Avro

Since Camel 2.10

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>

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.

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.

Using Avro RPC in Camel

As mentioned above Avro also provides RPC support over multiple transports such as http and netty. Camel provides consumers and producers for these two transports.

avro:[transport]:[host]:[port][?options]

The supported transport values are currently http or netty.

Since 2.12 you can specify message name right in the URI:

avro:[transport]:[host]:[port][/messageName][?options]

For consumers this allows you to have multiple routes attached to the same socket. Dispatching to correct route will be done by the avro component automatically. Route with no messageName specified (if any) will be used as default.

When using camel producers for avro ipc, the "in" message body needs to contain the parameters of the operation specified in the avro protocol. The response will be added in the body of the "out" message.

In a similar manner when using camel avro consumers for avro ipc, the requests parameters will be placed inside the "in" message body of the created exchange and once the exchange is processed the body of the "out" message will be send as a response.

Note: By default consumer parameters are wrapped into array. If you’ve got only one parameter, since 2.12 you can use singleParameter URI option to receive it direcly in the "in" message body without array wrapping.

Avro RPC URI Options

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

Name Description Default Type

configuration (advanced)

To use a shared AvroConfiguration to configure options once

AvroConfiguration

resolveProperty Placeholders (advanced)

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

true

boolean

The Avro endpoint is configured using URI syntax:

avro:transport:host:port/messageName

with the following path and query parameters:

Path Parameters (4 parameters):

Name Description Default Type

transport

Required Transport to use, can be either http or netty

AvroTransport

port

Required Port number to use

int

host

Required Hostname to use

String

messageName

The name of the message to send.

String

Query Parameters (10 parameters):

Name Description Default Type

protocol (common)

Avro protocol to use

Protocol

protocolClassName (common)

Avro protocol to use defined by the FQN class name

String

protocolLocation (common)

Avro protocol location

String

reflectionProtocol (common)

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

singleParameter (common)

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

false

boolean

uriAuthority (common)

Authority to use (username and password)

String

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

exceptionHandler (consumer)

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored.

ExceptionHandler

exchangePattern (consumer)

Sets the exchange pattern when the consumer creates an exchange.

ExchangePattern

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

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

The component supports 15 options, which are listed below.

Name Description Default Type

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

Avro RPC Headers

Name Description

CamelAvroMessageName

The name of the message to send. In consumer overrides message name from URI (if any)

Examples

An example of using camel avro producers via http:

        <route>
            <from uri="direct:start"/>
            <to uri="avro:http:localhost:{{avroport}}?protocolClassName=org.apache.camel.avro.generated.KeyValueProtocol"/>
            <to uri="log:avro"/>
        </route>

In the example above you need to fill CamelAvroMessageName header. Since 2.12 you can use following syntax to call constant messages:

        <route>
            <from uri="direct:start"/>
            <to uri="avro:http:localhost:{{avroport}}/put?protocolClassName=org.apache.camel.avro.generated.KeyValueProtocol"/>
            <to uri="log:avro"/>
        </route>

An example of consuming messages using camel avro consumers via netty:

        <route>
            <from uri="avro:netty:localhost:{{avroport}}?protocolClassName=org.apache.camel.avro.generated.KeyValueProtocol"/>
            <choice>
                <when>
                    <el>${in.headers.CamelAvroMessageName == 'put'}</el>
                    <process ref="putProcessor"/>
                </when>
                <when>
                    <el>${in.headers.CamelAvroMessageName == 'get'}</el>
                    <process ref="getProcessor"/>
                </when>
            </choice>
        </route>

Since 2.12 you can set up two distinct routes to perform the same task:

        <route>
            <from uri="avro:netty:localhost:{{avroport}}/put?protocolClassName=org.apache.camel.avro.generated.KeyValueProtocol">
            <process ref="putProcessor"/>
        </route>
        <route>
            <from uri="avro:netty:localhost:{{avroport}}/get?protocolClassName=org.apache.camel.avro.generated.KeyValueProtocol&singleParameter=true"/>
            <process ref="getProcessor"/>
        </route>

In the example above, get takes only one parameter, so singleParameter is used and getProcessor will receive Value class directly in body, while putProcessor will receive an array of size 2 with String key and Value value filled as array contents.

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