LfsGson.java

/*
 * Copyright (C) 2017, David Pursehouse <david.pursehouse@gmail.com> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.lfs.server.internal;

import java.io.Reader;

import com.google.gson.FieldNamingPolicy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonIOException;
import com.google.gson.JsonSyntaxException;

/**
 * Wrapper for {@link com.google.gson.Gson} used by LFS servlets.
 */
public class LfsGson {
    private static final Gson gson = new GsonBuilder()
            .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
            .disableHtmlEscaping()
            .create();

    /**
     * Wrapper class only used for serialization of error messages.
     */
    static class Error {
        String message;

        Error(String m) {
            this.message = m;
        }
    }

    /**
     * Serializes the specified object into its equivalent Json representation.
     *
     * @param src
     *            the object for which Json representation is to be created. If
     *            this is a String, it is wrapped in an instance of
     *            {@link org.eclipse.jgit.lfs.server.internal.LfsGson.Error}.
     * @param writer
     *            Writer to which the Json representation needs to be written
     * @throws com.google.gson.JsonIOException
     *             if there was a problem writing to the writer
     * @see Gson#toJson(Object, Appendable)
     */
    public static void toJson(Object src, Appendable writer)
            throws JsonIOException {
        if (src instanceof String) {
            gson.toJson(new Error((String) src), writer);
        } else {
            gson.toJson(src, writer);
        }
    }

    /**
     * Deserializes the Json read from the specified reader into an object of
     * the specified type.
     *
     * @param json
     *            reader producing json from which the object is to be
     *            deserialized
     * @param classOfT
     *            specified type to deserialize
     * @return an Object of type T
     * @throws com.google.gson.JsonIOException
     *             if there was a problem reading from the Reader
     * @throws com.google.gson.JsonSyntaxException
     *             if json is not a valid representation for an object of type
     * @see Gson#fromJson(Reader, java.lang.reflect.Type)
     * @param <T>
     *            a T object.
     */
    public static <T> T fromJson(Reader json, Class<T> classOfT)
            throws JsonSyntaxException, JsonIOException {
        return gson.fromJson(json, classOfT);
    }
}