org.springframework.cloud.stream.function.FunctionInvoker.java Source code

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Here is the source code for org.springframework.cloud.stream.function.FunctionInvoker.java

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/*
 * Copyright 2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.stream.function;

import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Function;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import reactor.core.publisher.Flux;

import org.springframework.cloud.function.context.FunctionCatalog;
import org.springframework.cloud.function.context.FunctionType;
import org.springframework.cloud.function.context.catalog.FunctionInspector;
import org.springframework.cloud.stream.converter.CompositeMessageConverterFactory;
import org.springframework.messaging.Message;
import org.springframework.messaging.converter.CompositeMessageConverter;
import org.springframework.util.Assert;

/**
 *
 * @author Oleg Zhurakousky
 *
 * @param <I> the payload type of the input Message
 * @param <O> the payload type of the output Message
 *
 * @since 2.1
 */
class FunctionInvoker<I, O> implements Function<Flux<Message<I>>, Flux<Message<O>>> {

    private static final Log logger = LogFactory.getLog(FunctionInvoker.class);

    private final Class<?> inputClass;

    private final Function<Flux<?>, Flux<?>> userFunction;

    private final CompositeMessageConverter messageConverter;

    FunctionInvoker(String functionName, FunctionCatalog functionCatalog, FunctionInspector functionInspector,
            CompositeMessageConverterFactory compositeMessageConverterFactory) {
        this.userFunction = functionCatalog.lookup(functionName);
        Assert.isInstanceOf(Function.class, this.userFunction);
        Assert.notNull(this.userFunction, "userFunction: " + functionName + " can not be located.");
        this.messageConverter = compositeMessageConverterFactory.getMessageConverterForAllRegistered();
        FunctionType functionType = functionInspector.getRegistration(this.userFunction).getType();
        this.inputClass = functionType.getInputType();
    }

    @Override
    public Flux<Message<O>> apply(Flux<Message<I>> input) {
        AtomicReference<Message<I>> originalMessage = new AtomicReference<>();
        return input.doOnNext(originalMessage::set) // to preserve the original message
                .map(this::resolveArgument) // resolves argument type before invocation of user function
                .transform(this.userFunction::apply) // invoke user function
                .map(resultMessage -> toMessage(resultMessage, originalMessage.get())); // create output message
    }

    @SuppressWarnings("unchecked")
    private <T> Message<O> toMessage(T value, Message<I> originalMessage) {
        if (logger.isDebugEnabled()) {
            logger.debug("Converting result back to message using the original message: " + originalMessage);
        }
        return (Message<O>) (value instanceof Message ? value
                : this.messageConverter.toMessage(value, originalMessage.getHeaders()));
    }

    @SuppressWarnings("unchecked")
    private <T> T resolveArgument(Message<I> message) {
        if (logger.isDebugEnabled()) {
            logger.debug("Resolving input argument from message: " + message);
        }

        return (T) (shouldConvertFromMessage(message) ? this.messageConverter.fromMessage(message, this.inputClass)
                : message);
    }

    private boolean shouldConvertFromMessage(Message<?> message) {
        return !this.inputClass.isAssignableFrom(byte[].class) && !this.inputClass.isAssignableFrom(Object.class);
    }

}