JsonArrayRequest.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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.android.volley.toolbox;

import com.android.volley.NetworkResponse;
import com.android.volley.ParseError;
import com.android.volley.Response;
import com.android.volley.Response.ErrorListener;
import com.android.volley.Response.Listener;

import org.json.JSONArray;
import org.json.JSONException;

import java.io.UnsupportedEncodingException;

/**
 * A request for retrieving a {@link JSONArray} response body at a given URL.
 */

/*
 * JsonArrayRequest 继承自 JsonRequest<JSONArray>
 * 将 JsonRequest<T> 的泛型 T，设置为 JSONArray
 *
 * 由于 JsonRequest<T> 只是
 * 要求 返回请求结果数据的 格式 ( Response.body ) 指定为 json ( Content-Type：application/json; charset=utf-8 )
 * 再将 请求结果数据 ( Response.body ) 转换为 utf-8 的 byte[]
 *
 *
 */
public class JsonArrayRequest extends JsonRequest<JSONArray> {

    /**
     * Creates a new request.
     * @param url URL to fetch the JSON from
     * @param listener Listener to receive the JSON response
     * @param errorListener Error listener, or null to ignore errors.
     */
    /*
     * Method 默认为：GET 请求
     */
    public JsonArrayRequest(String url, Listener<JSONArray> listener, ErrorListener errorListener) {
        super(Method.GET, url, null, listener, errorListener);
    }

    /**
     * Creates a new request.
     * @param method the HTTP method to use
     * @param url URL to fetch the JSON from
     * @param jsonRequest A {@link JSONArray} to post with the request. Null is allowed and
     *   indicates no parameters will be posted along with request.
     * @param listener Listener to receive the JSON response
     * @param errorListener Error listener, or null to ignore errors.
     */
    public JsonArrayRequest(int method, String url, JSONArray jsonRequest,
                            Listener<JSONArray> listener, ErrorListener errorListener) {
        super(method, url, (jsonRequest == null) ? null : jsonRequest.toString(), listener,
                errorListener);
    }

    /*
     * 解析请求结果 （ NetworkResponse ）
     * 将 body 返回的 json byte[] 转换为 json String
     * 再将 json String 转换为 JSONArray
     *
     * 1. 成功转为 JSONArray 的话，调用 解析数据回调接口
     * 2. 失败的话，Response.error(...) new 一个只有 error 的 Response
     */
    @Override
    protected Response<JSONArray> parseNetworkResponse(NetworkResponse response) {
        try {
            String jsonString = new String(response.data,
                    HttpHeaderParser.parseCharset(response.headers, PROTOCOL_CHARSET));
            return Response.success(new JSONArray(jsonString),
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        } catch (JSONException je) {
            return Response.error(new ParseError(je));
        }
    }
}