执行 gson.fromJson(); 时使用 gson + volley 出现内存不足异常；

Question

我正在使用 volley 和 gson 读取一个非常大的 json 文件。我看到我需要使用输入流来克服这个问题，但是如何从网络响应创建输入流？

我已经粘贴了 gson 请求类，它正在从 get 请求中获取响应

public class GsonRequest<T> extends Request<T[]> {

private final Gson gson;
private final Class<T[]> clazz;
private final Map<String, String> headers;
private final Listener<T[]> listener;

public GsonRequest(int method, String url, Class<T[]> clazz,
        Map<String, String> headers, Listener<T[]> listener,
        ErrorListener errorListener) {
    super(method, url, errorListener);

    GsonBuilder gsonBuilder = new GsonBuilder();

    this.gson = gsonBuilder.create();
    this.clazz = clazz;
    this.headers = headers;
    this.listener = listener;
}

@Override
public Map<String, String> getHeaders() throws AuthFailureError {
    return headers != null ? headers : super.getHeaders();
}

@Override
protected void deliverResponse(T[] response) {
    listener.onResponse(response);
}

@Override
protected Response<T[]> parseNetworkResponse(NetworkResponse response) {
    try {

        String json = new String(response.data,
                HttpHeaderParser.parseCharset(response.headers));
        // Log.e("Response", json.toString());
        T[] t = gson.fromJson(json, clazz);

        return Response.success(t,
                HttpHeaderParser.parseCacheHeaders(response));

    } catch (UnsupportedEncodingException e) {
        Log.e("Error", "UnsupportedEncodingException");

        return Response.error(new ParseError(e));
    } catch (JsonSyntaxException e) {
        Log.e("Error", "JsonSyntaxException");

        return Response.error(new ParseError(e));
    }

}

}

我的json数据格式

[
   {
        "salary": "Best In Industry",
        "companyProfile": "string",
        "tags": [
            "mtech"
        ],
    }, {
        "salary": "Best In Industry",
        "companyProfile": "string",
        "tags": [     
            "be/btech",
        ],
     }
]

Answer 1

阅读示例 此代码读取包含消息数组的 JSON 文档。它以流的形式逐步遍历数组元素，以避免将完整的文档加载到内存中。它很简洁，因为它使用 Gson 的对象模型来解析单个消息：

public List<Message> readJsonStream(InputStream in) throws IOException {
    JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
    List<Message> messages = new ArrayList<Message>();
    reader.beginArray();
    while (reader.hasNext()) {
        Message message = gson.fromJson(reader, Message.class);
        messages.add(message);
    }
    reader.endArray();
    reader.close();
    return messages;
}

编写示例

镜像上面的代码，这会编写一个包含消息数组的 JSON 文档。它得益于流式传输的内存效率和对象模型的简洁性：

public void writeJsonStream(OutputStream out, List<Message> messages) throws IOException {
    JsonWriter writer = new JsonWriter(new OutputStreamWriter(out, "UTF-8"));
    writer.setIndent("  ");
    writer.beginArray();
    for (Message message : messages) {
        gson.toJson(message, Message.class, writer);
    }
    writer.endArray();
    writer.close();
}

参考链接https://sites.google.com/site/gson/streaming