Produce Avro messages with the schema registry

Set up an Apache Maven project

1. Connect to the client VM using SSH. One way to do this is to run the following command:

    gcloud  
   compute  
   ssh  
   --project = 
    PROJECT_ID 
     
    \ 
   --zone = 
    REGION 
   -f  
   test-instance 
   

   For more information about connecting using SSH, see About SSH connections .

2. Install Java and Maven with the command:

    sudo  
   apt-get  
   install  
   maven  
   openjdk-17-jdk 
   

3. Set up an Apache Maven project.

   Use the following command to create a package com.google.example in a directory called demo .

    mvn  
   archetype:generate  
   -DartifactId = 
   demo  
   -DgroupId = 
   com.google.example \ 
     
   -DarchetypeArtifactId = 
   maven-archetype-quickstart \ 
     
   -DarchetypeVersion = 
    1 
   .5  
   -DinteractiveMode = 
    false 
    
   

Define the schema and its Java implementation

In this example, a message represents a "user" that has a name and an optional ID. The corresponds to an Avro schema with two fields: a required field name of type string and an optional integer id. To use this schema in a Java program, you will also need to generate an Java implementation of an object corresponding to this schema.

1. Change into the project directory with cd demo .

2. Create the folders for storing schema files in your code:

    mkdir  
   -p  
   src/main/avro 
   

3. Create the Avro schema definition by pasting the following code into a file called src/main/avro/User.avsc :

     { 
     
    "namespace" 
    : 
     
    "com.google.example" 
    , 
     
    "type" 
    : 
     
    "record" 
    , 
     
    "name" 
    : 
     
    "User" 
    , 
     
    "fields" 
    : 
     
    [ 
     
    { 
    "name" 
    : 
     
    "name" 
    , 
     
    "type" 
    : 
     
    "string" 
    }, 
     
    { 
    "name" 
    : 
     
    "id" 
    , 
     
    "type" 
    : 
     
    [ 
    "int" 
    , 
     
    "null" 
    ]} 
     
    ] 
    } 
    
   

4. Configure your Maven project to use an Avro Java code generation plugin by adding the following to the build node of your pom.xml. Note that the pom.xml may have other plugins nodes inside the pluginManagement node. Don't change the pluginManagement node in this step. The plugins node needs to be at the same level level as pluginManagement .

    <plugins>
   <plugin>  
   <groupId>org.apache.avro</groupId>  
   <artifactId>avro-maven-plugin</artifactId>  
   <version>1.11.1</version>  
   <executions>  
   <execution>  
   <phase>generate-sources</phase>  
   <goals>  
   <goal>schema</goal>  
   </goals>  
   <configuration>  
   <sourceDirectory>${project.basedir}/src/main/avro/</sourceDirectory>  
   <outputDirectory>${project.basedir}/src/main/java/</outputDirectory>  
   </configuration>  
   </execution>  
   </executions>
   </plugin>
   </plugins> 
   

5. Add Avro as a dependency by adding the following to the end of the project/dependencies node of pom.xml . Note that the pom.xml already has a dependencies node inside dependencyManagement tag. Don't change the dependncyManagement node in this step.

    <dependency>  
   <groupId>org.apache.avro</groupId>  
   <artifactId>avro</artifactId>  
   <version>1.11.1</version>
   </dependency> 
   

6. Generate Java sources

      
   mvn  
   generate-sources 
   

7. Run the following command to check that the implementation source file was created. The source is a Java class file that implements constructors, accessors, serializers and de-serializers for User objects. You will use this class in the producer code.

    cat  
   src/main/java/com/google/example/User.java 
   

Create a producer client

This section walks through the steps of writing, building, and running a producer client.

Implement the producer

The producer uses KafkaAvroSerializer.java to encode messages and manage their schemas. The serializer automatically connects to the schema registry, registers the schema under a subject, retrieves its ID, and then serializes the message using Avro. You still need to configure the producer and serializer.

1. Create the producer client class by pasting the following code into a new file called src/main/java/com/google/example/UserProducer.java

     package 
     
    com.google.example 
    ; 
    import 
     
    java.util.Properties 
    ; 
    import 
     
    org.apache.kafka.clients.producer.KafkaProducer 
    ; 
    import 
     
    org.apache.kafka.clients.producer.ProducerRecord 
    ; 
    import 
     
    org.apache.kafka.clients.producer.RecordMetadata 
    ; 
    import 
     
    org.apache.kafka.clients.producer.ProducerConfig 
    ; 
    import 
     
    org.apache.kafka.common.serialization.StringSerializer 
    ; 
    import 
     
    io.confluent.kafka.serializers.KafkaAvroSerializer 
    ; 
     
    public 
     
    class 
    UserProducer 
     
    { 
     
    private 
     
    static 
     
    Properties 
     
    configure 
    () 
     
    throws 
     
    Exception 
     
    { 
     
    Properties 
     
    p 
     
    = 
     
    new 
     
    Properties 
    (); 
     
    p 
    . 
    load 
    ( 
    new 
     
    java 
    . 
    io 
    . 
    FileReader 
    ( 
    "client.properties" 
    )); 
     
    p 
    . 
    put 
    ( 
    ProducerConfig 
    . 
    KEY_SERIALIZER_CLASS_CONFIG 
    , 
     
    StringSerializer 
    . 
    class 
    ); 
     
    p 
    . 
    put 
    ( 
    ProducerConfig 
    . 
    VALUE_SERIALIZER_CLASS_CONFIG 
    , 
     
    KafkaAvroSerializer 
    . 
    class 
    ); 
     
    return 
     
    p 
    ; 
     
    } 
     
    public 
     
    static 
     
    void 
     
    main 
    ( 
    String 
    [] 
     
    args 
    ) 
     
    throws 
     
    Exception 
     
    { 
     
    Properties 
     
    p 
     
    = 
     
    configure 
    (); 
     
    KafkaProducer<String 
    , 
     
    User 
   >  
    producer 
     
    = 
     
    new 
     
    KafkaProducer<String 
    , 
     
    User 
   > ( 
    p 
    ); 
     
    final 
     
    User 
     
    u 
     
    = 
     
    new 
     
    User 
    ( 
    "SchemaEnthusiast" 
    , 
     
    42 
    ); 
     
    final 
     
    String 
     
    topicName 
     
    = 
     
    "newUsers" 
    ; 
     
    ProducerRecord<String 
    , 
     
    User 
   >  
    message 
     
    = 
     
    new 
     
    ProducerRecord<String 
    , 
     
    User 
   > ( 
    topicName 
    , 
     
    "" 
    , 
     
    u 
    ); 
     
    producer 
    . 
    send 
    ( 
    message 
    , 
     
    new 
     
    SendCallback 
    ()); 
     
    producer 
    . 
    close 
    (); 
     
    } 
     
    } 
    
   

2. Define the callback class in src/main/java/com/google/example/SendCallback.java :

     package 
     
    com.google.example 
    ; 
    import 
     
    org.apache.kafka.clients.producer.Callback 
    ; 
    import 
     
    org.apache.kafka.clients.producer.RecordMetadata 
    ; 
    class 
    SendCallback 
     
    implements 
     
    Callback 
     
    { 
     
    public 
     
    void 
     
    onCompletion 
    ( 
    RecordMetadata 
     
    m 
    , 
     
    Exception 
     
    e 
    ){ 
     
    if 
     
    ( 
    e 
     
    == 
     
    null 
    ){ 
     
    System 
    . 
    out 
    . 
    println 
    ( 
    "Produced a message successfully." 
    ); 
     
    } 
     
    else 
     
    { 
     
    System 
    . 
    out 
    . 
    println 
    ( 
    e 
    . 
    getMessage 
    ()); 
     
    } 
     
    } 
    } 
    
   

3. To compile this code, you need the org.apache.kafka.clients package and the serializer code. The serializer Maven artifact is distributed through a custom repository. Add the following node to the project node of your pom.xml to configure this repository:

      
   <repositories>  
   <repository>  
   <id>confluent</id>  
   <name>Confluent</name>  
   <url>https://packages.confluent.io/maven/</url>  
   </repository>  
   </repositories> 
   

4. Add the following to the dependencies node in your pom.xml file:

      
   <dependency>  
   <groupId>org.slf4j</groupId>  
   <artifactId>slf4j-simple</artifactId>  
   <version>1.7.32</version>  
   </dependency>  
   <dependency>  
   <groupId>io.confluent</groupId>  
   <artifactId>kafka-avro-serializer</artifactId>  
   <version>7.8.1</version>  
   </dependency>  
   <dependency>  
   <groupId>org.apache.kafka</groupId>  
   <artifactId>kafka-clients</artifactId>  
   <version>3.7.2</version>  
   </dependency> 
   

5. To make sure all the dependencies are properly resolved, compile the client:

    mvn  
   compile 
   

Create a schema registry

To create a schema registry, run the following command:

 gcloud  
beta  
managed-kafka  
schema-registries  
create  
 REGISTRY_ID 
  
 \ 
  
--location = 
 REGION 
 

Replace the following:

• REGISTRY_ID : a unique identifier for your new schema registry. This forms part of the registry's resource name. The name must start with a letter, contain only letters (a-z, A-Z) , numbers (0-9) , and underscores (_) , and be 63 characters or less.

• REGION : Google Cloud region where the schema registry is going to be created. This location must match the region of the Kafka cluster or clusters using this registry.

The schema definition that you have created is not yet uploaded to the registry. The producer client does this the first time it runs in the following steps.

Configure and run the producer

At this point the producer won't run since it is not fully configured. To configure the producer, provide both the Kafka and schema registry configuration.

1. Create a file called client.properties in the same directory as your pom.xml and add the following content to it:

    bootstrap.servers=bootstrap. CLUSTER_ID 
   . REGION 
   .managedkafka. PROJECT_ID 
   .cloud.goog:9092
   
   security.protocol=SASL_SSL
   sasl.mechanism=OAUTHBEARER
   sasl.login.callback.handler.class=com.google.cloud.hosted.kafka.auth.GcpLoginCallbackHandler
   sasl.jaas.config=org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required;
   
   schema.registry.url=https://managedkafka.googleapis.com/v1/projects/ PROJECT_ID 
   /locations/ REGION 
   /schemaRegistries/ REGISTRY_ID 
   bearer.auth.credentials.source=CUSTOM
   bearer.auth.custom.provider.class=com.google.cloud.hosted.kafka.auth.GcpBearerAuthCredentialProvider 
   

   Add the Kafka and schema registry authentication handler dependencies to your Maven project by inserting the following to the dependencies node of pom.xml above the kafka-avro-serializer dependency:

      
   <dependency>  
   <groupId>com.google.cloud.hosted.kafka</groupId>  
   <artifactId>managed-kafka-auth-login-handler</artifactId>  
   <version>1.0.6</version>  
   <exclusions>  
   <exclusion>  
   <groupId>io.confluent</groupId>  
   <artifactId>kafka-schema-registry-client</artifactId>  
   </exclusion>  
   </exclusions>  
   </dependency> 
   

   If you would like to see the implementation of the custom schema registry authentcation handler authentication handler, look at the GcpBearerAuthCredentialProvider class.

2. Compile and run the producer client:

    mvn  
   compile  
   -q  
   exec:java  
   -Dexec.mainClass = 
   com.google.example.UserProducer 
   

   If all goes well, you see the output Produced a message successfully generated by the SendCallback class.

Examine the output

1. Check that the User schema has been registered under a subject name derived from the topic and schema names:

     SR_DOMAIN 
    = 
   https://managedkafka.googleapis.com SR_PATH 
    = 
   /v1/projects/ PROJECT_ID 
   /locations/ REGION 
    SR_HOST 
    = 
    $SR_DOMAIN 
   / $SR_PATH 
   /schemaRegistries/ REGISTRY_ID 
   /subjects
   
   curl  
   -X  
   GET  
    \ 
     
   -H  
    "Content-Type: application/vnd.schemaregistry.v1+json" 
     
    \ 
     
   -H  
    "Authorization: Bearer 
    $( 
   gcloud  
   auth  
   print-access-token ) 
    " 
    \ 
     
    $SR_HOST 
    
   

   The output of this command should look like this:

    ["newUsers-value"] 
   

2. Check that the schema registered in the repository is the same as User :

    curl  
   -X  
   GET  
    \ 
     
   -H  
    "Content-Type: application/vnd.schemaregistry.v1+json" 
     
    \ 
     
   -H  
    "Authorization: Bearer 
    $( 
   gcloud  
   auth  
   print-access-token ) 
    " 
     
    \ 
     
    $SR_HOST 
   /newUsers-value/versions/1 
   

   The output of the command should look like this:

    {
     "subject": "newUsers-value",
     "version": 1,
     "id": 2,
     "schemaType": "AVRO",
     "schema": "{\"type\":\"record\",\"name\":\"User\",\"namespace\":\"com.google.example\",\"fields\":[{\"name\":\"name\",\"type\":\"string\"},{\"name\":\"id\",\"type\":[\"int\",\"null\"]}]}",
     "references": []
   }