org.springframework.core.codec.Encoder.java Source code

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Here is the source code for org.springframework.core.codec.Encoder.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.core.codec;

import java.util.List;
import java.util.Map;

import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.ResolvableType;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.lang.Nullable;
import org.springframework.util.MimeType;

/**
 * Strategy to encode a stream of Objects of type {@code <T>} into an output
 * stream of bytes.
 *
 * @author Sebastien Deleuze
 * @author Rossen Stoyanchev
 * @since 5.0
 * @param <T> the type of elements in the input stream
 */
public interface Encoder<T> {

    /**
     * Whether the encoder supports the given source element type and the MIME
     * type for the output stream.
     * @param elementType the type of elements in the source stream
     * @param mimeType the MIME type for the output stream
     * (can be {@code null} if not specified)
     * @return {@code true} if supported, {@code false} otherwise
     */
    boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType);

    /**
     * Encode a stream of Objects of type {@code T} into a {@link DataBuffer}
     * output stream.
     * @param inputStream the input stream of Objects to encode. If the input should be
     * encoded as a single value rather than as a stream of elements, an instance of
     * {@link Mono} should be used.
     * @param bufferFactory for creating output stream {@code DataBuffer}'s
     * @param elementType the expected type of elements in the input stream;
     * this type must have been previously passed to the {@link #canEncode}
     * method and it must have returned {@code true}.
     * @param mimeType the MIME type for the output content (optional)
     * @param hints additional information about how to encode
     * @return the output stream
     */
    Flux<DataBuffer> encode(Publisher<? extends T> inputStream, DataBufferFactory bufferFactory,
            ResolvableType elementType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints);

    /**
     * Encode an Object of type T to a data buffer. This is useful for scenarios
     * that produce a stream of discrete messages (or events) and the
     * content for each is encoded individually.
     * <p>By default this method raises {@link UnsupportedOperationException}
     * and it is expected that some encoders cannot produce a single buffer or
     * cannot do so synchronously (e.g. encoding a {@code Resource}).
     * @param value the value to be encoded
     * @param bufferFactory for creating the output {@code DataBuffer}
     * @param valueType the type for the value being encoded
     * @param mimeType the MIME type for the output content (optional)
     * @param hints additional information about how to encode
     * @return the encoded content
     * @since 5.2
     */
    default DataBuffer encodeValue(T value, DataBufferFactory bufferFactory, ResolvableType valueType,
            @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

        // It may not be possible to produce a single DataBuffer synchronously
        throw new UnsupportedOperationException();
    }

    /**
     * Return the list of mime types this encoder supports.
     */
    List<MimeType> getEncodableMimeTypes();

}