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Decoder.java
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/**
* Copyright 2012-2020 The Feign 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 feign.codec;
import java.io.IOException;
import java.lang.reflect.Type;
import feign.Feign;
import feign.FeignException;
import feign.Response;
import feign.Util;
/**
* Decodes an HTTP response into a single object of the given {@code type}. Invoked when
* {@link Response#status()} is in the 2xx range and the return type is neither {@code void} nor
* {@code
* Response}.
* <p/>
* <p/>
* Example Implementation:<br>
* <p/>
*
* <pre>
* public class GsonDecoder implements Decoder {
* private final Gson gson = new Gson();
*
* @Override
* public Object decode(Response response, Type type) throws IOException {
* try {
* return gson.fromJson(response.body().asReader(), type);
* } catch (JsonIOException e) {
* if (e.getCause() != null &&
* e.getCause() instanceof IOException) {
* throw IOException.class.cast(e.getCause());
* }
* throw e;
* }
* }
* }
* </pre>
*
* <br/>
* <h3>Implementation Note</h3> The {@code type} parameter will correspond to the
* {@link java.lang.reflect.Method#getGenericReturnType() generic return type} of an
* {@link feign.Target#type() interface} processed by {@link feign.Feign#newInstance(feign.Target)}.
* When writing your implementation of Decoder, ensure you also test parameterized types such as
* {@code
* List<Foo>}. <br/>
* <h3>Note on exception propagation</h3> Exceptions thrown by {@link Decoder}s get wrapped in a
* {@link DecodeException} unless they are a subclass of {@link FeignException} already, and unless
* the client was configured with {@link Feign.Builder#decode404()}.
*/
public interface Decoder {
/**
* Decodes an http response into an object corresponding to its
* {@link java.lang.reflect.Method#getGenericReturnType() generic return type}. If you need to
* wrap exceptions, please do so via {@link DecodeException}.
*
* @param response the response to decode
* @param type {@link java.lang.reflect.Method#getGenericReturnType() generic return type} of the
* method corresponding to this {@code response}.
* @return instance of {@code type}
* @throws IOException will be propagated safely to the caller.
* @throws DecodeException when decoding failed due to a checked exception besides IOException.
* @throws FeignException when decoding succeeds, but conveys the operation failed.
*/
Object decode(Response response, Type type) throws IOException, DecodeException, FeignException;
/** Default implementation of {@code Decoder}. */
public class Default extends StringDecoder {
@Override
public Object decode(Response response, Type type) throws IOException {
if (response.status() == 404 || response.status() == 204)
return Util.emptyValueOf(type);
if (response.body() == null)
return null;
if (byte[].class.equals(type)) {
return Util.toByteArray(response.body().asInputStream());
}
return super.decode(response, type);
}
}
}