Chapter 44. REST
Both producer and consumer are supported
The REST component allows to define 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.
44.1. URI format
rest://method:path[:uriTemplate]?[options]
44.2. Configuring Options
Camel components are configured on two separate levels:
- component level
- endpoint level
44.2.1. 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.
44.2.2. 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 as a type safe way of configuring endpoints.
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.
44.3. 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 occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. 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 (consumer) the REST transport, such as jetty, servlet, undertow. If no component has been explicit 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 | |
| componentName (producer) | Deprecated The Camel Rest component to use for (producer) the REST transport, such as http, undertow. If no component has been explicit 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 | |
| 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 (producer) the REST transport, such as http, undertow. If no component has been explicit 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 |
44.4. Endpoint Options
The REST endpoint is configured using URI syntax:
rest:method:path:uriTemplate
with the following path and query parameters:
44.4.1. Path Parameters (3 parameters)
| Name | Description | Default | Type |
|---|---|---|---|
| method (common) | Required HTTP method to use. Enum values:
| String | |
| path (common) | Required The base path. | String | |
| uriTemplate (common) | The uri template. | String |
44.4.2. 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 | |
| bridgeErrorHandler (consumer) | Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. 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 (consumer) the REST transport, such as jetty, servlet, undertow. If no component has been explicit 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 | |
| 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:
| 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:
| RestBindingMode | |
| host (producer) | Host and port of HTTP service to use (override host in openapi 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 (producer) the REST transport, such as http, undertow. If no component has been explicit 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 |
44.5. Supported rest components
The following components support rest consumer (Rest DSL):
- camel-servlet
The following components support rest producer:
- camel-http
44.6. 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}");44.7. 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 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}");44.8. 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 rest producer it will automatic 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 (eg what the REST service send back as response) you would need to configure the outType option to specify what is the classname 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.
44.9. 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.
44.10. 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> </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 occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. 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 occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. 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 (consumer) the REST transport, such as jetty, servlet, undertow. If no component has been explicit 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.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 (producer) the REST transport, such as http, undertow. If no component has been explicit 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 | |
| camel.component.rest.component-name | Deprecated The Camel Rest component to use for (producer) the REST transport, such as http, undertow. If no component has been explicit 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 |
