流写作Json [英] Streaming to write Json

问题描述

在 ArrayList 中有一大组 JsonObject 。我需要将这些 JsonObject 添加到 JsonArray 中，并将其写入文件中。

  private void myWriter （List< JsonObject> jsonObjectHolder，int number）throws IOException 
 {
 System.out.println（开始写JSON文件）; 
 //将所有内容添加到JSONArray中
 JsonArray jsonArrayNew = new JsonArray（）; 
 
 for（int i = 0; i< jsonObjectHolder.size（）; i ++）
 {
 //System.out.println(\"inside array：+ i） ; 
 JsonObject o = jsonObjectHolder.get（i）; 
 System.out.println（inside array+ i +：+ o.get（title））; 
 
 jsonArrayNew.add（jsonObjectHolder.get（i））; 
} 
 
 System.out.println（Size：+ jsonArrayNew.size（））; 
 
 //写入文件
文件file = new File（items.json）; 
 
 FileWriter fw = new FileWriter（file）;; 
 fw.write（jsonArrayNew.toString（））; 
 fw.flush（）; 
 fw.close（）; 
 
 System.out.println（outside array）; 
 
 
} 
  

我不喜欢这种方式。 ArrayList 包含大量数据，我写的方式可能会产生 OutOfMemoryError 。相反，我想Stream并将它们写入文件。

更新

<根据SO用户Alden的回答，这里是如何编辑代码的。

  private void myWriter（List< JsonObject> jsonObjectHolder）throws IOException 
 {
 JsonWriter writer = new JsonWriter（new FileWriter（new File（items.json）））; 
 Gson gson = new Gson（）; 
 
 writer.beginArray（）; （jsonObject jsonObject：jsonObjectHolder）
 
 
 {
 gson.toJson（jsonObject，writer）; 
} 
 
 writer.endArray（）; 
 
 writer.close（）; 
} 
  

请让我知道这是否是正确的做法。 p>

解决方案

您可以使用Gson来流式传输您的列表：

<$ p $ （new FileWriter（new File（items.json））;}} $ {code> private void myWriter（List< JsonObject> jsonObjectHolder，Gson gson）throws IOException
{
JsonWriter writer = new JsonWriter ））;

writer.beginArray（）; （jsonObject jsonObject：jsonObjectHolder）


{
gson.toJson（jsonObject，writer）;
}

writer.endArray（）;

writer.close（）;

$ / code>

假设你有一个 Gson 您可以使用的实例。如果你不这样做，你可以使用 writer.beginObject（）和 writer.endObject（）并手动添加属性到作者，但我不会推荐这个，因为你已经完成了构建 JsonObject 的工作。

I have a large set of JsonObjects inside a ArrayList. I need to add these JsonObjects into a JsonArray and write it into a file. I am using Gson and below is my code.

private void myWriter(List<JsonObject> jsonObjectHolder, int number) throws IOException
    {
        System.out.println("Starting to write the JSON File");
        //Add everything into a JSONArray
        JsonArray jsonArrayNew = new JsonArray();

        for(int i=0;i<jsonObjectHolder.size();i++)
        {
            //System.out.println("inside array: "+i);
            JsonObject o = jsonObjectHolder.get(i);
            System.out.println("inside array "+i+": "+o.get("title"));

            jsonArrayNew.add(jsonObjectHolder.get(i));
        }

        System.out.println("Size: "+jsonArrayNew.size());

        //Write it to the File
        File file= new File("items.json");

        FileWriter fw = new FileWriter(file);;
        fw.write(jsonArrayNew.toString());
        fw.flush();
        fw.close();

        System.out.println("outside array");


    }

I don't like this way. The ArrayList holds lot of data and the way I write could generate OutOfMemoryError. Instead, I would like to Stream and write these to the file.

Update

According to the answer of SO user "Alden", here how I edited the code.

private void myWriter(List<JsonObject> jsonObjectHolder) throws IOException
{
    JsonWriter writer = new JsonWriter(new FileWriter(new File("items.json")));
    Gson gson = new Gson();

    writer.beginArray();

    for (JsonObject jsonObject : jsonObjectHolder)
    {
        gson.toJson(jsonObject, writer);
    }

    writer.endArray();

    writer.close();
}

Please let me know whether this is the correct way of doing it.

解决方案

You can use Gson to stream your list like this:

private void myWriter(List<JsonObject> jsonObjectHolder, Gson gson) throws IOException
{
    JsonWriter writer = new JsonWriter(new FileWriter(new File("items.json")));

    writer.beginArray();

    for (JsonObject jsonObject : jsonObjectHolder)
    {
        gson.toJson(jsonObject, writer);
    }

    writer.endArray();

    writer.close();
}

This assumes you have a Gson instance that you can use. If you do not, you can use writer.beginObject() with writer.endObject() and manually add properties to the writer, but I wouldn't recommend this because you've already done the work of building a JsonObject.

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