org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.java Source code

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Here is the source code for org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.java

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/*
 * Copyright 2002-2018 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
 *
 *      https://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.web.method.support;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

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

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.web.context.request.NativeWebRequest;

/**
 * Handles method return values by delegating to a list of registered {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
 * Previously resolved return types are cached for faster lookups.
 *
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public class HandlerMethodReturnValueHandlerComposite implements HandlerMethodReturnValueHandler {

    protected final Log logger = LogFactory.getLog(getClass());

    private final List<HandlerMethodReturnValueHandler> returnValueHandlers = new ArrayList<>();

    /**
     * Return a read-only list with the registered handlers, or an empty list.
     */
    public List<HandlerMethodReturnValueHandler> getHandlers() {
        return Collections.unmodifiableList(this.returnValueHandlers);
    }

    /**
     * Whether the given {@linkplain MethodParameter method return type} is supported by any registered
     * {@link HandlerMethodReturnValueHandler}.
     */
    @Override
    public boolean supportsReturnType(MethodParameter returnType) {
        return getReturnValueHandler(returnType) != null;
    }

    @Nullable
    private HandlerMethodReturnValueHandler getReturnValueHandler(MethodParameter returnType) {
        for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
            if (handler.supportsReturnType(returnType)) {
                return handler;
            }
        }
        return null;
    }

    /**
     * Iterate over registered {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers} and invoke the one that supports it.
     * @throws IllegalStateException if no suitable {@link HandlerMethodReturnValueHandler} is found.
     */
    @Override
    public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
            ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

        HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
        if (handler == null) {
            throw new IllegalArgumentException(
                    "Unknown return value type: " + returnType.getParameterType().getName());
        }
        handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
    }

    @Nullable
    private HandlerMethodReturnValueHandler selectHandler(@Nullable Object value, MethodParameter returnType) {
        boolean isAsyncValue = isAsyncReturnValue(value, returnType);
        for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
            if (isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler)) {
                continue;
            }
            if (handler.supportsReturnType(returnType)) {
                return handler;
            }
        }
        return null;
    }

    private boolean isAsyncReturnValue(@Nullable Object value, MethodParameter returnType) {
        for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
            if (handler instanceof AsyncHandlerMethodReturnValueHandler
                    && ((AsyncHandlerMethodReturnValueHandler) handler).isAsyncReturnValue(value, returnType)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Add the given {@link HandlerMethodReturnValueHandler}.
     */
    public HandlerMethodReturnValueHandlerComposite addHandler(HandlerMethodReturnValueHandler handler) {
        this.returnValueHandlers.add(handler);
        return this;
    }

    /**
     * Add the given {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
     */
    public HandlerMethodReturnValueHandlerComposite addHandlers(
            @Nullable List<? extends HandlerMethodReturnValueHandler> handlers) {

        if (handlers != null) {
            this.returnValueHandlers.addAll(handlers);
        }
        return this;
    }

}