REST

Since Camel 2.14

Both producer and consumer are supported

The REST component allows defining REST endpoints (consumer) using the Rest DSL and plugin to other Camel components as the REST transport.

The REST component can also be used as a client (producer) to call REST services.

URI format

rest://method:path[:uriTemplate]?[options]

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

At the component level, you set general and shared configurations that are, then, inherited by the endpoints. It is the highest configuration level.

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.

You can configure components using:

  • the Component DSL.

  • in a configuration file (application.properties, *.yaml files, etc).

  • directly in the Java code.

Configuring Endpoint Options

You usually spend more time setting up endpoints because they have many options. These options help you customize what you want the endpoint to do. The options are also categorized into whether the endpoint is used as a consumer (from), as a producer (to), or 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.

Property placeholders provide a few benefits:

  • They help prevent using hardcoded urls, port numbers, sensitive information, and other settings.

  • They allow externalizing the configuration from the code.

  • They help the code to become more flexible and reusable.

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

Component Options

The REST component supports 8 options, which are listed below.

Name Description Default Type

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

consumerComponentName (consumer)

The Camel Rest component to use for the consumer REST transport, such as jetty, servlet, undertow. If no component has been explicitly configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestConsumerFactory is registered in the registry. If either one is found, then that is being used.

String

apiDoc (producer)

The swagger api doc resource to use. The resource is loaded from classpath by default and must be in JSON format.

String

host (producer)

Host and port of HTTP service to use (override host in swagger schema).

String

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

producerComponentName (producer)

The Camel Rest component to use for the producer REST transport, such as http, undertow. If no component has been explicitly configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestProducerFactory is registered in the registry. If either one is found, then that is being used.

String

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

headerFilterStrategy (filter)

To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message.

HeaderFilterStrategy

Endpoint Options

The REST endpoint is configured using URI syntax:

rest:method:path:uriTemplate

With the following path and query parameters:

Path Parameters (3 parameters)

Name Description Default Type

method (common)

Required HTTP method to use.

Enum values:

  • get

  • post

  • put

  • delete

  • patch

  • head

  • trace

  • connect

  • options

String

path (common)

Required The base path, can use * as path suffix to support wildcard HTTP route matching.

String

uriTemplate (common)

The uri template.

String

Query Parameters (16 parameters)

Name Description Default Type

consumes (common)

Media type such as: 'text/xml', or 'application/json' this REST service accepts. By default we accept all kinds of types.

String

inType (common)

To declare the incoming POJO binding type as a FQN class name.

String

outType (common)

To declare the outgoing POJO binding type as a FQN class name.

String

produces (common)

Media type such as: 'text/xml', or 'application/json' this REST service returns.

String

routeId (common)

Name of the route this REST services creates.

String

consumerComponentName (consumer)

The Camel Rest component to use for the consumer REST transport, such as jetty, servlet, undertow. If no component has been explicitly configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestConsumerFactory is registered in the registry. If either one is found, then that is being used.

String

description (consumer)

Human description to document this REST service.

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

apiDoc (producer)

The openapi api doc resource to use. The resource is loaded from classpath by default and must be in JSON format.

String

bindingMode (producer)

Configures the binding mode for the producer. If set to anything other than 'off' the producer will try to convert the body of the incoming message from inType to the json or xml, and the response from json or xml to outType.

Enum values:

  • auto

  • off

  • json

  • xml

  • json_xml

RestBindingMode

host (producer)

Host and port of HTTP service to use (override host in openapi schema).

String

producerComponentName (producer)

The Camel Rest component to use for the producer REST transport, such as http, undertow. If no component has been explicitly configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestProducerFactory is registered in the registry. If either one is found, then that is being used.

String

queryParameters (producer)

Query parameters for the HTTP service to call. The query parameters can contain multiple parameters separated by ampersand such such as foo=123&bar=456.

String

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

Message Headers

The REST component supports 6 message header(s), which is/are listed below:

Name Description Default Type

CamelRestHttpQuery (producer)

Constant: REST_HTTP_QUERY

The query parameters for the rest call to be used.

String

CamelRestHttpUri (producer)

Constant: REST_HTTP_URI

The http uri for the rest call to be used.

String

CamelHttpMethod (producer)

Constant: HTTP_METHOD

The method should be in upper case.

String

Content-Type (producer)

Constant: CONTENT_TYPE

The media type such as: 'text/xml', or 'application/json' this REST service returns.

String

Accept (producer)

Constant: ACCEPT

The media type such as: 'text/xml', or 'application/json' this REST service accepts.

String

CamelHttpResponseCode (producer)

Constant: HTTP_RESPONSE_CODE

The http response code.

Integer

Supported REST components

The following components support the REST consumer (Rest DSL):

  • camel-netty-http

  • camel-jetty

  • camel-servlet

  • camel-undertow

  • camel-platform-http

The following components support the REST producer:

  • camel-http

  • camel-netty-http

  • camel-undertow

  • camel-vertx-http

Path and uriTemplate syntax

The path and uriTemplate option is defined using a REST syntax where you define the REST context path using support for parameters.

If no uriTemplate is configured then path option works the same way.

It does not matter if you configure only path or if you configure both options. Though configuring both a path and uriTemplate is a more common practice with REST.

The following is a Camel route using a path only

from("rest:get:hello")
  .transform().constant("Bye World");

And the following route uses a parameter which is mapped to a Camel header with the key "me".

from("rest:get:hello/{me}")
  .transform().simple("Bye ${header.me}");

The following examples have configured a base path as "hello" and then have two REST services configured using uriTemplates.

from("rest:get:hello:/{me}")
  .transform().simple("Hi ${header.me}");

from("rest:get:hello:/french/{me}")
  .transform().simple("Bonjour ${header.me}");

Rest producer examples

You can use the REST component to call REST services like any other Camel component.

For example, to call a REST service on using hello/{me} you can do

from("direct:start")
  .to("rest:get:hello/{me}");

And then the dynamic value {me} is mapped to a Camel message with the same name. So to call this REST service, you can send an empty message body and a header as shown:

template.sendBodyAndHeader("direct:start", null, "me", "Donald Duck");

The Rest producer needs to know the hostname and port of the REST service, which you can configure using the host option as shown:

from("direct:start")
  .to("rest:get:hello/{me}?host=myserver:8080/foo");

Instead of using the host option, you can configure the host on the restConfiguration as shown:

restConfiguration().host("myserver:8080/foo");

from("direct:start")
  .to("rest:get:hello/{me}");

You can use the producerComponent to select which Camel component to use as the HTTP client, for example to use http, you can do:

restConfiguration().host("myserver:8080/foo").producerComponent("http");

from("direct:start")
  .to("rest:get:hello/{me}");

Rest producer binding

The REST producer supports binding using JSON or XML like the rest-dsl does.

For example, to use jetty with JSON binding mode turned on, you can configure this in the REST configuration:

restConfiguration().component("jetty").host("localhost").port(8080).bindingMode(RestBindingMode.json);

from("direct:start")
  .to("rest:post:user");

Then when calling the REST service using the REST producer, it will automatically bind any POJOs to JSON before calling the REST service:

  UserPojo user = new UserPojo();
  user.setId(123);
  user.setName("Donald Duck");

  template.sendBody("direct:start", user);

In the example above we send a POJO instance UserPojo as the message body. And because we have turned on JSON binding in the REST configuration, then the POJO will be marshalled from POJO to JSON before calling the REST service.

However, if you want to also perform binding for the response message (e.g., what the REST service sends back, as response) you would need to configure the outType option to specify what is the class name of the POJO to unmarshal from JSON to POJO.

For example, if the REST service returns a JSON payload that binds to com.foo.MyResponsePojo you can configure this as shown:

  restConfiguration().component("jetty").host("localhost").port(8080).bindingMode(RestBindingMode.json);

  from("direct:start")
    .to("rest:post:user?outType=com.foo.MyResponsePojo");
You must configure outType option if you want POJO binding to happen for the response messages received from calling the REST service.

More examples

See Rest DSL, which offers more examples and how you can use the Rest DSL to define those in a nicer, restful way.

There is a camel-example-servlet-rest-tomcat example in the Apache Camel distribution, that demonstrates how to use the Rest DSL with Servlet as transport that can be deployed on Apache Tomcat, or similar web containers.

Spring Boot Auto-Configuration

When using rest 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-rest-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 12 options, which are listed below.

Name Description Default Type

camel.component.rest-api.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.rest-api.bridge-error-handler

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

camel.component.rest-api.enabled

Whether to enable auto configuration of the rest-api component. This is enabled by default.

Boolean

camel.component.rest.api-doc

The swagger api doc resource to use. The resource is loaded from classpath by default and must be in JSON format.

String

camel.component.rest.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.rest.bridge-error-handler

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

camel.component.rest.consumer-component-name

The Camel Rest component to use for the consumer REST transport, such as jetty, servlet, undertow. If no component has been explicitly configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestConsumerFactory is registered in the registry. If either one is found, then that is being used.

String

camel.component.rest.enabled

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

Boolean

camel.component.rest.header-filter-strategy

To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message. The option is a org.apache.camel.spi.HeaderFilterStrategy type.

HeaderFilterStrategy

camel.component.rest.host

Host and port of HTTP service to use (override host in swagger schema).

String

camel.component.rest.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.component.rest.producer-component-name

The Camel Rest component to use for the producer REST transport, such as http, undertow. If no component has been explicitly configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestProducerFactory is registered in the registry. If either one is found, then that is being used.

String