Chapter 116. 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. 116.1. Dependencies When using rest with Red Hat build of Camel 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> 116.2. URI format 116.3. Configuring Options Camel components are configured on two separate levels: component level endpoint level 116.3.1. 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. 116.3.2. 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. 116.4. 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 116.5. Endpoint Options The REST endpoint is configured using URI syntax: with the following path and query parameters: 116.5.1. 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. String uriTemplate (common) The uri template. String 116.5.2. 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: InOnly InOut InOptionalOut 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 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 116.6. Supported rest components The following components support rest consumer (Rest DSL): camel-servlet camel-platform-http The following components support rest producer: camel-http 116.7. 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. Note 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 USD{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 USD{header.me}"); from("rest:get:hello:/french/{me}") .transform().simple("Bonjour USD{header.me}"); Note The Rest endpoint path does not accept escaped characters, for example, the plus sign. This is default behavior of Apache Camel 3. 116.8. 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}"); 116.9. 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"); Note You must configure outType option if you want POJO binding to happen for the response messages received from calling the REST service. 116.10. 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. 116.11. Spring Boot Auto-Configuration 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

Commands:
<dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-rest-starter</artifactId> </dependency>
rest://method:path[:uriTemplate]?[options]
rest:method:path:uriTemplate
from("rest:get:hello") .transform().constant("Bye World");
from("rest:get:hello/{me}") .transform().simple("Bye USD{header.me}");
from("rest:get:hello:/{me}") .transform().simple("Hi USD{header.me}"); from("rest:get:hello:/french/{me}") .transform().simple("Bonjour USD{header.me}");
from("direct:start") .to("rest:get:hello/{me}");
template.sendBodyAndHeader("direct:start", null, "me", "Donald Duck");
from("direct:start") .to("rest:get:hello/{me}?host=myserver:8080/foo");
restConfiguration().host("myserver:8080/foo"); from("direct:start") .to("rest:get:hello/{me}");
restConfiguration().host("myserver:8080/foo").producerComponent("http"); from("direct:start") .to("rest:get:hello/{me}");
restConfiguration().component("jetty").host("localhost").port(8080).bindingMode(RestBindingMode.json); from("direct:start") .to("rest:post:user");
UserPojo user = new UserPojo(); user.setId(123); user.setName("Donald Duck"); template.sendBody("direct:start", user);
restConfiguration().component("jetty").host("localhost").port(8080).bindingMode(RestBindingMode.json); from("direct:start") .to("rest:post:user?outType=com.foo.MyResponsePojo");