Chapter 4. Defining REST Services

The REST DSL (in camel-core) is a facade or wrapper layer that provides a simplified builder API for defining REST services. The REST DSL does not itself provide a REST implementation: it must be combined with an underlying REST implementation. For example, the following Java code shows how to define a simple Hello World service using the REST DSL:

rest("/say")
    .get("/hello/{name}").route().transform().simple("Hello ${header.name}");

For more details, see Section 4.2, “Defining Services with REST DSL”.

The Rest component (in camel-core) is a wrapper layer that enables you to define REST services using a URI syntax. Like the REST DSL, the Rest component does not itself provide a REST implementation: it must be combined with an underlying REST implementation. For example, the following Java code shows how to define a simple Hello World service using the Rest component:

from("rest:get:say:/hello/{name}").transform().simple("Hello ${header.name}");

The Spark-Rest component (in camel-spark-rest) is a REST implementation that enables you to define REST services using a URI syntax. The Spark framework itself is a Java API, which is loosely based on the Sinatra framework (a Python API). For example, the following Java code shows how to define a simple Hello World service using the Spark-Rest component:

from("spark-rest:get:/say/hello/:name").transform().simple("Hello ${header.name}");

Notice that, in contrast to the Rest component, the syntax for a variable in the URI is :name instead of {name}.

The Restlet component (in camel-restlet) is a REST implementation that can, in principle, be layered above different transport protocols (although this component is only tested against the HTTP protocol). This component also provides an integration with the Restlet Framework, which is a commercial framework for developing REST services in Java. For example, the following Java code shows how to define a simple Hello World service using the Restlet component:

from("restlet:http://0.0.0.0:9091/say/hello/{name}?restletMethod=get")
    .transform().simple("Hello ${header.name}");

For more details, see Restlet in the Apache Camel Component Reference Guide.

The Servlet component (in camel-servlet) is a component that binds a Java servlet to a Camel route. In other words, the Servlet component enables you to package and deploy a Camel route as if it was a standard Java servlet. The Servlet component is therefore particularly useful, if you need to deploy a Camel route inside a servlet container (for example, into an Apache Tomcat HTTP server or into a JBoss Enterprise Application Platform container).

The Servlet component on its own, however, does not provide any convenient REST API for defining REST services. The easiest way to use the Servlet component, therefore, is to combine it with the REST DSL, so that you can define REST services with a user-friendly API.

For more details, see Servlet in the Apache Camel Component Reference Guide.

Annotation that can map a context path to a Java class or map a sub-path to a particular Java method.

Annotations that map a HTTP method to a Java method.

Annotation that either maps a URI parameter to a Java method argument, or injects a URI parameter into a field.

Annotation that either maps a query parameter to a Java method argument, or injects a query parameter into a field.