Question

到目前为止，我有一个tweet.json文件，里面是tweet的集合。我构建了一个tweet.class，它是来自tweet中键值的对象的集合。

现在我想用jackson实现一个parses，它应该在tweet.json中逐行运行，并且每个tweet（行）都被解析为POJO。所以每一行都是一个POJO

我该怎么做

这就是我所做的

ObjectMapper mapper = new ObjectMapper();
ParsedTweets tweets = mapper.readValue(new File("tweet.json"), tweet.class);

json文件的例子

 {"text": "MVA/Transport. Greater Hume (Hume Hwy, Holbrook, NSW 2644) at 7 Mar 2017 03:58 #NSWRFS #MVATransport", "user": {"id": "4721717942", "name": "NSW Fire Updates"}, "lang": "en", "coordinates": { "coordinates": [147.273696, -35.785469] , "type":"Point"}, "created_at": "Mon Mar 06 17:29:31 +0000 2017"}
{"text": "Yes! Everything happens for a reason. The rain doesn't want the Swedru people to go&amp; flood Westhills mall this evening", "user": {"id": "724288148", "name": "Pyper Pebbles"}, "lang": "en","created_at": "Mon Mar 06 17:19:49 +0000 2017"}
{"text": "5 Sure-Fire Ways That Can Help You Achieve Better Success In Life , "user": {"id": "41049329", "name": "StarCentral Magazine"}, "lang": "en","created_at": "Mon Mar 06 17:08:36 +0000 2017"}

tweet.class

public class Tweet {
private String text;
private String created_at;
private User user;
private Coordinates coordinates;

public Tweet(){

}

public String getText()
{
    return text;
}

public void setText(String text)
{
    this.text = text;
}

public String getCreated_at()
{
    return created_at;
}

public void setCreated_at(String created_at)
{
    this.created_at = created_at;
}

public User getUser()
{
    return user;
}

public void setUser(User user)
{
    this.user = user;
}

public Coordinates getCoordinates()
{
    return coordinates;
}

public void setCoordinates(Coordinates coordinates)
{
    this.coordinates = coordinates;
}

@Override
public String toString()
{
    return "ClassPojo [text = "+text+", created_at = "+created_at+", user = "+user+", coordinates = "+coordinates+"]";
}

}

更新ReadWriteJson实施

public class ReadWriteJson {



 public static void main(String[] args) throws IOException {
        assert args != null & args.length > 0;
        List<Tweet> tweet = new ArrayList<>();
        ObjectMapper mapper = new ObjectMapper();
        try (BufferedReader reader = new BufferedReader(new FileReader("tweets.json"))) {
            String line;
            while ((line = reader.readLine()) != null){
                tweet.add(mapper.readValue(line, Tweet.class));
            }
        }
    }

Answer 1

假设文件包含以下格式的推文：

[{
    "id": "1",
    "text" : "abc"
}, {
    "id": "2",
    "text" : "def"
}]

tweet类包含以下字段：

class tweet {
    private String id;
    private String text;
    //getters and setters
    public String toString(){
        return this.id + "," + this.name + "," + this.text + "," + this.coordinates + "," + this.created_at;
}

您可以使用Jackson的TypeReference反序列化列表，例如：

ObjectMapper mapper = new ObjectMapper();
List<tweet> tweets = mapper.readValue(new File("tweet.json"), new TypeReference<List<tweet>>(){});

<强>更新根据更新的类和文件结构，您需要逐行读取文件（因为它不是有效的json）并将其反序列化为Tweet对象，例如：

public class Test {
    public static void main(String[] args) throws Exception {
        List<Tweet> tweets = new ArrayList<>();
        ObjectMapper mapper = new ObjectMapper();
        try(BufferedReader reader = new BufferedReader(new FileReader("tweet.json"))){
            String line;
            while((line = reader.readLine()) != null){
                tweets.add(mapper.readValue(line, Tweet.class));
            }
        }
    }
}

使用Jackson进行解析器实现

1 个答案: