001/*
002 * Copyright 2002-2020 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.core.codec;
018
019import java.util.List;
020import java.util.Map;
021
022import org.reactivestreams.Publisher;
023import reactor.core.publisher.Flux;
024import reactor.core.publisher.Mono;
025
026import org.springframework.core.ResolvableType;
027import org.springframework.core.io.buffer.DataBuffer;
028import org.springframework.core.io.buffer.DataBufferFactory;
029import org.springframework.lang.Nullable;
030import org.springframework.util.MimeType;
031
032/**
033 * Strategy to encode a stream of Objects of type {@code <T>} into an output
034 * stream of bytes.
035 *
036 * @author Sebastien Deleuze
037 * @author Rossen Stoyanchev
038 * @since 5.0
039 * @param <T> the type of elements in the input stream
040 */
041public interface Encoder<T> {
042
043        /**
044         * Whether the encoder supports the given source element type and the MIME
045         * type for the output stream.
046         * @param elementType the type of elements in the source stream
047         * @param mimeType the MIME type for the output stream
048         * (can be {@code null} if not specified)
049         * @return {@code true} if supported, {@code false} otherwise
050         */
051        boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType);
052
053        /**
054         * Encode a stream of Objects of type {@code T} into a {@link DataBuffer}
055         * output stream.
056         * @param inputStream the input stream of Objects to encode. If the input should be
057         * encoded as a single value rather than as a stream of elements, an instance of
058         * {@link Mono} should be used.
059         * @param bufferFactory for creating output stream {@code DataBuffer}'s
060         * @param elementType the expected type of elements in the input stream;
061         * this type must have been previously passed to the {@link #canEncode}
062         * method and it must have returned {@code true}.
063         * @param mimeType the MIME type for the output content (optional)
064         * @param hints additional information about how to encode
065         * @return the output stream
066         */
067        Flux<DataBuffer> encode(Publisher<? extends T> inputStream, DataBufferFactory bufferFactory,
068                        ResolvableType elementType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints);
069
070        /**
071         * Encode an Object of type T to a data buffer. This is useful for scenarios,
072         * that distinct messages (or events) are encoded and handled individually,
073         * in fully aggregated form.
074         * <p>By default this method raises {@link UnsupportedOperationException}
075         * and it is expected that some encoders cannot produce a single buffer or
076         * cannot do so synchronously (e.g. encoding a {@code Resource}).
077         * @param value the value to be encoded
078         * @param bufferFactory for creating the output {@code DataBuffer}
079         * @param valueType the type for the value being encoded
080         * @param mimeType the MIME type for the output content (optional)
081         * @param hints additional information about how to encode
082         * @return the encoded content
083         * @since 5.2
084         */
085        default DataBuffer encodeValue(T value, DataBufferFactory bufferFactory,
086                        ResolvableType valueType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
087
088                // It may not be possible to produce a single DataBuffer synchronously
089                throw new UnsupportedOperationException();
090        }
091
092        /**
093         * Return the list of mime types this encoder supports.
094         */
095        List<MimeType> getEncodableMimeTypes();
096
097}