io.instacount.client.decoders.AbstractInstacountDecoder.java Source code

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Here is the source code for io.instacount.client.decoders.AbstractInstacountDecoder.java

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/**
 * Copyright (C) 2016 Instacount Inc. (developers@instacount.io)
 *
 * 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 io.instacount.client.decoders;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.RuntimeJsonMappingException;
import com.google.common.base.Optional;
import com.google.common.base.Preconditions;

import feign.Response;
import feign.codec.ErrorDecoder;
import io.instacount.client.exceptions.InstacountClientException;
import io.instacount.client.model.Errors;

/**
 * An abstract implementation of {@link ErrorDecoder} for marshaling instacount.io API responses into typed java
 * instances.
 */
public abstract class AbstractInstacountDecoder {
    protected final ObjectMapper objectMapper;

    /**
     * Required-args Constructor.
     *
     * @param objectMapper An instance of {@link ObjectMapper}.
     */
    public AbstractInstacountDecoder(final ObjectMapper objectMapper) {
        this.objectMapper = Preconditions.checkNotNull(objectMapper);
    }

    /**
     * Helper method to construct an instance of {@link Reader} for reading the JSON response from Instacount.
     *
     * @param response
     * @return
     * @throws IOException
     */
    protected Optional<Reader> constructReader(final Response response) throws IOException {
        Preconditions.checkNotNull(response);
        Preconditions.checkNotNull(response.body());

        Reader reader = response.body().asReader();
        if (!reader.markSupported()) {
            reader = new BufferedReader(reader, 1);
        }
        try {
            // Read the first byte to see if we have any data
            reader.mark(1);
            if (reader.read() == -1) {
                // Eagerly returning null avoids "No content to map due to end-of-input"
                return Optional.absent();
            }
            reader.reset();
        } catch (RuntimeJsonMappingException e) {
            if (e.getCause() != null && e.getCause() instanceof IOException) {
                throw IOException.class.cast(e.getCause());
            }
            throw e;
        }

        return Optional.fromNullable(reader);
    }

    /**
     * Construct an instance of {@link Errors} from the supplied {@code response}.
     * 
     * @param response An instance of {@link Response} that contains a response of the Instacount API.
     * @return
     */
    protected Errors constructErrorsResponse(final Response response) throws InstacountClientException {
        try {
            final Errors errorsWithoutHttpCode = objectMapper.readValue(response.body().asInputStream(),
                    Errors.class);
            return new Errors(response.status(), errorsWithoutHttpCode.getErrors());
        } catch (Exception e) {
            throw new InstacountClientException(e, Errors.empty(response.status()));
        }
    }

}