Fuse ESB - Developing Apache CXF Interceptors - Chapter 6. Manipulating Interceptor Chains on the Fly

Chapter 6. Manipulating Interceptor Chains on the Fly

Interceptors can reconfigure an endpoint's interceptor chain as part of its message processing logic. It can add new interceptors, remove interceptors, reorder interceptors, and even suspend the interceptor chain. Any on-the-fly manipulation is invocation-specific, so the original chain is used each time an endpoint is involved in a message exchange.

Overview

Interceptor chains only live as long as the message exchange that sparked their creation. Each message contains a reference to the interceptor chain responsible for processing it. Developers can use this reference to alter the message's interceptor chain. Because the chain is per-exchange, any changes made to a message's interceptor chain will not effect other message exchanges.

Interceptor chains and the interceptors in the chain are instantiated on a per-invocation basis. When an endpoint is invoked to participate in a message exchange, the required interceptor chains are instantiated along with instances of its interceptors. When the message exchange that caused the creation of the interceptor chain is completed, the chain and its interceptor instances are destroyed.

This means that any changes you make to the interceptor chain or to the fields of an interceptor do not persist across message exchanges. So, if an interceptor places another interceptor in the active chain only the active chain is effected. Any future message exchanges will be created from a pristine state as determined by the endpoint's configuration. It also means that a developer cannot set flags in an interceptor that will alter future message processing.

	Tip
	If an interceptor needs to pass information along to future instances, it can set a property in the message context. The context does persist across message exchanges.

Getting the interceptor chain

The first step in changing a message's interceptor chain is getting the interceptor chain. This is done using the Message.getInterceptorChain() method shown in Example 6.1. The interceptor chain is returned as a org.apache.cxf.interceptor.InterceptorChain object.

Example 6.1. Method for getting an interceptor chain

InterceptorChain getInterceptorChain();

Adding interceptors

The InterceptorChain object has two methods, shown in Example 6.2, for adding interceptors to an interceptor chain. One allows you to add a single interceptor and the other allows you to add multiple interceptors.

Example 6.2. Methods for adding interceptors to an interceptor chain

void add(Interceptor<? extends Message> i);
void add(Collection<Interceptor<? extends Message>> i);

Example 6.3 shows code for adding a single interceptor to a message's interceptor chain.

Example 6.3. Adding an interceptor to an interceptor chain on-the-fly

void handleMessage(Message message)
{
  ...
  AddledIntereptor addled = new AddledIntereptor(); 
  InterceptorChain chain = message.getInterceptorChain(); 
  chain.add(addled); 
  ...
}

The code in Example 6.3 does the following:

Instantiates a copy of the interceptor to be added to the chain.

	Important
	The interceptor being added to the chain should be in either the same phase as the current interceptor or a latter phase than the current interceptor.

Gets the interceptor chain for the current message.

Adds the new interceptor to the chain.

Removing interceptors

The InterceptorChain object has one method, shown in Example 6.4, for removing an interceptor from an interceptor chain.

Example 6.4. Methods for removing interceptors from an interceptor chain

void remove(Interceptor<? extends Message> i);

Example 6.5 shows code for removing an interceptor from a message's interceptor chain.

Example 6.5. Removing an interceptor from an interceptor chain on-the-fly

void handleMessage(Message message)
{
  ...
  SackedIntereptor sacked = new SackedIntereptor(); 
  InterceptorChain chain = message.getInterceptorChain(); 
  chain.remove(sacked); 
  ...
}

The code in Example 6.5 does the following:

Instantiates a copy of the interceptor to be removed from the chain.

	Important
	The interceptor being removed from the chain should be in either the same phase as the current interceptor or a latter phase than the current interceptor.