Quick RESTful web services with the Camel cxfbean component

Trying to create a REST web service using the old Camel cxfrs component was somewhat a pain and not very intuitive in my opinion. It was such a pain I didn't even want to write an example post for it. I really wanted something more automated like Jersey.

Luckly the Apache Camel cxfbean component makes putting together a REST web service much easier. Just annotate your service class and use it as the resource for the cxfbean component.

#!/usr/bin/env groovy

@Grab(group="org.apache.camel", module="camel-core", version="2.8.0")
@Grab(group="org.apache.camel", module="camel-jetty", version="2.8.0")
@Grab(group="org.apache.camel", module="camel-cxf", version="2.8.0")
@Grab(group='ch.qos.logback', module='logback-classic', version='0.9.29')
import org.apache.camel.CamelContext
import org.apache.camel.impl.DefaultCamelContext
import org.apache.camel.impl.SimpleRegistry
import org.apache.camel.builder.RouteBuilder

import javax.ws.rs.*


@Path("/example")
class MyExampleResource{

  @GET
  @Produces("text/plain")
  @Path("hello")
  public String hello(){
    "Hello World!"
  }
}

CamelContext cxt = new DefaultCamelContext()
cxt.registry = new SimpleRegistry()
cxt.registry.registry.put("myResources", [new MyExampleResource()])

cxt.addRoutes(new RouteBuilder(){
  void configure(){
    from("jetty:http://localhost:8080?matchOnUriPrefix=true")
    .to("cxfbean:myResources")
  }
})

cxt.start()

If you want to produce and consume a data format like JSON, you simply pass the necessary processor to the list of cxfbean processors. The CXF libaries include a JSON processor that you can quickly hook up - but I ran into a couple of issues. First you have to annotate your data classes with JAXB annotations (which you may not be able to do depending on your situation.) Second the processor tried to marshal all bean properties (methods that start with get.)

Since I was using Groovy I ran into an issue where Groovy automatically adds a getMetaClass method that returns an Interface and the CXF JSON processor didn't like that. Without an obvious way to tell the processor not to do that I decided to write my own quick processor using the GSON library. Here is a complete example which marshals data in and out from JSON format.

#!/usr/bin/env groovy

@Grab(group="org.apache.camel", module="camel-core", version="2.8.0")
@Grab(group="org.apache.camel", module="camel-jetty", version="2.8.0")
@Grab(group="org.apache.camel", module="camel-cxf", version="2.8.0")
@Grab(group='ch.qos.logback', module='logback-classic', version='0.9.29')
@Grab(group='com.google.code.gson', module='gson', version='1.7.1')
import org.apache.camel.CamelContext
import org.apache.camel.impl.DefaultCamelContext
import org.apache.camel.impl.SimpleRegistry
import org.apache.camel.builder.RouteBuilder

import javax.ws.rs.*

import javax.ws.rs.ext.MessageBodyWriter
import javax.ws.rs.ext.MessageBodyReader
import java.lang.reflect.Type
import java.lang.annotation.Annotation
import javax.ws.rs.core.MediaType
import javax.ws.rs.core.MultivaluedMap
import com.google.gson.Gson


class Person {
  Integer id
  String name

  public String toString(){
      return "$id $name"
  }
}

@Path("/example")
class MyExampleResource{

  @GET
  @Produces("text/plain")
  @Path("hello")
  public String hello(){
    "Hello World!"
  }

  @GET
  @Produces("application/json")
  @Path("person/{id}")
  public Person getPerson(@PathParam("id") Integer id){
    Person p = new Person()
    p.id = id
    p.name = "Bob"
    return p
  }

  @PUT
  @Consumes("application/json")
  @Produces("application/json")
  @Path("person")
  public Person addPerson(Person p){
    println "Received ${p.toString()}"
    p.id = 123
    return p
  }
}

class GsonProvider implements
    MessageBodyWriter<Object>,
    MessageBodyReader<Object>{

    Gson gson = new Gson()

    boolean isWriteable(Class<?> aClass, Type type,
        Annotation[] annotations, MediaType mediaType){
        mediaType.subtype == 'json'
    }

    long getSize(Object t, Class<?> aClass, Type type,
        Annotation[] annotations, MediaType mediaType){
        0
    }

    void writeTo(Object t, Class<?> aClass, Type type,
        Annotation[] annotations, MediaType mediaType,
        MultivaluedMap<String, Object> stringObjectMultivaluedMap,
        OutputStream outputStream)
        throws java.io.IOException, javax.ws.rs.WebApplicationException{
        outputStream.write(gson.toJson(t).bytes)
    }

    Object readFrom(Class<Object> tClass, Type type,
        Annotation[] annotations, MediaType mediaType,
        MultivaluedMap<String, String> stringStringMultivaluedMap,
        InputStream inputStream) {
        gson.fromJson(inputStream.text, tClass)
    }

    boolean isReadable(Class<?> aClass, Type type,
        Annotation[] annotations, MediaType mediaType) {
        mediaType.subtype == 'json'
    }
}


CamelContext cxt = new DefaultCamelContext()
cxt.registry = new SimpleRegistry()
cxt.registry.registry.put("myResources", [new MyExampleResource()])
cxt.registry.registry.put("jsonProvider", new GsonProvider())

cxt.addRoutes(new RouteBuilder(){
  void configure(){
    from("jetty:http://localhost:8080?matchOnUriPrefix=true")
    .to("cxfbean:myResources?providers=#jsonProvider")
  }
})

cxt.start()

Since originally writing this I discovered how to get the JSON parson that comes with CXF to work with Groovy classes. Include the XmlAccessorType annotation telling it to use FIELD.

...
import javax.xml.bind.annotation.XmlRootElement
import javax.xml.bind.annotation.XmlAccessType
import javax.xml.bind.annotation.XmlAccessorType
import org.apache.cxf.jaxrs.provider.JSONProvider
...
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
class Person {
  Integer id
  String name

  public String toString(){
      return "$id $name"
  }
}
...
cxt.registry.registry.put("jsonProvider", new JSONProvider())
...