MVEL

Since Camel 2.0

Camel supports MVEL to do message transformations using MVEL templates.

MVEL is powerful for templates, but can also be used for Expression or Predicate

For example, you can use MVEL in a Predicate with the Content Based Router EIP.

You can use MVEL dot notation to invoke operations. If you for instance have a body that contains a POJO that has a getFamilyName method then you can construct the syntax as follows:

request.body.familyName

Or use similar syntax as in Java:

getRequest().getBody().getFamilyName()

MVEL Options

The MVEL language supports 2 options, which are listed below.

Name Default Java Type Description

resultType

String

Sets the class of the result type (type from output).

trim

true

Boolean

Whether to trim the value to remove leading and trailing whitespaces and line breaks.

Variables

The following Camel related variables are made available:

Variable Type Description

this

Exchange

the Exchange is the root object

context

CamelContext

the CamelContext

exchange

Exchange

the Exchange

exchangeId

String

the exchange id

exception

Throwable

the Exchange exception (if any)

request

Message

the message

message

Message

the message

headers

Map

the message headers

header(name)

Object

the message header by the given name

header(name, type)

Type

the message header by the given name as the given type

properties

Map

the exchange properties

property(name)

Object

the exchange property by the given name

property(name, type)

Type

the exchange property by the given name as the given type

Example

For example, you could use MVEL inside a Message Filter

from("seda:foo")
  .filter().mvel("headers.foo == 'bar'")
    .to("seda:bar");

And in XML:

<route>
  <from uri="seda:foo"/>
  <filter>
    <mvel>headers.foo == 'bar'</mvel>
    <to uri="seda:bar"/>
  </filter>
</route>

Loading script from external resource

You can externalize the script and have Camel load it from a resource such as "classpath:", "file:", or "http:". This is done using the following syntax: "resource:scheme:location", e.g. to refer to a file on the classpath you can do:

.setHeader("myHeader").mvel("resource:classpath:script.mvel")

Dependencies

To use MVEL in your camel routes you need to add the dependency on camel-mvel which implements the MVEL language.

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-mvel</artifactId>
  <version>x.x.x</version>
</dependency>

Spring Boot Auto-Configuration

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

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

The component supports 7 options, which are listed below.

Name Description Default Type

camel.component.mvel.allow-context-map-all

Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API.

false

Boolean

camel.component.mvel.allow-template-from-header

Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care.

false

Boolean

camel.component.mvel.autowired-enabled

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

camel.component.mvel.enabled

Whether to enable auto configuration of the mvel component. This is enabled by default.

Boolean

camel.component.mvel.lazy-start-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

camel.language.mvel.enabled

Whether to enable auto configuration of the mvel language. This is enabled by default.

Boolean

camel.language.mvel.trim

Whether to trim the value to remove leading and trailing whitespaces and line breaks.

true

Boolean
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