com.chalup.gsonadapters.JsonRootAdapterFactory.java Source code

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Here is the source code for com.chalup.gsonadapters.JsonRootAdapterFactory.java

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/*
 * Copyright (C) 2013 Jerzy Chalupski
 *
 * 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 com.chalup.gsonadapters;

import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;

import java.io.IOException;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

public class JsonRootAdapterFactory implements TypeAdapterFactory {

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    public @interface JsonRootName {
        String value();
    }

    @Override
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
        JsonRootName rootAnnotation = typeToken.getRawType().getAnnotation(JsonRootName.class);
        if (rootAnnotation == null) {
            return null;
        }

        TypeAdapter<T> delegateAdapter = gson.getDelegateAdapter(this, typeToken);
        return new Adapter<T>(delegateAdapter, rootAnnotation.value());
    }

    private final static class Adapter<E> extends TypeAdapter<E> {

        private final TypeAdapter<E> mDelegateAdapter;
        private final String mJsonRootName;

        private Adapter(TypeAdapter<E> delegateAdapter, String jsonRootName) {
            mDelegateAdapter = delegateAdapter;
            mJsonRootName = jsonRootName;
        }

        @Override
        public E read(JsonReader in) throws IOException {
            if (in.peek() == JsonToken.NULL) {
                in.nextNull();
                return null;
            }

            in.beginObject();
            in.nextName();
            E instance = mDelegateAdapter.read(in);
            in.endObject();
            return instance;
        }

        @Override
        public void write(JsonWriter out, E value) throws IOException {
            if (value == null) {
                out.nullValue();
                return;
            }

            out.beginObject();
            out.name(mJsonRootName);
            mDelegateAdapter.write(out, value);
            out.endObject();
        }
    }
}