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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>
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20.1. Apache Avro Overview
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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"
     }
 }
}
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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; }
}
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Note: Existing classes can be used only for RPC (see below), not in data format.

20.2. Using the Avro data format
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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>
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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>
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In the same manner you can umarshal using the avro data format.

20.3. Avro Dataformat Options
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The Avro dataformat supports 2 options which are listed below.

Expand
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.

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