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

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package de.otto.synapse.consumer;

import de.otto.synapse.message.Message;
import jakarta.annotation.Nonnull;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Objects;
import java.util.regex.Pattern;

/**
 * A {@link MessageConsumer} that is calling a method of a class instance for every accepted {@link Message}
 * 
 *     
 * 

 * @param  The expected type of the message's payload
 */
public class MethodInvokingMessageConsumer implements MessageConsumer {

    private final Pattern keyPattern;
    private final Class payloadType;
    private final Object instance;
    private final Method method;

    public MethodInvokingMessageConsumer(final String keyPattern,
                                         final Class payloadType,
                                         final Object instance,
                                         final Method method) {
        Objects.requireNonNull(keyPattern, "keyPattern must not be null");
        Objects.requireNonNull(payloadType, "payloadType must not be null");
        Objects.requireNonNull(instance, "Unable to build MethodInvokingMessageConsumer: instance parameter is null");
        Objects.requireNonNull(method, "Unable to build MethodInvokingNMessageConsumer: method parameter is null");

        if (method.getParameterCount() != 1) {
            throw new IllegalArgumentException("Unable to build MethodInvokingMessageConsumer: illegal number of arguments");
        }
        final Class paramType = method.getParameterTypes()[0];
        if (!paramType.equals(Message.class)) {
            throw new IllegalArgumentException("Unable to build MethodInvokingMessageConsumer: expected parameter type is Message, not " + paramType.getName());
        }

        this.keyPattern = Pattern.compile(keyPattern);
        this.payloadType = payloadType;
        this.method = method;
        this.instance = instance;
    }

    /**
     * Returns the expected payload type of {@link Message messages} consumed by this MessageConsumer.
     *
     * @return payload type
     */
    @Nonnull
    @Override
    public Class payloadType() {
        return payloadType;
    }

    /**
     * Returns the pattern of {@link Message#getKey()} () message keys} accepted by this consumer.
     *
     * @return Pattern
     */
    @Nonnull
    @Override
    public Pattern keyPattern() {
        return keyPattern;
    }

    @Override
    public void accept(final Message message) {
        try {
            method.invoke(instance, message);
        } catch (IllegalAccessException | InvocationTargetException e) {
            throw new IllegalStateException(e);
        }
    }

}