
producer.send(record, new Callback() {
/**
* metadata 和 exception 互斥
* 消息发送成功：metadata != null exception == null
* 消息发送失败：metadata == null exception != null
*/
@Override
public void onCompletion(RecordMetadata metadata, Exception exception) {
if (exception != null) {
System.out.println("消息1发送失败："+metadata);
}else {
System.out.println("消息1发送成功："+metadata);
}
}
});
producer.send(record, (metadata, exception) -> {
if (exception != null) {
System.out.println("消息2发送失败："+metadata);
}else {
System.out.println("消息2发送成功："+metadata);
}
});
producer.close();
}
}
反序列化
kafka自带的反序列化器都实现了org.apache.kafka.common.serialization.Deserializer接口
该类如下：
public interface Deserializer<T> extends Closeable {
/**
* Configure this class.
* @param configs configs in key/value pairs
* @param isKey whether is for key or value
*/
void configure(Map<String, ?> configs, boolean isKey);
/**
* Deserialize a record value from a byte array into a value or object.
* @param topic topic associated with the data
* @param data serialized bytes; may be null; implementations are recommended to handle null by returning a value or null rather than throwing an exception.
* @return deserialized typed data; may be null
*/
T deserialize(String topic, byte[] data);
@Override
void close();
其继承结构如下：
反序列化继承结构.png
- 其中：org.apache.kafka.common.serialization.StringDeserializer 类如下：
import java.io.UnsupportedEncodingException;
import java.util.Map;
/**
* String encoding defaults to UTF8 and can be customized by setting the property key.deserializer.encoding,
* value.deserializer.encoding or deserializer.encoding. The first two take precedence over the last.
*/
public class StringDeserializer implements Deserializer<String> {
private String encoding = "UTF8";
@Override
public void configure(Map<String, ?> configs, boolean isKey) {
String propertyName = isKey ? "key.deserializer.encoding" : "value.deserializer.encoding";
Object encodingValue = configs.get(propertyName);
if (encodingValue == null)
encodingValue = configs.get("deserializer.encoding");
if (encodingValue instanceof String)
encoding = (String) encodingValue;
}
@Override
public String deserialize(String topic, byte[] data) {
try {
if (data == null)
return null;
else
return new String(data, encoding);
} catch (UnsupportedEncodingException e) {
throw new SerializationException("Error when deserializing byte[] to string due to unsupported encoding " + encoding);
}
}
@Override
public void close() {
// nothing to do
}
}
自定义的反序列化器如下(和上文的序列化器对应)：
package com.ghq.kafka.client;
import com.ghq.kafka.entity.Company;
import org.apache.kafka.common.errors.SerializationException;
import org.apache.kafka.common.serialization.Deserializer;
import java.nio.ByteBuffer;
import java.util.Map;
public class CompanyDeserializer implements Deserializer<Company> {
@Override
public void configure(Map<String, ?> configs, boolean isKey) {
}
@Override
public Company deserialize(String topic, byte[] data) {
if (data == null) {
return null;
}
if (data.length < 8) {
throw new SerializationException("序列化失败...");
}
ByteBuffer buffer = ByteBuffer.wrap(data);
int nameLength, addressLength;
String name = null, address = null;
nameLength = buffer.getInt();
byte[] nameBytes = new byte[nameLength];
buffer.get(nameBytes);
addressLength = buffer.getInt();
byte[] addressBytes = new byte[addressLength];
buffer.get(addressBytes);
try {
name = new String(nameBytes, "UTF-8");
address = new String(addressBytes, "UTF-8");
} catch (Exception e) {
e.printStackTrace();
}
return new Company(name, address);
}
@Override
public void close() {
}
}
消费者客户端编写：
package com.ghq.kafka.client;
import com.ghq.kafka.entity.Company;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import java.time.Duration;
import java.util.Collections;
import java.util.Properties;
public class CompanyConsumerDemo {
public static final String brokerList = "192.168.52.135:9092";
public static final String topic = "company-demo";
public static final String groupId = "group.demo";
public static Properties initProperties(){
Properties prop = new Properties();
//这里将key.deserializer 定义为我们自定义的CompanyDeserializer
prop.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, CompanyDeserializer.class.getName());
//这里将value.deserializer 定义为我们自定义的CompanyDeserializer
prop.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, CompanyDeserializer.class.getName());
prop.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, brokerList);
prop.put(ConsumerConfig.GROUP_ID_CONFIG, groupId);
prop.put(ConsumerConfig.CLIENT_ID_CONFIG, "company-id-demo");
return prop;
}
public static void main(String[] args) {
Properties prop = initProperties();
KafkaConsumer<String, Company> consumer = new KafkaConsumer<>(prop);
consumer.subscribe(Collections.singletonList(topic));
while (true) {
ConsumerRecords<String, Company> records = consumer.poll(Duration.ofSeconds(5));
for (ConsumerRecord<String, Company> record : records) {
System.out.println("--------------->:" + record.value());
}
}
}
}
分别执行生产者和消费者客户端，结果如下：
消息1发送成功：company-demo-0@4
消息2发送成功：company-demo-0@5
--------------->:Company{name='xxxxxxxx', address='yyyyyyyyyy'}
--------------->:Company{name='xxxxxxxx', address='yyyyyyyyyy'}
结束。
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