How to configure Jsonp and CXF with Interceptors - rest

Question

I am developing a restful WS and I want to give the option to the users to take data back from my WS in the form of XML or Json and also to be able to choose a callback function if they want Jsonp. This is what I have until now and the part with the Interceptors is based on CXF - JAX-RS : Data Bindings.
My Rest Service:
#GET
#Consumes({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
#Produces({ "application/x-javascript", MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
public Response getServers(#Context ServletContext context,
#Context Request request,
#QueryParam("format") String format,
#QueryParam("callback") String callback) {
some code where server object is created....
if(format.equals("json"){
if(callback!= null){
response = Response.status(Status.OK).type("application/x-javascript")
.entity(server).build();
}else{
response = Response.status(Status.OK).type("application/json")
.entity(server).build();
}
} else {
response = Response.status(Status.OK).type("application/xml")
.entity(server).build();
}
return response;
}
My Server object:
#XmlRootElement (name="Server")
public class Server implements Serializable {
private String name=null;
private String hardware = null;
public Server(){
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getHardware() {
return hardware;
}
public void setHardware(String hardware) {
this.hardware = hardware;
}
}
My beans.xml in the WEB-INF:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jaxrs="http://cxf.apache.org/jaxrs"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://cxf.apache.org/jaxrs
http://cxf.apache.org/schemas/jaxrs.xsd">
<import resource="classpath:META-INF/cxf/cxf.xml" />
<context:property-placeholder/>
<context:annotation-config/>
<bean class="org.springframework.web.context.support.ServletContextPropertyPlaceholderConfigurer"/>
<bean class="org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer"/>
<jaxrs:server id="services" address="/">
<jaxrs:serviceBeans>
<bean class="com.ba.serversws_cxf.resources.MyResource" />
</jaxrs:serviceBeans>
<jaxrs:inInterceptors>
<bean class="org.apache.cxf.jaxrs.provider.jsonp.JsonpInInterceptor">
<property name="callbackParam" value="callback"/>
</bean>
</jaxrs:inInterceptors>
<jaxrs:outInterceptors>
<bean class="org.apache.cxf.jaxrs.provider.jsonp.JsonpPreStreamInterceptor">
<property name="mediaType" value="application/x+javascript"/>
</bean>
<bean class="org.apache.cxf.jaxrs.provider.jsonp.JsonpPostStreamInterceptor"/>
</jaxrs:outInterceptors>
<jaxrs:providers>
<bean class="org.codehaus.jackson.jaxrs.JacksonJsonProvider"/>
</jaxrs:providers>
</jaxrs:server>
</beans>
The error that I get when I set the query parameter "callback" is:
org.apache.cxf.jaxrs.interceptor.JAXRSOutInterceptor writeResponseErrorMessage
WARNING: No message body writer has been found for response class Server.
It works fine for other other two cases.
I have searched to find a solution but still nothing.
Any ideas?
Thanks

Answer 1

Here is my class that #Overrides the wrtieTo() method of the org.apache.cxf.jaxrs.provider.json.JSONProvider;
First of all in my beans.xml file I have used the <jaxrs:extensionMappings> and I have declared a jsonp extention.
Here is the code
<jaxrs:server id="services" address="/">
<jaxrs:extensionMappings>
<entry key="xml" value="application/xml" />
<entry key="json" value="application/json" />
<entry key="jsonp" value="application/javascript"/>
</jaxrs:extensionMappings>
</jaxrs:server>
And below is my code of the writeTo() method that I have #Override
import java.io.IOException;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import org.apache.cxf.jaxrs.provider.json.JSONProvider;
import org.apache.cxf.jaxrs.utils.HttpUtils;
#SuppressWarnings("rawtypes")
#Produces("application/javascript")
public class JsonpProvider extends JSONProvider {
#SuppressWarnings("unchecked")
#Override
public void writeTo(Object obj, Class cls, Type genericType,
Annotation[] anns, MediaType m, MultivaluedMap headers,
OutputStream os) throws IOException {
String requestURI = getContext().getHttpServletRequest()
.getRequestURI();
if (requestURI.contains(".jsonp")) {
String prefix = getContext().getHttpServletRequest().getParameter(
"_jsonp");
if (prefix != null && !prefix.isEmpty()) {
os.write(prefix.getBytes(HttpUtils.getSetEncoding(m, headers,
"UTF-8")));
} else {
os.write("callback".getBytes(HttpUtils.getSetEncoding(m,
headers, "UTF-8")));
}
os.write('(');
super.writeTo(obj, cls, genericType, anns, m, headers, os);
os.write(')');
} else {
super.writeTo(obj, cls, genericType, anns, m, headers, os);
}
}
}
So what I am doing in the code above is I am checking if the .jsonp extension has been given to the URL. If yes then I know that I have to return the jsopn with a callback function. The last thing is to set the name of the callback function. If the user has set the _jsonp query parameter to the URL then the value of this parameter will be the name of the callback function. If the _jsonp pquery parameter is null then I put a defult name callback.
And off course in the beans.xml file as a json provider you put the JsonpProvider above:
<jaxrs:providers>
<bean class="org.apache.cxf.jaxrs.ext.search.SearchContextProvider"/>
<bean class="com.ba.serversws_cxf.utils.JsonpProvider">
<property name="ignoreNamespaces" value="true" />
<property name="dropRootElement" value="false" />
<property name="supportUnwrapped" value="true" />
</bean>
</jaxrs:providers>
Hope that helps #bhuvan !