问题

I have translated the provided content. Here's the translated code:

我有一个如下所示的 JSON：

{
"transformationRules": [
{
"targetFieldName": "pageUrlNumber",
"inputPath": "$.metadata.pageUrl",
"rules": [
{
"name": "regex",
"regexPattern": "\d+",
"regexTransformType": "extract",
"order":2
}
]
},
{
"targetFieldName": "categories",
"inputPath": "$.attributes[0].productInfo.breadCrumbs",
"rules": [
{
"name": "transform"
}
]
}
]
}

`rules` 数组具有不同类的 JSON。

我希望根据名称的值即 regex、transform，将上述 JSON 转换为它们的 POJO。我尝试了以下代码。

Rule.java

```java
@NoArgsConstructor
@Data
@JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.EXTERNAL_PROPERTY,
        property = "name")
@JsonSubTypes({
        @JsonSubTypes.Type(value = RegexRule.class, name = "regex"),
        @JsonSubTypes.Type(value = Transform.class, name = "transform"),
})
public abstract class Rule {

    @JsonProperty("name")
    private String name;

    @JsonProperty("order")
    private int order = 1;

    protected Rule(String name, int order) {
        this.name = name;
        this.order = order;
    }

}

RegexRule.java

@NoArgsConstructor
@Data
public class RegexRule extends Rule{

    @JsonProperty("regexPattern")
    private String regexPattern;

    @JsonProperty("regexTransformType")
    private String regexTransformType;

    @JsonProperty("replacementValue")
    private String replacementValue = "";

    @JsonProperty("regexGroupNumber")
    private int regexGroupNumber = 0;

    public RegexRule(String name, int order, String regexPattern, String regexTransformType, String replacementValue, int regexGroupNumber) {
        super(name, order);
        this.regexGroupNumber = regexGroupNumber;
        this.regexPattern = regexPattern;
        this.regexTransformType = regexTransformType;
        this.replacementValue = replacementValue;
    }
}

Transform.java

@NoArgsConstructor
@Data
public class Transform extends Rule{

    public Transform(String name, int order) {
        super(name, order);
    }
}

Main.java

for (TransformationRule transformationRule : getTransformationRules()) {
    for (Rule rule : transformationRule.getRules()) {
        System.out.println(rule.getName());
    }
}

输出：

null
null

在我的 Main 函数中，当我将 JSON 反序列化为 POJO 时，我得到的名称为 null。而我应该得到 regex 和 transform 作为输出。我在这里犯了什么错误？我需要名称用于一个工厂方法。

<details>
<summary>英文:</summary>

I have a json as follows:

{
"transformationRules": [
{
"targetFieldName": "pageUrlNumber",
"inputPath": "$.metadata.pageUrl",
"rules": [
{
"name": "regex",
"regexPattern": "\d+",
"regexTransformType": "extract",
"order":2
}
]
},
{
"targetFieldName": "categories",
"inputPath": "$.attributes[0].productInfo.breadCrumbs",
"rules": [
{
"name": "transform"
}
]
}
]
}

The `rules` array has json of different classes. 

I want convert the above json to their pojos depending on the value of the name i.e regex, transform. I have tried the following code.

Rule.java

@NoArgsConstructor
@Data
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.EXTERNAL_PROPERTY,
property = "name")
@JsonSubTypes({
@JsonSubTypes.Type(value = RegexRule.class, name = "regex"),
@JsonSubTypes.Type(value = Transform.class, name = "transform"),
})
public abstract class Rule {

@JsonProperty("name")
private String name;

@JsonProperty("order")
private int order = 1;

protected Rule(String name, int order) {
    this.name = name;
    this.order = order;
}

}

RegexRule.java

@NoArgsConstructor
@Data
public class RegexRule extends Rule{

@JsonProperty("regexPattern")
private String regexPattern;

@JsonProperty("regexTransformType")
private String regexTransformType;

@JsonProperty("replacementValue")
private String replacementValue = "";

@JsonProperty("regexGroupNumber")
private int regexGroupNumber = 0;

public RegexRule(String name, int order, String regexPattern, String regexTransformType, String replacementValue, int regexGroupNumber) {
    super(name, order);
    this.regexGroupNumber = regexGroupNumber;
    this.regexPattern = regexPattern;
    this.regexTransformType = regexTransformType;
    this.replacementValue = replacementValue;
}

}

Transform.java

@NoArgsConstructor
@Data
public class Transform extends Rule{

public Transform(String name, int order) {
    super(name, order);
}

}

Main.java

for(TransformationRule transformationRule: getTransformationRules()){
for(Rule rule:transformationRule.getRules()){
System.out.println(rule.getName());
}
}

Output:

null
null

In my Main function, when I deserialize the json to the pojos, I'm getting name as null. Instead I should get `regex` and `transform` as output

What mistake have I done here? I need the name for a factory method

</details>


# 答案1
**得分**: 2

`As.EXTERNAL_PROPERTY` 在这里听起来不太对，如果这个方式真的有效，我会感到惊讶，因为这会意味着：

```json
{
  "name": "regex", // 这是*外部*属性，位于上一级
  { // 这是 Rule
    "order": 2,
    ...
  }
}

尝试以下选项：

• As.PROPERTY
  • 你可以从 POJO 中删除 Rule#name，因为它被视为元数据，仅供 Jackson 正确反序列化时使用。记住 rule.getName() == "regex" 和 rule instanceof RegexRule 是一样的。
• As.EXISTING_PROPERTY
  • 将会按预期填充字段，但在大规模使用时可能会稍微影响性能（只有在应用程序持续执行此操作时才会有影响）。
  • 查看 原始功能请求 以获取另一个示例。

{
  "name": "regex", // This is the *external* property, one level up
  { // this is the Rule
    "order": 2,
    ...
  }
}