使用Jackson将Java对象转换为JSON

Question

我希望我的JSON看起来像这样:

{
    "information": [{
        "timestamp": "xxxx",
        "feature": "xxxx",
        "ean": 1234,
        "data": "xxxx"
    }, {
        "timestamp": "yyy",
        "feature": "yyy",
        "ean": 12345,
        "data": "yyy"
    }]
}

代码到目前为止:

import java.util.List;

public class ValueData {

    private List<ValueItems> information;

    public ValueData(){

    }

    public List<ValueItems> getInformation() {
        return information;
    }

    public void setInformation(List<ValueItems> information) {
        this.information = information;
    }

    @Override
    public String toString() {
        return String.format("{information:%s}", information);
    }

}

和

public class ValueItems {

    private String timestamp;
    private String feature;
    private int ean;
    private String data;


    public ValueItems(){

    }

    public ValueItems(String timestamp, String feature, int ean, String data){
        this.timestamp = timestamp;
        this.feature = feature;
        this.ean = ean;
        this.data = data;
    }

    public String getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(String timestamp) {
        this.timestamp = timestamp;
    }

    public String getFeature() {
        return feature;
    }

    public void setFeature(String feature) {
        this.feature = feature;
    }

    public int getEan() {
        return ean;
    }

    public void setEan(int ean) {
        this.ean = ean;
    }

    public String getData() {
        return data;
    }

    public void setData(String data) {
        this.data = data;
    }

    @Override
    public String toString() {
        return String.format("{timestamp:%s,feature:%s,ean:%s,data:%s}", timestamp, feature, ean, data);
    }
}

我只是错过了如何用Jackson将Java对象转换为JSON的部分:

public static void main(String[] args) {
   // CONVERT THE JAVA OBJECT TO JSON HERE
    System.out.println(json);
}

我的问题是:我的课程是否正确？我必须调用哪个实例以及如何实现此JSON输出？

Answer 1

object要用杰克逊转换你的JSON:

ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
String json = ow.writeValueAsString(object);

Answer 2

我知道这是旧的(我是java的新手),但我遇到了同样的问题.答案对我来说并不像新手那么清楚...所以我想我会加入我学到的东西.

我使用了第三方库来帮助实现:org.codehaus.jackson 所有下载都可以在这里找到.

对于基本JSON功能,您需要将以下jar添加到项目的库中: jackson-mapper-asl 和 jackson-core-asl

选择项目所需的版本.(通常你可以使用最新的稳定版本).

将它们导入项目库后,将以下行添加import到代码中:

 import org.codehaus.jackson.JsonGenerationException;
 import org.codehaus.jackson.map.JsonMappingException;
 import org.codehaus.jackson.map.ObjectMapper;

使用java对象定义和分配值,您希望将其转换为JSON并作为RESTful Web服务的一部分返回

User u = new User();
u.firstName = "Sample";
u.lastName = "User";
u.email = "sampleU@example.com";

ObjectMapper mapper = new ObjectMapper();

try {
    // convert user object to json string and return it 
    return mapper.writeValueAsString(u);
}
catch (JsonGenerationException | JsonMappingException  e) {
    // catch various errors
    e.printStackTrace();
}

结果应如下所示: {"firstName":"Sample","lastName":"User","email":"sampleU@example.com"}

Answer 3

这可能很有用:

objectMapper.writeValue(new File("c:\\employee.json"), employee);

// display to console
Object json = objectMapper.readValue(
     objectMapper.writeValueAsString(employee), Object.class);

System.out.println(objectMapper.writerWithDefaultPrettyPrinter()
     .writeValueAsString(json));

Answer 4

你可以这样做：

String json = new ObjectMapper().writeValueAsString(yourObjectHere);

Answer 5

就这样做

 for jackson it's
         ObjectMapper mapper = new ObjectMapper();  
         return mapper.writeValueAsString(object);
         //will return json in string


 for gson it's:
            Gson gson = new Gson();
            return Response.ok(gson.toJson(yourClass)).build();

Answer 6

您可以像这样使用 Google Gson

UserEntity user = new UserEntity();
user.setUserName("UserName");
user.setUserAge(18);

Gson gson = new Gson();
String jsonStr = gson.toJson(user);