在测试中，在调用网关之前，将ChannelInterceptor添加到submitApplicationChannel。

public interface ChannelInterceptor {
    /**
     * Invoked before the Message is actually sent to the channel.
     * This allows for modification of the Message if necessary.
     * If this method returns {@code null} then the actual
     * send invocation will not occur.
     */
    @Nullable
    default Message<?> preSend(Message<?> message, MessageChannel channel) {
        return message;
    }
    /**
     * Invoked immediately after the send invocation. The boolean
     * value argument represents the return value of that invocation.
     */
    default void postSend(Message<?> message, MessageChannel channel, boolean sent) {
    }
    /**
     * Invoked after the completion of a send regardless of any exception that
     * have been raised thus allowing for proper resource cleanup.
     * <p>Note that this will be invoked only if {@link #preSend} successfully
     * completed and returned a Message, i.e. it did not return {@code null}.
     * @since 4.1
     */
    default void afterSendCompletion(
            Message<?> message, MessageChannel channel, boolean sent, @Nullable Exception ex) {
    }
    /**
     * Invoked as soon as receive is called and before a Message is
     * actually retrieved. If the return value is 'false', then no
     * Message will be retrieved. This only applies to PollableChannels.
     */
    default boolean preReceive(MessageChannel channel) {
        return true;
    }
    /**
     * Invoked immediately after a Message has been retrieved but before
     * it is returned to the caller. The Message may be modified if
     * necessary; {@code null} aborts further interceptor invocations.
     * This only applies to PollableChannels.
     */
    @Nullable
    default Message<?> postReceive(Message<?> message, MessageChannel channel) {
        return message;
    }
    /**
     * Invoked after the completion of a receive regardless of any exception that
     * have been raised thus allowing for proper resource cleanup.
     * <p>Note that this will be invoked only if {@link #preReceive} successfully
     * completed and returned {@code true}.
     * @since 4.1
     */
    default void afterReceiveCompletion(@Nullable Message<?> message, MessageChannel channel,
            @Nullable Exception ex) {
    }
}

字符串