Java 如何使用 GSON 解析 JSON 文件
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how to parse JSON file with GSON
提问by user299791
I have a very simple JSON with reviews for products, like:
我有一个非常简单的 JSON 产品评论，例如：
{
"reviewerID": "A2XVJBSRI3SWDI",
"asin": "0000031887",
"reviewerName": "abigail",
"helpful": [0, 0],
"unixReviewTime": 1383523200,
"reviewText": "Perfect red tutu for the price. ",
"overall": 5.0,
"reviewTime": "11 4, 2013", "summary": "Nice tutu"
}
{
"reviewerID": "A2G0LNLN79Q6HR",
"asin": "0000031887",
"reviewerName": "aj_18 \"Aj_18\"",
"helpful": [1, 1],
"unixReviewTime": 1337990400,
"reviewText": "This was a really cute",
"overall": 4.0,
"reviewTime": "05 26, 2012",
"summary": "Really Cute but rather short."
}
I'd like to read it into my Java app using GSON. I have built a class to hold results for each review:
我想使用 GSON 将其读入我的 Java 应用程序。我建立了一个类来保存每个评论的结果：
public class Review {
private String reviewerID;
private String asin;
private String reviewerName;
private ArrayList<Integer> helpful;
private String reviewText;
private Double overall;
private String summary;
private Long unixReviewTime;
private String reviewTime;
public Review() {
this.helpful = Lists.newArrayList();
}
// some getters and setters...
To read the JSON file, my code is:
要读取 JSON 文件，我的代码是：
Gson gson = new Gson();
JsonReader reader = new JsonReader(new FileReader(filename));
Review data = gson.fromJson(reader, Review.class);
data.toScreen(); // prints to screen some values
With this code, I can only retrieve the first review in the JSON, so my question is: how to iterate through all the reader and get the next reviews? I don't need to store the reviews in a List, just need to access the object once. Any help more than welcome.
使用此代码，我只能检索 JSON 中的第一条评论，所以我的问题是：如何遍历所有读者并获得下一条评论？我不需要将评论存储在列表中，只需要访问一次对象。任何帮助都非常受欢迎。
采纳答案by Archit Maheshwari
You have to fetch the whole data in the list and then do the iteration as it is a file and will become inefficient otherwise.
您必须获取列表中的整个数据，然后进行迭代，因为它是一个文件，否则将变得效率低下。
private static final Type REVIEW_TYPE = new TypeToken<List<Review>>() {
}.getType();
Gson gson = new Gson();
JsonReader reader = new JsonReader(new FileReader(filename));
List<Review> data = gson.fromJson(reader, REVIEW_TYPE); // contains the whole reviews list
data.toScreen(); // prints to screen some values
回答by dieter
just parse as an array:
只需解析为数组：
Review[] reviews = new Gson().fromJson(jsonString, Review[].class);
then if you need you can also create a list in this way:
那么如果您需要，您还可以通过这种方式创建一个列表：
List<Review> asList = Arrays.asList(reviews);
P.S. your json string should be look like this:
PS你的json字符串应该是这样的：
[
{
"reviewerID": "A2SUAM1J3GNN3B1",
"asin": "0000013714",
"reviewerName": "J. McDonald",
"helpful": [2, 3],
"reviewText": "I bought this for my husband who plays the piano.",
"overall": 5.0,
"summary": "Heavenly Highway Hymns",
"unixReviewTime": 1252800000,
"reviewTime": "09 13, 2009"
},
{
"reviewerID": "A2SUAM1J3GNN3B2",
"asin": "0000013714",
"reviewerName": "J. McDonald",
"helpful": [2, 3],
"reviewText": "I bought this for my husband who plays the piano.",
"overall": 5.0,
"summary": "Heavenly Highway Hymns",
"unixReviewTime": 1252800000,
"reviewTime": "09 13, 2009"
},
[...]
]
回答by Constantin Trepadus
In case you need to parse it from a file, I find the best solution to use a HashMap<String, String>to use it inside your java code for better manipultion.
如果您需要从文件中解析它，我找到了使用 aHashMap<String, String>在您的 java 代码中使用它以更好地操作的最佳解决方案。
Try out this code:
试试这个代码：
public HashMap<String, String> myMethodName() throws FileNotFoundException
{
String path = "absolute path to your file";
BufferedReader bufferedReader = new BufferedReader(new FileReader(path));
Gson gson = new Gson();
HashMap<String, String> json = gson.fromJson(bufferedReader, HashMap.class);
return json;
}
