问题

I have a Json string like below

{
"EngineData": [
{
"make": "Toyota",
"transmission": "Manual",
"fuel": "Petrol"
},
{
"make": "GMC",
"transmission": "Auto",
"fuel": "Petrol"
},
{
"make": "Honda",
"transmission": "Manual",
"fuel": "Petrol"
}
]
}

I have the POJO defined like below

@JsonIgnoreProperties(ignoreUnknown = true)
public class EngineData implements Serializable {
@JsonProperty("make")
private String make;
@JsonProperty("transmission")
private String transmission;
@JsonProperty("fuel")
private String fuel;

//getters and setters

}

I wanted to read it to `List<EngineData>`

I wrote the following but it doesn't read the String to a EngineData list

List engineDataList = null;
ObjectMapper mapper = new ObjectMapper();
engineDataList = mapper.readValue(myJsonString, new TypeReference<List>() {
});

Not sure what's wrong in this

<details>
<summary>英文:</summary>

I have a Json string like below

{
"EngineData": [
{
"make": "Toyota",
"transmission": "Manual",
"fuel": "Petrol"
},
{
"make": "GMC",
"transmission": "Auto",
"fuel": "Petrol"
},
{
"make": "Honda",
"transmission": "Manual",
"fuel": "Petrol"
}
]
}

I have the POJO defined like below

@JsonIgnoreProperties(ignoreUnknown = true)
public class EngineData implements Serializable {
@JsonProperty("make")
private String make;
@JsonProperty("transmission")
private String transmission;
@JsonProperty("fuel")
private String fuel;

//getters and setters

}

I wanted to read it to `List<EngineData>`

I wrote the following but it doesn't read the String to a EngineData list

List<EngineData> engineDataList =null;
ObjectMapper mapper = new ObjectMapper();
engineDataList = mapper.readValue(myJsonString, new TypeReference<List<EngineData>>() {
});

Not sure whats wrong in this

</details>


# 答案1
**得分**: 2

你的 JSON 对应于一个对象，如下所示：

```java
class CustomObject {
   List<EngineData> EngineData;
   //...
}

它将与以下 JSON 一起工作：

[
    {
      "make": "Toyota",
      "transmission": "Manual",
      "fuel": "Petrol"
    },
    {
      "make": "GMC",
      "transmission": "Auto",
      "fuel": "Petrol"
    },
    {
      "make": "Honda",
      "transmission": "Manual",
      "fuel": "Petrol"
    }
]

如果你被迫使用这个 JSON，我认为你需要编写一个自定义的反序列化器。详见：https://www.baeldung.com/jackson-deserialization

class CustomObject {
   List<EngineData> EngineData;
   //...
}

[
    {
      "make": "Toyota",
      "transmission": "Manual",
      "fuel": "Petrol"
    },
    {
      "make": "GMC",
      "transmission": "Auto",
      "fuel": "Petrol"
    },
    {
      "make": "Honda",
      "transmission": "Manual",
      "fuel": "Petrol"
    }
  ]

答案2

得分: 0

对象无法映射到列表，

请参考以下内容以映射给定的 JSON：

public class EngineDataList {
   @JsonProperty("EngineData")
   List<EngineData> EngineData;
}

EngineDataList engineDataList = null;
ObjectMapper mapper = new ObjectMapper();
engineDataList = mapper.readValue(myJsonString, new TypeReference<EngineDataList>() {});

public class EngineDataList {
   @JsonProperty("EngineData")
   List<EngineData> EngineData;
}

EngineDataList engineDataList =null;
ObjectMapper mapper = new ObjectMapper();
engineDataList = mapper.readValue(myJsonString, new TypeReference<EngineDataList>() {});