UberJackson2HttpMessageConverter.java

/*
 * Copyright (c) 2015. Escalon System-Entwicklung, Dietrich Schulten
 *
 * 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 de.escalon.hypermedia.spring.uber;

import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import de.escalon.hypermedia.spring.HypermediaTypes;
import org.springframework.hateoas.ResourceSupport;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.AbstractHttpMessageConverter;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.util.Assert;

import java.io.IOException;
import java.nio.charset.Charset;
import java.util.Collection;
import java.util.Map;

public class UberJackson2HttpMessageConverter extends AbstractHttpMessageConverter<Object> {

    private ObjectMapper objectMapper = new ObjectMapper();
    private Boolean prettyPrint;

    public UberJackson2HttpMessageConverter() {
        super(HypermediaTypes.UBER_JSON);
        objectMapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
    }

    @Override
    protected boolean supports(Class<?> clazz) {
        final boolean ret;
        if (ResourceSupport.class.isAssignableFrom(clazz)
                || Collection.class.isAssignableFrom(clazz) || Map.class.isAssignableFrom(clazz)) {
            ret = true;
        } else {
            ret = false;
        }
        return ret;
    }

    @Override
    protected Object readInternal(Class<? extends Object> clazz, HttpInputMessage inputMessage) throws IOException,
            HttpMessageNotReadableException {
        // TODO read uber data
        return null;
    }

    @Override
    protected void writeInternal(Object t, HttpOutputMessage outputMessage) throws IOException,
            HttpMessageNotWritableException {

        UberMessageModel uberModel = new UberMessageModel(t);
        JsonEncoding encoding = getJsonEncoding(outputMessage.getHeaders()
                .getContentType());
        JsonGenerator jsonGenerator = this.objectMapper.getFactory()
                .createGenerator(outputMessage.getBody(), encoding);

        // A workaround for JsonGenerators not applying serialization features
        // https://github.com/FasterXML/jackson-databind/issues/12
        if (this.objectMapper.isEnabled(SerializationFeature.INDENT_OUTPUT)) {
            jsonGenerator.useDefaultPrettyPrinter();
        }

        try {
            this.objectMapper.writeValue(jsonGenerator, uberModel);
        } catch (JsonProcessingException ex) {
            throw new HttpMessageNotWritableException("Could not write JSON: " + ex.getMessage(), ex);
        }
    }

    /**
     * Determine the JSON encoding to use for the given content type.
     *
     * @param contentType
     *         the media type as requested by the caller
     * @return the JSON encoding to use (never {@code null})
     */
    protected JsonEncoding getJsonEncoding(MediaType contentType) {
        if (contentType != null && contentType.getCharSet() != null) {
            Charset charset = contentType.getCharSet();
            for (JsonEncoding encoding : JsonEncoding.values()) {
                if (charset.name()
                        .equals(encoding.getJavaName())) {
                    return encoding;
                }
            }
        }
        return JsonEncoding.UTF8;
    }

    /**
     * Set the {@code ObjectMapper} for this view. If not set, a default {@link com.fasterxml.jackson.databind
     * .ObjectMapper#ObjectMapper()
     * ObjectMapper} is used. Setting a custom-configured {@code ObjectMapper} is one way to take further control of
     * the
     * JSON serialization process. For example, an extended
     * {@link com.fasterxml.jackson.databind.ser.SerializerFactory}
     * can be configured that provides custom serializers for specific types. The other option for refining the
     * serialization process is to use Jackson's provided annotations on the types to be serialized, in which case a
     * custom-configured ObjectMapper is unnecessary.
     *
     * @param objectMapper
     *         used for json mapping
     */
    public void setObjectMapper(ObjectMapper objectMapper) {
        Assert.notNull(objectMapper, "ObjectMapper must not be null");
        this.objectMapper = objectMapper;
        configurePrettyPrint();
    }

    private void configurePrettyPrint() {
        if (this.prettyPrint != null) {
            this.objectMapper.configure(SerializationFeature.INDENT_OUTPUT, this.prettyPrint);
        }
    }
}