YAML SnakeYAML

Since Camel 2.17

YAML is a Data Format to marshal and unmarshal Java objects to and from YAML.

For YAML to object marshalling, Camel provides integration with three popular YAML libraries:

Every library requires adding the special camel component (see "Dependency…​" paragraphs further down). By default Camel uses the SnakeYAML library.

YAML Options

The YAML SnakeYAML dataformat supports 12 options, which are listed below.

Name Default Java Type Description

library

SnakeYAML

Enum

Which yaml library to use. By default it is SnakeYAML.

Enum values:

  • SnakeYAML

unmarshalType

String

Class name of the java type to use when unmarshalling.

constructor

String

BaseConstructor to construct incoming documents.

representer

String

Representer to emit outgoing objects.

dumperOptions

String

DumperOptions to configure outgoing objects.

resolver

String

Resolver to detect implicit type.

useApplicationContextClassLoader

true

Boolean

Use ApplicationContextClassLoader as custom ClassLoader.

prettyFlow

false

Boolean

Force the emitter to produce a pretty YAML document when using the flow style.

allowAnyType

false

Boolean

Allow any class to be un-marshaled.

typeFilter

Array

Set the types SnakeYAML is allowed to un-marshall.

maxAliasesForCollections

50

Integer

Set the maximum amount of aliases allowed for collections.

allowRecursiveKeys

false

Boolean

Set whether recursive keys are allowed.
SnakeYAML can load any class from YAML definition which may lead to security breach so by default, SnakeYAML DataForma restrict the object it can load to standard Java objects like List or Long. If you want to load custom POJOs you need to add theirs type to SnakeYAML DataFormat type filter list. If your source is trusted, you can set the property allowAnyType to true so SnakeYAML DataForma won’t perform any filter on the types.

Using YAML data format with the SnakeYAML library

  • Turn Object messages into yaml then send to MQSeries

    from("activemq:My.Queue")
  .marshal().yaml()
  .to("mqseries:Another.Queue");
    from("activemq:My.Queue")
  .marshal().yaml(YAMLLibrary.SnakeYAML)
  .to("mqseries:Another.Queue");

  • Restrict classes to be loaded from YAML

    // Creat a SnakeYAMLDataFormat instance
SnakeYAMLDataFormat yaml = new SnakeYAMLDataFormat();

// Restrict classes to be loaded from YAML
yaml.addTypeFilters(TypeFilters.types(MyPojo.class, MyOtherPojo.class));

from("activemq:My.Queue")
  .unmarshal(yaml)
  .to("mqseries:Another.Queue");

Using YAML in Spring DSL

When using Data Format in Spring DSL you need to declare the data formats first. This is done in the DataFormats XML tag.

<dataFormats>
  <!--
    here we define a YAML data format with the id snake and that it should use
    the TestPojo as the class type when doing unmarshal. The unmarshalType
    is optional
  -->
  <yaml
    id="snake"
    library="SnakeYAML"
    unmarshalType="org.apache.camel.component.yaml.model.TestPojo"/>

  <!--
    here we define a YAML data format with the id snake-safe which restricts the
    classes to be loaded from YAML to TestPojo and those belonging to package
    com.mycompany
  -->
  <yaml id="snake-safe">
    <typeFilter value="org.apache.camel.component.yaml.model.TestPojo"/>
    <typeFilter value="com.mycompany\..*" type="regexp"/>
  </yaml>
</dataFormats>

And then you can refer to those ids in the route:

  <route>
    <from uri="direct:unmarshal"/>
    <unmarshal>
      <custom ref="snake"/>
    </unmarshal>
    <to uri="mock:unmarshal"/>
  </route>
  <route>
    <from uri="direct:unmarshal-safe"/>
    <unmarshal>
      <custom ref="snake-safe"/>
    </unmarshal>
    <to uri="mock:unmarshal-safe"/>
  </route>

Dependencies for SnakeYAML

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

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-snakeyaml</artifactId>
  <version>${camel-version}</version>
</dependency>