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165 lines (150 loc) · 5.58 KB
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/*
* Copyright © 2012 The Feign Authors (feign@commonhaus.dev)
*
* 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 feign.codec;
import feign.Experimental;
import feign.FeignException;
import feign.Response;
import feign.Util;
import java.io.IOException;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.stream.Collectors;
/**
* A {@link Decoder} that hands each response to the first decoder that accepts it.
*
* <p>Decoders come from two places. A decoder that implements {@link PredicatedDecoder} declares
* its own applicability and can simply be added; any other decoder is paired with a {@link
* DecoderPredicate} at the call site:
*
* <pre>
* Feign.builder()
* .decoder(
* MultiDecoder.builder()
* .add(new JacksonDecoder())
* .add(DecoderPredicate.xmlContentType(), new JAXBDecoder())
* .add((response, type) -> type == byte[].class, new BinaryDecoder())
* .add(DecoderPredicate.any(), new DefaultDecoder())
* .build());
* </pre>
*
* <p>Decoders are consulted in the order they were added, so the narrowest one comes first. There
* is no implicit fallback: a response no decoder accepts fails with a {@link DecodeException}
* naming what was tried. Add a decoder guarded by {@link DecoderPredicate#any()} last to act as a
* default, as above.
*
* @see PredicatedDecoder
* @see DecoderPredicate
*/
@Experimental
public class MultiDecoder implements Decoder {
private final List<PredicatedDecoder> decoders;
private MultiDecoder(List<PredicatedDecoder> decoders) {
this.decoders = Collections.unmodifiableList(new ArrayList<>(decoders));
}
/** Starts building a multi-decoder. */
public static Builder builder() {
return new Builder();
}
/**
* Decodes using the first decoder that accepts the response.
*
* @param response {@inheritDoc}
* @param type {@inheritDoc}
* @return {@inheritDoc}
* @throws IOException {@inheritDoc}
* @throws DecodeException when no decoder accepts the response, or the chosen one fails
* @throws FeignException {@inheritDoc}
*/
@Override
public Object decode(Response response, Type type)
throws IOException, DecodeException, FeignException {
for (PredicatedDecoder decoder : decoders) {
if (decoder.canDecode(response, type)) {
return decoder.decode(response, type);
}
}
throw new DecodeException(
response.status(), unableToDecode(response, type), response.request());
}
private String unableToDecode(Response response, Type type) {
StringBuilder message =
new StringBuilder("Unable to decode ")
.append(response.status())
.append(" response (Content-Type: ")
.append(contentTypes(response))
.append(") as ")
.append(type == null ? "the expected type" : type.getTypeName());
if (decoders.isEmpty()) {
return message.append(". No decoders were configured.").toString();
}
message.append(". Decoders tried, in order:");
for (PredicatedDecoder decoder : decoders) {
message.append("\n - ").append(PairedDecoder.describe(decoder));
}
return message
.append("\nAdd a decoder guarded by DecoderPredicate.any() last to act as a default.")
.toString();
}
private static String contentTypes(Response response) {
String contentTypes =
response.headers().entrySet().stream()
.filter(header -> Util.CONTENT_TYPE.equalsIgnoreCase(header.getKey()))
.map(Map.Entry::getValue)
.filter(Objects::nonNull)
.flatMap(Collection::stream)
.collect(Collectors.joining(", "));
return contentTypes.isEmpty() ? "not set" : contentTypes;
}
@Override
public String toString() {
return "MultiDecoder"
+ decoders.stream().map(PairedDecoder::describe).collect(Collectors.toList());
}
/** Collects the decoders of a {@link MultiDecoder}. */
@Experimental
public static final class Builder {
private final List<PredicatedDecoder> decoders = new ArrayList<>();
private Builder() {}
/**
* Adds a decoder that declares its own applicability.
*
* @param decoder the decoder, consulted via {@link PredicatedDecoder#canDecode}
*/
public Builder add(PredicatedDecoder decoder) {
decoders.add(Objects.requireNonNull(decoder, "decoder cannot be null"));
return this;
}
/**
* Adds any decoder, guarded by the given predicate. Use this for decoders that do not implement
* {@link PredicatedDecoder}, including ones you do not control.
*
* @param predicate decides whether the decoder handles a response
* @param decoder the decoder to delegate to
*/
public Builder add(DecoderPredicate predicate, Decoder decoder) {
return add(PredicatedDecoder.of(predicate, decoder));
}
/** Builds the multi-decoder. */
public MultiDecoder build() {
return new MultiDecoder(decoders);
}
}
}