Interceptors and Phases
Interceptors are the fundamental processing unit inside CXF. When a service is invoked, an InterceptorChain is created and invoked. Each interceptor gets a chance to do what they want with the message. This can include reading it, transforming it, processing headers, validating the message, etc.
Interceptors are used with both CXF clients and CXF servers. When a CXF client invokes a CXF server, there is an outgoing interceptor chain for the client and an incoming chain for the server. When the server sends the response back to the client, there is an outgoing chain for the server and an incoming one for the client. Additionally, in the case of SOAPFaults, a CXF web service will create a separate outbound error handling chain and the client will create an inbound error handling chain.
Some examples of interceptors inside CXF include:
- SoapActionInterceptor - Processes the SOAPAction header and selects an operation if it's set.
- StaxInInterceptor - Creates a Stax XMLStreamReader from the transport input stream.
- Attachment(In/Out)Interceptor - Turns a multipart/related message into a series of attachments.
InterceptorChains are divided up into Phases. The phase that each interceptor runs in is declared in the interceptor's constructor. Each phase may contain many interceptors. On the incoming chains, you'll have the following phases:
Transport level processing
Stream level processing/transformations
This is where header reading typically occurs.
Protocol processing, such as JAX-WS SOAP handlers
Unmarshalling of the request
Processing of the umarshalled request
Pre invocation actions
Invocation of the service
Invocation of the outgoing chain if there is one
On the outgoing chain there are the following phases:
Any set up for the following phases
Processing of objects about to marshalled
Opening of the connection
Misc protocol actions.
Writing of the protocol message, such as the SOAP Envelope.
Marshalling of the objects
Processing of the protocol message.
Processing of the byte level message
After the SEND phase, there are a bunch of "*_ENDING" phases that are symmetrical to the above phases to allow the interceptors to cleanup and close anything that they had opened or started in the above phases:
Usually results in all the streams being closed and the final data being sent on the wire.
Several different components inside CXF may provide interceptors to an InterceptorChain. These implement the InterceptorProvider interface:
To add an interceptor to an interceptor chain, you'll want to add it to one of the Interceptor Providers.
Some InterceptorProviders inside CXF are:
Writing and configuring an Interceptor
The CXF distribution is shipped with a demo called configuration_interceptor which shows how to develop a user interceptor and configure the interceptor into its interceptor chain.
Writing an Interceptor
Writing an interceptor is relatively simple. Your interceptor needs to extend from either the AbstractPhaseInterceptor or one of its many subclasses such as AbstractSoapInterceptor. Extending from AbstractPhaseInterceptor allows your interceptor to access the methods of the Message interface. For example, AttachmentInInterceptor is used in CXF to turn a multipart/related message into a series of attachments. It looks like below:
Extending from sub-classes of AbstractPhaseInterceptor allows your interceptor to access more specific information than those in the Message interface. One of the sub-classes of AbstractPhaseInterceptor is AbstractSoapInterceptor. Extending from this class allows your interceptor to access the SOAP header and version information of the SoapMessage class. For example, SoapActionInInterceptor is used in CXF to parse the SOAP action, as a simplified version of it shows below:
Note that you will need to specify the phase that the interceptor will be included in. This is done in the interceptor's constructor:
You can also express that you would like the interceptor to run before/after certain other interceptors defined in the same phase:
You can add your interceptors into the interceptor chain either programmatically or through configuration.
Adding interceptors programmatically
To add this to your server, you'll want to get access to the Server object (see here for more info):
On the Client side the process is very similar:
You can also use annotation to add the interceptors from the SEI or service class. When CXF create the server or client, CXF will add the interceptor according with the annotation.
Adding interceptors through configuration
The configuration file page provides examples on using configuration files to add interceptors.
Adding MyInterceptor to the bus:
For embedded Jetty-based web services, the configuration file can be declared by starting the service with the -Dcxf.config.file=server.xml option. See the server configuration section on the configuration file page for information on specifying the file for servlet WAR file-based web service implementations.
Adding MyInterceptor to your client:
To specify the client-side configuration file, start your client using the -Dcxf.config.file=client.xml option.
CXF contributed interceptors
In CXF, all the functionality of processing messages is done via interceptors. Thus, when debugging a message flow, you will come across a bunch of interceptors in the chain. Here is a list of some of the common interceptors and the functionality they provide. The source code for these interceptors is available on github.
Default JAX-WS Incoming interceptor chain (Server):
- AttachmentInInterceptor Parse the mime headers for mime boundaries, finds the "root" part and resets the input stream to it, and stores the other parts in a collection of Attachments
- StaxInInterceptor Creates an XMLStreamReader from the transport InputStream on the Message
- ReadHeadersInterceptor Parses the SOAP headers and stores them on the Message
- SoapActionInInterceptor Parses "soapaction" header and looks up the operation if a unique operation can be found for that action.
- MustUnderstandInterceptor Checks the MustUnderstand headers, its applicability and process it, if required
- SOAPHandlerInterceptor SOAP Handler as per JAX-WS
- LogicalHandlerInInterceptor Logical Handler as per JAX-WS
- CheckFaultInterceptor Checks for fault, if present aborts interceptor chain and invokes fault handler chain
- URIMappingInterceptor (for CXF versions <= 2.x) Can handle HTTP GET, extracts operation info and sets the same in the Message
- DocLiteralnInterceptor Examines the first element in the SOAP body to determine the appropriate Operation (if soapAction did not find one) and calls the Databinding to read in the data.
- SoapHeaderInterceptor Perform databinding of the SOAP headers for headers that are mapped to parameters
- WrapperClassInInterceptor For wrapped doc/lit, the DocLiteralInInterceptor probably read in a single JAXB bean. This interceptor pulls the individual parts out of that bean to construct the Object needed to invoke the service.
- SwAInInterceptor For Soap w/ Attachments, finds the appropriate attachments and assigns them to the correct spot in the parameter list.
- HolderInInterceptor For OUT and IN/OUT parameters, JAX-WS needs to create Holder objects. This interceptor creates the Holders and puts them in the parameter list.
- ServiceInvokerInInterceptor Actually invokes the service.
Default Outgoing chain stack (Server):
- HolderOutInterceptor For OUT and IN/OUT params, pulls the values out of the JAX-WS Holder objects (created in HolderInInterceptor) and adds them to the param list for the out message.
- SwAOutInterceptor For OUT parts that are Soap attachments, pulls them from the list and holds them for later.
- WrapperClassOutInterceptor For doc/lit wrapped, takes the remaining parts and creates a wrapper JAXB bean to represent the whole message.
- SoapHeaderOutFilterInterceptor Removes inbound marked headers
- SoapActionOutInterceptor Sets the SOAP Action
- MessageSenderInterceptor Calls back to the Destination object to have it setup the output streams, headers, etc... to prepare the outgoing transport.
- SoapPreProtocolOutInterceptor This interceptor is responsible for setting up the SOAP version and header, so that this is available to any pre-protocol interceptors that require these to be available.
- AttachmentOutInterceptor If this service uses attachments (either SwA or if MTOM is enabled), it sets up the Attachment marshallers and the mime stuff that is needed.
- StaxOutInterceptor Creates an XMLStreamWriter from the OutputStream on the Message.
- SoapHandlerInterceptor JAX-WS SOAPHandler
- SoapOutInterceptor Writes start element for soap:envelope and complete elements for other header blocks in the message. Adds start element for soap:body too.
- LogicalHandlerOutInterceptor JAX-WS Logical handler stuff
- WrapperOutInterceptor If wrapped doc/lit and not using a wrapper bean or if RPC lit, outputs the wrapper element to the stream.
- BareOutInterceptor Uses the databinding to write the params out.
- SoapOutInterceptor$SoapOutEndingInterceptor Closes the soap:body and soap:envelope
- StaxOutInterceptor$StaxOutEndingInterceptor Flushes the stax stream.
- MessageSenderInt$MessageSenderEnding Closes the exchange, lets the transport know everything is done and should be flushed to the client.