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20.2. Exchange Interceptors

Exchange Interceptors provide a mechanism for injecting logic into the message path of the SwitchYard exchange bus. You can use an interceptor to read or update message content and context properties, which makes interceptors useful for debugging and for applying logic outside a traditional service implementation in SwitchYard.

20.2.1. Implementing an Exchange Interceptor

The Java class ExchangeInterceptor has the following properties:
  • Implements the org.switchyard.ExchangeInterceptor interface.
  • Is annotated with @Named so that it can be discovered as a CDI bean.
The ExchangeInterceptor interface looks like this: 
public interface ExchangeInterceptor {
    String CONSUMER = "Consumer";
    String PROVIDER = "Provider";
 
    void before(String target, Exchange exchange) throws HandlerException;
    void after(String target, Exchange exchange) throws HandlerException;
    List<String> getTargets();
}
An interceptor is invoked for all message exchanges in an application, so if you only care about a specific service you will want to add a conditional to before() and after() to check for service name. You can restrict the interception points used through the getTargets() method. The CONSUMER and PROVIDER string constants are provided for use with getTargets() to restrict interception to the consumer, provider, or both. The CONSUMER target maps to an injection point just after the consumer sends a request and just before the reply is handed back. The PROVIDER target maps to an injection point just before the provider is called with a request and just after it produces a response.
Here is an example ExchangeInterceptor implementation from the bean-service quickstart: 
package org.switchyard.quickstarts.bean.service;
 
import java.util.Arrays;
import java.util.List;
 
import javax.inject.Named;
 
import org.switchyard.Exchange;
import org.switchyard.ExchangeInterceptor;
import org.switchyard.ExchangeState;
import org.switchyard.HandlerException;
 
/**
 * This is an example of an exchange interceptor which can be used to inject code
 * around targets during a message exchange.  This example updates the content of
 * OrderAck after the provider has generated a response.
 */
@Named("UpdateStatus")
public class OrderInterceptor implements ExchangeInterceptor {
 
    @Override
    public void before(String target, Exchange exchange) throws HandlerException {
        // Not interested in doing anything before the provider is invoked
    }
 
    @Override
    public void after(String target, Exchange exchange) throws HandlerException {
        // We only want to intercept successful replies from OrderService
        if (exchange.getProvider().getName().getLocalPart().equals("OrderService")
                && ExchangeState.OK.equals(exchange.getState())) {
            OrderAck orderAck = exchange.getMessage().getContent(OrderAck.class);
            orderAck.setStatus(orderAck.getStatus() + " [intercepted]");
        }
    }
 
    @Override
    public List<String> getTargets() {
       return Arrays.asList(PROVIDER);
    }
 
}