Avro RPC

Since Camel 2.10

Both producer and consumer are supported

This component provides support for Apache Avro’s rpc, by providing producers and consumers endpoint for using avro over netty or http. Before Camel 3.2 this functionality was a part of camel-avro component.

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-rpc</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.

Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.

Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.

Configuring Endpoint Options

Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java.

A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.

The following two sections lists all the options, firstly for the component followed by the endpoint.

Component Options

The Avro RPC component supports 10 options, which are listed below.

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 the 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 an array. Will fail if protocol specifies more than one 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 (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

autowiredEnabled (advanced)

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

boolean

configuration (advanced)

To use a shared AvroConfiguration to configure options once.

AvroConfiguration

Endpoint Options

The Avro RPC 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 (common)

Required Transport to use, can be either http or netty.

Enum values:

  • http

  • netty

AvroTransport

port (common)

Required Port number to use.

int

host (common)

Required Hostname to use.

String

messageName (common)

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 the 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 an array. Will fail if protocol specifies more than one parameter for the message.

false

boolean

uriAuthority (common)

Authority to use (username and password).

String

bridgeErrorHandler (consumer (advanced))

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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 (advanced))

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 (advanced))

Sets the exchange pattern when the consumer creates an exchange.

Enum values:

  • InOnly

  • InOut

ExchangePattern

lazyStartProducer (producer (advanced))

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

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. 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 the 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 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.

You can specify the 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 the 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 request parameters will be placed inside the "in" message body of the created exchange. Once the exchange is processed, the body of the "out" message will be sent as a response.

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

Message Headers

The Avro RPC component supports 1 message header(s), which is/are listed below:

Name Description Default Type

CamelAvroMessageName (common)

Constant: AVRO_MESSAGE_NAME

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

String

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.

You can use the 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>

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.

Avro via HTTP SPI

The Avro RPC component offers the org.apache.camel.component.avro.spi.AvroRpcHttpServerFactory service provider interface (SPI) so that various platforms can provide their own implementation based on their native HTTP server.

The default implementation available in org.apache.camel:camel-avro-jetty is based on org.apache.avro:avro-ipc-jetty.