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A library used at otto.de to implement Spring Boot based event-sourcing microservices.

There is a newer version: 0.33.1

package de.otto.synapse.endpoint;

import de.otto.synapse.message.TextMessage;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

/**
 * Message interceptors are used to intercept messages before they are sent or received by
 * {@link AbstractMessageEndpoint message endpoints}.
 *
 * 
 *     MessageInterceptors will usually be chained using a {@link InterceptorChain}.
 * 
 * 
 *     A {@code MessageInterceptor} can be used in different ways like, for example:
 * 
 * 
 *     Logging
 *     Calculating Metrics
 *     Wire Taps
 *     {@link MessageFilter Message Filters}
 * 
 * 
 *     ...and many other.
 * 
 * 
 *     
 * 
 *
 * @see EIP: Message Filter
 * @see EIP: Wire Taps
 */
@FunctionalInterface
public interface MessageInterceptor {

    /**
     * Intercept a message and return the same message, a modified version of the incoming message, or null, if
     * the message should be filtered out and dropped by the {@link AbstractMessageEndpoint}
     *
     * @param message the channel-layer message with payload-type beeing a String
     * @return intercepted version of the message, or null if the message should be dropped.
     */
    @Nullable
    TextMessage intercept(final @Nonnull TextMessage message);
}