org.eclipse.mdm.nucleus/org.eclipse.mdm.businessobjects/src/main/java/org/eclipse/mdm/businessobjects/utils/JsonMessageBodyProvider.java

/********************************************************************************
 * Copyright (c) 2015-2019 Contributors to the Eclipse Foundation
 *
 * See the NOTICE file(s) distributed with this work for additional
 * information regarding copyright ownership.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 ********************************************************************************/

package org.eclipse.mdm.businessobjects.utils;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.nio.charset.Charset;

import javax.ws.rs.Consumes;
import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;

import com.google.common.base.Charsets;
import com.google.protobuf.GeneratedMessageV3;
import com.google.protobuf.Message;
import com.google.protobuf.util.JsonFormat;
import com.google.protobuf.util.JsonFormat.Parser;
import com.google.protobuf.util.JsonFormat.Printer;

/**
 * MessageBodyProvider for handling json payloads.
 * 
 */
@Provider
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public class JsonMessageBodyProvider implements MessageBodyReader<Message>, MessageBodyWriter<Message> {

	private static final Charset charset = Charsets.UTF_8;
	private Printer jsonPrinter = JsonFormat.printer();
	private Parser jsonParser = JsonFormat.parser();

	/*
	 * (non-Javadoc)
	 * 
	 * @see javax.ws.rs.ext.MessageBodyReader#isReadable(java.lang.Class,
	 * java.lang.reflect.Type, java.lang.annotation.Annotation[],
	 * javax.ws.rs.core.MediaType)
	 */
	@Override
	public boolean isReadable(final Class<?> type, final Type genericType, final Annotation[] annotations,
			final MediaType mediaType) {
		return Message.class.isAssignableFrom(type);
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see javax.ws.rs.ext.MessageBodyReader#readFrom(java.lang.Class,
	 * java.lang.reflect.Type, java.lang.annotation.Annotation[],
	 * javax.ws.rs.core.MediaType, javax.ws.rs.core.MultivaluedMap,
	 * java.io.InputStream)
	 */
	@Override
	public Message readFrom(final Class<Message> type, final Type genericType, final Annotation[] annotations,
			final MediaType mediaType, final MultivaluedMap<String, String> httpHeaders, final InputStream entityStream)
			throws IOException {
		try {
			final Method newBuilder = type.getMethod("newBuilder");
			final GeneratedMessageV3.Builder<?> builder = (GeneratedMessageV3.Builder<?>) newBuilder.invoke(type);
			jsonParser.merge(new InputStreamReader(entityStream, charset), builder);
			return builder.build();
		} catch (Exception e) {
			throw new WebApplicationException(e);
		}
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see javax.ws.rs.ext.MessageBodyWriter#getSize(java.lang.Object,
	 * java.lang.Class, java.lang.reflect.Type, java.lang.annotation.Annotation[],
	 * javax.ws.rs.core.MediaType)
	 */
	@Override
	public long getSize(final Message m, final Class<?> type, final Type genericType, final Annotation[] annotations,
			final MediaType mediaType) {
		return -1;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see javax.ws.rs.ext.MessageBodyWriter#isWriteable(java.lang.Class,
	 * java.lang.reflect.Type, java.lang.annotation.Annotation[],
	 * javax.ws.rs.core.MediaType)
	 */
	@Override
	public boolean isWriteable(final Class<?> type, final Type genericType, final Annotation[] annotations,
			final MediaType mediaType) {
		return Message.class.isAssignableFrom(type);
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see javax.ws.rs.ext.MessageBodyWriter#writeTo(java.lang.Object,
	 * java.lang.Class, java.lang.reflect.Type, java.lang.annotation.Annotation[],
	 * javax.ws.rs.core.MediaType, javax.ws.rs.core.MultivaluedMap,
	 * java.io.OutputStream)
	 */
	@Override
	public void writeTo(final Message m, final Class<?> type, final Type genericType, final Annotation[] annotations,
			final MediaType mediaType, final MultivaluedMap<String, Object> httpHeaders,
			final OutputStream entityStream) throws IOException {
		entityStream.write(jsonPrinter.print(m).getBytes(charset));
	}
}