Chapter 252. Protobuf - Protocol Buffers

The Protobuf dataformat supports 3 options which are listed below.

It’s possible to parse JSON message to convert it to the protobuf format and unparse it back using native util converter. To use this option, set contentTypeFormat value to 'json' or call protobuf with second parameter. If default instance is not specified, always use native protobuf format. The sample code shows below:

from("direct:marshal")
    .unmarshal()
    .protobuf("org.apache.camel.dataformat.protobuf.generated.AddressBookProtos$Person", "json")
    .to("mock:reverse");

This quick overview of how to use Protobuf. For more detail see the complete tutorial

The first step is to define the format for the body of your exchange. This is defined in a .proto file as so:

addressbook.proto

syntax = "proto2";

package org.apache.camel.component.protobuf;

option java_package = "org.apache.camel.component.protobuf";
option java_outer_classname = "AddressBookProtos";

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;

  enum PhoneType {
    MOBILE = 0;
    HOME = 1;
    WORK = 2;
  }

  message PhoneNumber {
    required string number = 1;
    optional PhoneType type = 2 [default = HOME];
  }

  repeated PhoneNumber phone = 4;
}

message AddressBook {
  repeated Person person = 1;
}

The Protobuf SDK provides a compiler which will generate the Java classes for the format we defined in our .proto file. If your operating system is supporting by Protobuf Java code generator maven plugin, you can automate protobuf Java code generating by adding following configurations to your pom.xml:

Insert operating system and CPU architecture detection extension inside <build> tag of the project pom.xml or set ${os.detected.classifier} parameter manually

<extensions>
  <extension>
    <groupId>kr.motd.maven</groupId>
    <artifactId>os-maven-plugin</artifactId>
    <version>1.4.1.Final</version>
  </extension>
</extensions>

Insert gRPC and protobuf Java code generator plugin <plugins> tag of the project pom.xml

<plugin>
  <groupId>org.xolstice.maven.plugins</groupId>
  <artifactId>protobuf-maven-plugin</artifactId>
  <version>0.5.0</version>
  <extensions>true</extensions>
  <executions>
    <execution>
      <goals>
        <goal>test-compile</goal>
        <goal>compile</goal>
      </goals>
      <configuration>
        <protocArtifact>com.google.protobuf:protoc:${protobuf-version}:exe:${os.detected.classifier}</protocArtifact>
      </configuration>
    </execution>
  </executions>
</plugin>

You can also run the compiler for any additional supported languages you require manually.

protoc --java_out=. ./proto/addressbook.proto

This will generate a single Java class named AddressBookProtos which contains inner classes for Person and AddressBook. Builders are also implemented for you. The generated classes implement com.google.protobuf.Message which is required by the serialization mechanism. For this reason it important that only these classes are used in the body of your exchanges. Camel will throw an exception on route creation if you attempt to tell the Data Format to use a class that does not implement com.google.protobuf.Message. Use the generated builders to translate the data from any of your existing domain classes.

You can use create the ProtobufDataFormat instance and pass it to Camel DataFormat marshal and unmarshal API like this.

   ProtobufDataFormat format = new ProtobufDataFormat(Person.getDefaultInstance());

   from("direct:in").marshal(format);
   from("direct:back").unmarshal(format).to("mock:reverse");

Or use the DSL protobuf() passing the unmarshal default instance or default instance class name like this.

   // You don't need to specify the default instance for protobuf marshaling
   from("direct:marshal").marshal().protobuf();
   from("direct:unmarshalA").unmarshal()
       .protobuf("org.apache.camel.dataformat.protobuf.generated.AddressBookProtos$Person")
       .to("mock:reverse");

   from("direct:unmarshalB").unmarshal().protobuf(Person.getDefaultInstance()).to("mock:reverse");

The following example shows how to use Protobuf to unmarshal using Spring configuring the protobuf data type

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="direct:start"/>
    <unmarshal>
      <protobuf instanceClass="org.apache.camel.dataformat.protobuf.generated.AddressBookProtos$Person" />
    </unmarshal>
    <to uri="mock:result"/>
  </route>
</camelContext>

To use Protobuf in your camel routes you need to add the a dependency on camel-protobuf which implements this data format.

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