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  Filters {span}

Filters

Often it's necessary to pre- or post-process some requests according to a number of requirements.
For example, a request like

GET /resource?_type=xml is supported by a CXF specific RequestHandler filter RequestPreprocessor code which modifies the CXF an input Message message
by updating one of its headers.

In some cases users can use the existing filter technologies such as Servler filters or Spring AOP proxies. In other cases, it can be handy
to write a CXF filter which will introspect the resource class, input or output message, the operation which was invoked and modify the request or response accordingly.

Here are the interface definitions :

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import org.apache.cxf.jaxrs.ext.RequestHandler;
import org.apache.cxf.jaxrs.model.ClassResourceInfo;
import org.apache.cxf.message.Message;

public interface RequestHandler {
    
    Response handleRequest(Message inputMessage, 
                           ClassResourceInfo resourceClass);

}

The request handler implementation can either modify the input Message and let the request to proceed or block the request by returning a non-null Response.

A response filter implementation can get an access to OperationResourceInfo object representing a method to be invoked on a resource class :

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OperationResourceInfo ori = exchange.get(OperationResourceInfo.class);

Use OperationResourceInfo in your filter with care. In principle a given request chain may have filters which may want to overwrite Accept or ContentType message headers which might lead to another method be selected. However if you know no such filters (will) exist in your application then you might want to check an OperationResourceInfo instance as part of your filter logic.

When modifying an input message, one would typically want to replace a message input stream or one of its headers, such as ContentType :

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InputStream is = message.getContent(InputStream.class);
message.setContent(new MyFilterInputStream(is));
message.put(Message.ACCEPT_CONTENT_TYPE, "custom/media"); 

A standard mechanism for updating the request or response properties is to use JAX-RS 2.0 ContainerRequestFilter or ContainerResponseFilter.

ContainerRequestFilters with a @PreMatching annotation are run before the JAX-RS resource selection process starts. PreMatching filters should be used to modify request URI or headers or input stream. Post-matching filters are run just before a selected resource method is executed.

Multiple ContainerRequestFilter and ContainerResponseFilter filters can be ordered using a @Priority annotation.

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import javax.ws.rs.core.Response;
import org.apache.cxf.jaxrs.ext.ResponseHandler;
import org.apache.cxf.jaxrs.model.OperationResourceInfo
import org.apache.cxf.message.Message;

public interface ResponseHandler {
    
    Response handleResponse(Message outputMessage,
                           OperationResourceInfo invokedOperation, 
                           Response response);

}

The response handler implementation can optionally overwrite or modify the application Response or modify the output message. When modifying an output message, one may want to either replace an output stream before message body providers attempt to write to it or replace the actual response object :

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// replace an output stream
OutputStream os = message.getContent(OutputStream.class);
message.setContent(new MyFilterOutputStream(os));

// replace an actual object
response.setEntity(new MyWrapper(response.getEntity()))
// or using a low-level Message api if needed
MessageContentsList objs = MessageContentsList.getContentsList(message);
if (objs !== null && objs.size() == 1) {
    Object responseObj = objs.remove(0);
    obj.add(new MyWrapper(responseObj));
}

Please see this blog entry for another example of when response filters can be useful.

Multiple request and response handlers are supported.

The implementations can be registered like any other types type of providers :

<beans>
    <jaxrs:server id="customerService" address="/">
        <jaxrs:serviceBeans>
            <bean class="org.CustomerService" />
        </jaxrs:serviceBeans>

        <jaxrs:providers>
            <ref bean="authorizationFilter" />
        </jaxrs:providers>
        <bean id="authorizationFilter" class="com.bar.providers.AuthorizationRequestHandlerAuthorizationContainerRequestFilter">
            <!-- authorization bean properties -->
        </bean>
    </jaxrs:server>
</beans>

Difference between JAXRS filters and CXF interceptors

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JAXRS filters can be thought of as additional handlers. JAXRSInInterceptor deals with a chain of RequestHandlersPre and Post Match ContainerRequestFilters, just before the invocation. JAXRSOutInterceptor deals with a chain of ResponseHandlersContainerResponseFilters, just after the invocation but before message body writers get their chance.

Sometimes you may want to use CXF interceptors rather than writing JAXRS filters. For example, suppose you combine JAXWS and JAXRS and you need to log only inbound or outbound messages. You can reuse the existing CXF interceptors :

<beans>
    <bean id="logInbound" class="org.apache.cxf.interceptor.LoggingInInterceptor"/>
    <bean id="logOutbound" class="org.apache.cxf.interceptor.LoggingOutInterceptor"/>

    <jaxrs:server> 
        <jaxrs:inInterceptors>
            <ref bean="logInbound"/>
        </jaxrs:inInterceptors>
        <jaxrs:outInterceptors>
            <ref bean="logOutbound"/>
        </jaxrs:outInterceptors>
    </jaxrs:server>

    <jaxws:endpoint>
        <jaxws:inInterceptors>
            <ref bean="logInbound"/>
        </jaxws:inInterceptors>
        <jaxws:outInterceptors>
            <ref bean="logOutbound"/>
        </jaxws:outInterceptors>
    </jaxws:endpoint>

</beans>

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Using filters and interceptors makes it possible to override all the needed request/response properties.

Overriding HTTP method

Register Use @PreMatching ContainerRequestFilter or register a custom RequestHandler CXF in intrerceptor filter which will replace the current method value keyed by
Message.HTTP_REQUEST_METHOD in a given Message.

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One can do it either from a @PreMatching ContainerRequestFilter or CXF input interceptor (registered at the early phase like USER_STREAM) or from a RequestHandler filter, for example :

String s = m.get(Message.REQUEST_URI);
s += "/data/";
m.put(Message.REQUEST_URI, s);

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It is assumed here a user prefers not to use explicit Response objects in the application code.
This can be done either from a ContainerResponseFilter or CXF output interceptor (phase like MARSHALL will do) or from a ResponseHandler filter, for example this code will work for both JAXRS and JAXWS :

import java.util.Map;
import java.util.TreeMap;

import org.apache.cxf.message.Message;
import org.apache.cxf.phase.AbstractPhaseInterceptor;
import org.apache.cxf.phase.Phase;


public class CustomOutInterceptor extends AbstractOutDatabindingInterceptor {
    
    public CustomOutInterceptor() {
        super(Phase.MARSHAL);
    }

    public void handleMessage(Message outMessage) {
        Map<String, List<String>> headers = (Map<String, List<String>>)outMessage.get(Message.PROTOCOL_HEADERS);
        if (headers == null) {
            headers = new TreeMap<String, List<String>>(String.CASE_INSENSITIVE_ORDER);
            message.put(Message.PROTOCOL_HEADERS, headers);
        }
        // modify headers  
    }    

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In some cases you may want to have a JAXRS Response entity which a given RequestHandler or ResponseHandler filter has produced to be directly written to the output stream. For example, a CXF JAXRS WADLGenerator RequestHandler filter produces an XML content which does not have to be serialized by JAXRS MessageBodyWriters. If you do need to have the writers ignored then set the following property on the current exchange in the custom handler :

message.getExchange().put("ignore.message.writers", true);

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Custom invokers can be registered like this :

<beans>

    <jaxrs:server address="/"> 
        <jaxrs:invoker>
            <bean class="org.apache.cxf.systest.jaxrs.CustomJAXRSInvoker"/>
        </jaxrs:invoker>
    </jaxrs:server>

</beans>