Name

Restlet — provides Restlet-based endpoints for consuming and producing RESTful resources

Overview

Restlet promotes decoupling of protocol and application concerns. The reference implementation of Restlet Engine supports a number of protocols. However, we have tested the HTTP protocol only.

URI format

The URI format for a Restlet endpoint is:

restlet:restletUrl[?options]

Format of restletUrl:

protocol://hostname[:port][/resourcePattern]

The default port is 80. We do not automatically switch the default port based on the protocol.

You can append query options to the URI in this format: ?option=value&option=value&...

Endpoint options

Table 30, “Restlet endpoint options” lists the options for a Servlet endpoint.

Table 30. Restlet endpoint options

NameDefaultDescription
headerFilterStrategy An instance of RestletHeaderFilterStrategyUse the # notation (headerFilterStrategy=#refName) to reference a header filter strategy in the Camel Registry. The strategy will be plugged into the restlet binding if it is HeaderFilterStrategyAware.
restletBinding An instance of DefaultRestletBindingUse the # notation (restletBinding=#refName) to specify the bean ID of a RestletBinding object in the Camel registry.
restletMethod GET On a producer endpoint, specifies the request method to use. On a consumer endpoint, specifies that the endpoint consumes only restletMethod requests.
restletMethods NoneConsumer only: Specifies one or more methods separated by commas to be serviced by a restlet consumer endpoint. restletMethods takes president over restletMethod.
restletRealm null Use the # notation (restletRealm=#refName) to specify the bean ID of the Realm Map in the Camel registry.
restletUriPatterns NoneConsumer only: Specifies one ore more URI templates to be serviced by a restlet consumer endpoint using the # notation to reference a List<String> in the registry. If a URI pattern has been defined in the endpoint URI, both the URI pattern defined in the endpoint and the restletUriPatterns option will be honored.
throwExceptionOnFailure true Camel 2.6+Producer only: Throws an exception on a producer failure.

Component options

[Important]Important

These component options cannot be configured on the endpoint.

The Restlet component can be configured using the following options (available as Apache Camel 2.10 ) :

NameDefaultDescription
controllerDaemon true Indicates whether the controller thread should be a daemon (not blocking JVM exit).
controllerSleepTimeMs 100 Specifies the time, in milliseconds, for the controller thread to sleep between each control.
inboundBufferSize 8192 Specifies the size of the buffer when reading messages.
minThreads 1 Specifies the minimum number of threads that will wait to service requests.
maxThreads 10 Specifies the maximum number of threads that will service requests.
maxConnectionsPerHost -1 Specifies the maximum number of concurrent connections per host (IP address).
maxTotalConnections -1 Specifies the maximum number of concurrent connections in total.
outboundBufferSize 8192 Specifies the size of the buffer when writing messages.
persistingConnections true Indicates the whether connections should be kept alive after a call.
pipeliningConnections false Indicates the whether pipelining connections are supported.
threadMaxIdleTimeMs 60000 Specifies the time, in milliseconds, for an idle thread to wait for an operation before being collected.
useForwardedForHeader false Looks up the X-Forwarded-For header, supported by popular proxies and caches, and uses it to populate the result of the Request.getClientAddresses method. This information is safe only for intermediary components within the local network. Other addresses could easily be changed by setting a fake header, so should not be trusted for serious security checks.
reuseAddresstrueEnables/disables the SO_REUSEADDR socket option. See the java.io.ServerSocket#reuseAddress property.

Message headers

Restlet endpoints use the following message headers:

NameTypeDescription
Content-Type String Specifies the content type of the response message. If this header is not set, the content type is based on the object type of the OUT message body. If the content type is specified in the IN message, that value determines the content type for the Restlet request message. Otherwise, the content type is defaulted to application/x-www-form-urlencoded.
CamelAcceptContentType String Specifies the HTTP Accept request header.
CamelHttpMethod String Apache Camel 2.9.3: Specifies the HTTP request method. This is set in the IN message header.
CamelHttpQuery String Specifies the query string of the request URI. It is set on the IN message the endpoint receives a request.
CamelHttpResponseCode String or IntegerSpecifies the response code to set on the OUT message by the application/processor. The value is the response code of the response message. If this header is not set, the response code is set by the restlet runtime engine.
CamelHttpUri String Specifies the HTTP request URI. This is set in the IN message header.
CamelRestletLogin String Specifies the login name for basic authentication. It is set on the IN message by the application and gets filtered before the restlet request header.
CamelRestletPassword String Specifies the password for basic authentication. It is set on the IN message by the application and gets filtered before the restlet request header.
CamelRestletRequest Request Apache Camel 2.8: Specifies the org.restlet.Request object that holds all request details.
CamelRestletResponse Response Apache Camel 2.8: Specifies the org.restlet.Response object. You can use this option to create responses using the Restlet API.
org.restlet.*  Specifies the attributes of a Restlet message that get propagated to Apache Camel IN headers.
cache-controlString or List<CacheDirective>Apache Camel 2.11: User can set this option using either a String value or a list of CacheDirective.

Message Body

Apache Camel stores the restlet response from the external server in the OUT body. All headers from the IN message are copied to the OUT message, so that headers are preserved during routing.

Restlet Endpoint with Authentication

The following route starts a restlet consumer endpoint that listens for POST requests on http://localhost:8080 . The processor creates a response that echoes the request body and the value of the id header.

from("restlet:http://localhost:9080/securedOrders?restletMethod=post&restletRealm=#realm").process(new Processor() {
    public void process(Exchange exchange) throws Exception {
        exchange.getOut().setBody(
                "received [" + exchange.getIn().getBody()
                + "] as an order id = "
                + exchange.getIn().getHeader("id"));
    }
});

The restletRealm setting in the URI query is used to look up a Realm Map in the registry. If this option is specified, the restlet consumer uses the information to authenticate user logins. Only authenticated requests can access the resources. In this sample, we create a Spring application context that serves as a registry. The bean ID of the Realm Map should match the restletRealmRef.

<util:map id="realm">
	<entry key="admin" value="foo" />
	<entry key="bar" value="foo" />
</util:map>

The following sample starts a direct endpoint that sends requests to the server on http://localhost:8080 (that is, our restlet consumer endpoint).

// Note: restletMethod and restletRealmRef are stripped 
// from the query before a request is sent as they are 
// only processed by Camel.
from("direct:start-auth").to("restlet:http://localhost:9080/securedOrders?restletMethod=post");

That is all we need. We are ready to send a request and try out the restlet component:

final String id = "89531";

Map<String, Object> headers = new HashMap<String, Object>();
headers.put(RestletConstants.RESTLET_LOGIN, "admin");
headers.put(RestletConstants.RESTLET_PASSWORD, "foo");
headers.put("id", id);

String response = (String) template.requestBodyAndHeaders("direct:start-auth", 
        "<order foo='1'/>", headers);

The sample client sends a request to the direct:start-auth endpoint with the following headers:

  • CamelRestletLogin (used internally by Apache Camel)

  • CamelRestletPassword (used internally by Apache Camel)

  • id (application header)

[Important]Important

org.apache.camel.restlet.auth.login and org.apache.camel.restlet.auth.password will not be propagated as Restlet header.

The sample client gets a response like the following:

received [<order foo='1'/>] as an order id = 89531

Single restlet endpoint to service multiple methods and URI templates (2.0 or later)

It is possible to create a single route to service multiple HTTP methods using the restletMethods option. This snippet also shows how to retrieve the request method from the header:

from("restlet:http://localhost:9080/users/{username}?restletMethods=post,get,put")
    .process(new Processor() {
        public void process(Exchange exchange) throws Exception {
            // echo the method
            exchange.getOut().setBody(exchange.getIn().getHeader(Exchange.HTTP_METHOD,
                                                                 String.class));

        }
    });

In addition to servicing multiple methods, the next snippet shows how to create an endpoint that supports multiple URI templates using the restletUriPatterns option. The request URI is available in the header of the IN message as well. If a URI pattern has been defined in the endpoint URI (which is not the case in this sample), both the URI pattern defined in the endpoint and the restletUriPatterns option will be honored.

from("restlet:http://localhost:9080?restletMethods=post,get&restletUriPatterns=#uriTemplates")
    .process(new Processor() {
        public void process(Exchange exchange) throws Exception {
            // echo the method
            String uri = exchange.getIn().getHeader(Exchange.HTTP_URI, String.class);
            String out = exchange.getIn().getHeader(Exchange.HTTP_METHOD, String.class);
            if ("http://localhost:9080/users/homer".equals(uri)) {
                exchange.getOut().setBody(out + " " + exchange.getIn().getHeader("username", String.class));
            } else if ("http://localhost:9080/atom/collection/foo/component/bar".equals(uri)) {
                exchange.getOut().setBody(out + " " + exchange.getIn().getHeader("id", String.class)
                                          + " " + exchange.getIn().getHeader("cid", String.class));

            }

        }
    });

The restletUriPatterns=#uriTemplates option references the List<String> bean defined in the Spring XML configuration.

<util:list id="uriTemplates">
    <value>/users/{username}</value>
    <value>/atom/collection/{id}/component/{cid}</value>
</util:list>

Using Restlet API to populate response

Available as of Camel 2.8

You may want to use the org.restlet.Response API to populate the response. This gives you full access to the Restlet API and fine grained control of the response. See the route snippet below where we generate the response from an inlined Camel Processor:

from("restlet:http://localhost:" + portNum + "/users/{id}/like/{beer}")
     .process(new Processor() {
         public void process(Exchange exchange) throws Exception {
             // the Restlet request should be available if neeeded
             Request request = exchange.getIn().getHeader(RestletConstants.RESTLET_REQUEST, Request.class);
             assertNotNull("Restlet Request", request);
 
             // use Restlet API to create the response
             Response response = exchange.getIn().getHeader(RestletConstants.RESTLET_RESPONSE, Response.class);
             assertNotNull("Restlet Response", response);
             response.setStatus(Status.SUCCESS_OK);
             response.setEntity("<response>Beer is Good</response>", MediaType.TEXT_XML);
             exchange.getOut().setBody(response);
         }
     });
 

Configuring max threads on component

To configure the max threads options you must do this on the component, such as:

<bean id="restlet" class="org.apache.camel.component.RestletComponent">
  <property name="maxThreads" value="100"/>
</bean>

Using the Restlet servlet within a webapp

Available as of Camel 2.8 There are three ways to configure a Restlet application within a servlet container, and using the subclassed, SpringServerServlet, enables configuration within Camel by injecting the Restlet Component.

Use of the Restlet servlet within a servlet container enables routes to be configured with relative paths in URIs (removing the restrictions of hard-coded absolute URIs) and the hosting servlet container to handle incoming requests (rather than have to spawn a separate server process on a new port).

To configure, add the following to your camel-context.xml;

 <camelContext>
   <route id="RS_RestletDemo">
     <from uri="restlet:/demo/{id}" />
     <transform>
       <simple>Request type : ${header.CamelHttpMethod} and ID : ${header.id}</simple>
     </transform>
   </route> 
 </camelContext>
 
 <bean id="RestletComponent" class="org.restlet.Component" />
 
 <bean id="RestletComponentService" class="org.apache.camel.component.restlet.RestletComponent">
   <constructor-arg index="0">
     <ref bean="RestletComponent" />
   </constructor-arg>
 </bean>

And add this to your web.xml;

 <!-- Restlet Servlet -->
 <servlet>
   <servlet-name>RestletServlet</servlet-name>
   <servlet-class>org.restlet.ext.spring.SpringServerServlet</servlet-class>
   <init-param>
     <param-name>org.restlet.component</param-name>
     <param-value>RestletComponent</param-value>
   </init-param>
 </servlet>
 
 <servlet-mapping>
   <servlet-name>RestletServlet</servlet-name>
   <url-pattern>/rs/*</url-pattern>
 </servlet-mapping>

You will then be able to access the deployed route at http://localhost:8080/mywebapp/rs/demo/1234 where;

localhost:8080 is the server and port of your servlet container mywebapp is the name of your deployed webapp Your browser will then show the following content;

"Request type : GET and ID : 1234"

You will need to add dependency on the Spring extension to restlet which you can do in your Maven pom.xml file:

 <dependency>
   <groupId>org.restlet.jee</groupId>
   <artifactId>org.restlet.ext.spring</artifactId>
   <version>${restlet-version}</version>
 </dependency>

And you would need to add dependency on the restlet maven repository as well:

 <repository>  
    <id>maven-restlet</id>  
    <name>Public online Restlet repository</name>  
    <url>http://maven.restlet.org</url>  
 </repository>

Related topics

The Restlet Project