Chapter 20. Avro DataFormat

Available as of Camel version 2.14

This component provides a dataformat for avro, which allows serialization and deserialization of messages using Apache Avro’s binary dataformat. Moreover, it provides support for Apache Avro’s rpc, by providing producers and consumers endpoint for using avro over netty or http.

Maven users will need to add the following dependency to their pom.xml for this component: 

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-avro</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

20.1. Apache Avro Overview

Avro allows you to define message types and a protocol using a json like format and then generate java code for the specified types and messages. An example of how a schema looks like is below. 

{"namespace": "org.apache.camel.avro.generated",
 "protocol": "KeyValueProtocol",

 "types": [
     {"name": "Key", "type": "record",
      "fields": [
          {"name": "key",   "type": "string"}
      ]
     },
     {"name": "Value", "type": "record",
      "fields": [
          {"name": "value",   "type": "string"}
      ]
     }
 ],

 "messages": {
     "put": {
         "request": [{"name": "key", "type": "Key"}, {"name": "value", "type": "Value"} ],
         "response": "null"
     },
     "get": {
         "request": [{"name": "key", "type": "Key"}],
         "response": "Value"
     }
 }
}

You can easily generate classes from a schema, using maven, ant etc. More details can be found at the Apache Avro documentation.

However, it doesn’t enforce a schema first approach and you can create schema for your existing classes. Since 2.12 you can use existing protocol interfaces to make RCP calls. You should use interface for the protocol itself and POJO beans or primitive/String classes for parameter and result types. Here is an example of the class that corresponds to schema above: 

package org.apache.camel.avro.reflection;

public interface KeyValueProtocol {
    void put(String key, Value value);
    Value get(String key);
}

class Value {
    private String value;
    public String getValue() { return value; }
    public void setValue(String value) { this.value = value; }
}

Note: Existing classes can be used only for RPC (see below), not in data format.

20.2. Using the Avro data format

Using the avro data format is as easy as specifying that the class that you want to marshal or unmarshal in your route. 

    <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
        <route>
            <from uri="direct:in"/>
            <marshal>
                <avro instanceClass="org.apache.camel.dataformat.avro.Message"/>
            </marshal>
            <to uri="log:out"/>
        </route>
    </camelContext>

An alternative can be to specify the dataformat inside the context and reference it from your route. 

    <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
         <dataFormats>
            <avro id="avro" instanceClass="org.apache.camel.dataformat.avro.Message"/>
        </dataFormats>
        <route>
            <from uri="direct:in"/>
            <marshal ref="avro"/>
            <to uri="log:out"/>
        </route>
    </camelContext>

In the same manner you can umarshal using the avro data format.

20.3. Avro Dataformat Options

The Avro dataformat supports 2 options, which are listed below.

NameDefaultJava TypeDescription

instanceClassName

 

String

Class name to use for marshal and unmarshalling

contentTypeHeader

false

Boolean

Whether the data format should set the Content-Type header with the type from the data format if the data format is capable of doing so. For example application/xml for data formats marshalling to XML, or application/json for data formats marshalling to JSon etc.

20.4. Spring Boot Auto-Configuration

The component supports 15 options, which are listed below.

NameDescriptionDefaultType

camel.component.avro.configuration.host

Hostname to use

 

String

camel.component.avro.configuration.message-name

The name of the message to send.

 

String

camel.component.avro.configuration.port

Port number to use

 

Integer

camel.component.avro.configuration.protocol

Avro protocol to use

 

Protocol

camel.component.avro.configuration.protocol-class-name

Avro protocol to use defined by the FQN class name

 

String

camel.component.avro.configuration.protocol-location

Avro protocol location

 

String

camel.component.avro.configuration.reflection-protocol

If protocol object provided is reflection protocol. Should be used only with protocol parameter because for protocolClassName protocol type will be auto detected

false

Boolean

camel.component.avro.configuration.single-parameter

If true, consumer parameter won’t be wrapped into array. Will fail if protocol specifies more then 1 parameter for the message

false

Boolean

camel.component.avro.configuration.transport

Transport to use, can be either http or netty

 

AvroTransport

camel.component.avro.configuration.uri-authority

Authority to use (username and password)

 

String

camel.component.avro.enabled

Enable avro component

true

Boolean

camel.component.avro.resolve-property-placeholders

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

Boolean

camel.dataformat.avro.content-type-header

Whether the data format should set the Content-Type header with the type from the data format if the data format is capable of doing so. For example application/xml for data formats marshalling to XML, or application/json for data formats marshalling to JSon etc.

false

Boolean

camel.dataformat.avro.enabled

Enable avro dataformat

true

Boolean

camel.dataformat.avro.instance-class-name

Class name to use for marshal and unmarshalling

 

String

ND