JacksonJsonWriter.java

package protobuf.codec.json;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.apache.commons.codec.binary.Base64;
import org.codehaus.jackson.JsonGenerator;

import protobuf.codec.AbstractCodec;
import protobuf.codec.Codec.Feature;

import com.google.protobuf.ByteString;
import com.google.protobuf.Descriptors.EnumValueDescriptor;
import com.google.protobuf.Descriptors.FieldDescriptor;
import com.google.protobuf.Message;
import com.google.protobuf.UnknownFieldSet;

/**
 * Jackson json writer
 * 
 * @author sijuv
 * 
 */
public class JacksonJsonWriter {

    public static void generateJSONFields(Message message, JsonGenerator generator, Map<Feature, Object> featureMap) throws IOException {

        generator.configure(org.codehaus.jackson.JsonGenerator.Feature.AUTO_CLOSE_TARGET, (Boolean) featureMap.get(Feature.CLOSE_STREAM));

        if (AbstractCodec.prettyPrint(featureMap)) {
            generator.useDefaultPrettyPrinter();
        }
        if (!AbstractCodec.closeStream(featureMap)) {
            generator.configure(org.codehaus.jackson.JsonGenerator.Feature.AUTO_CLOSE_TARGET, false);
        }

        generator.writeStartObject();
        Iterator<Map.Entry<FieldDescriptor, Object>> iterator = message.getAllFields().entrySet().iterator(); // Get all set fields
        while (iterator.hasNext()) {
            Map.Entry<FieldDescriptor, Object> record = iterator.next();
            FieldDescriptor field = record.getKey();
            String fieldName = field.isExtension() ? JsonCodec.getExtensionFieldName(field.getName(), featureMap) : field.getName(); // If extn field? box
            fieldName = AbstractCodec.substituteFieldNameForWriting(fieldName, featureMap);
            Object value = record.getValue();
            if (field.isRepeated()) {
                generator.writeArrayFieldStart(fieldName);
                Iterator<?> iter = ((List<?>) value).iterator();
                while (iter.hasNext()) {
                    writeFieldValue(field, iter.next(), generator, featureMap);
                }
                generator.writeEndArray();
            } else {
                generator.writeFieldName(fieldName);
                writeFieldValue(field, value, generator, featureMap);
            }
        }
        if (AbstractCodec.supportUnknownFields(featureMap)) {
            writeUnknownFieldSet(message.getUnknownFields(), generator, featureMap);
        }
        generator.writeEndObject();
    }

    // Extract the field value depending on its java type
    private static void writeFieldValue(FieldDescriptor fieldDesc, Object value, JsonGenerator generator, Map<Feature, Object> featureMap) throws IOException {

        switch (fieldDesc.getJavaType()) {
            case INT:
                generator.writeNumber((Integer) value);
                break;
            case LONG:
                generator.writeNumber((Long) value);
                break;
            case FLOAT:
                generator.writeNumber((Float) value);
                break;
            case DOUBLE:
                generator.writeNumber((Double) value);
                break;
            case BOOLEAN:
                generator.writeBoolean((Boolean) value);
                break;
            case STRING:
                generator.writeString((String) value);
                break;
            case ENUM:
                generator.writeString(((EnumValueDescriptor) value).getName());
                break;
            case BYTE_STRING:
                generator.writeString(Base64.encodeBase64String(((ByteString) value).toByteArray()));
                break;
            case MESSAGE:
                generateJSONFields((Message) value, generator, featureMap);
                break;
            default:
                throw new UnsupportedEncodingException(
                        String.format(
                        "Unspupported protobuf java field type [%s] for field [%s] ",
                        fieldDesc.getJavaType(), fieldDesc.getName()));

        }
    }

    private static void writeUnknownFieldSet(UnknownFieldSet unknownFields, JsonGenerator generator, Map<Feature, Object> featureMap) throws IOException {
        if (unknownFields != null && unknownFields.asMap().size() > 0) {
            generator.writeStringField(AbstractCodec.getUnknownFieldElementName(featureMap),
                    AbstractCodec.encodeUnknownFieldsToString(unknownFields));
        }
    }
}