Question

我们正在尝试编写一个API来创建不同类型的元素。元素具有JPA实体表示。以下代码显示了我们的基本元素结构如何（简化）：

import javax.persistence.*;

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Element {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column
    private String type;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }
}

每个元素实现看起来都不一样，但这个例子应该足够了：

import javax.persistence.Column;
import javax.persistence.Entity;

@Entity
public class SpecializedElement1 extends Element {

    @Column
    private String attribute;

    public String getAttribute() {
        return attribute;
    }

    public void setAttribute(String attribute) {
        this.attribute = attribute;
    }

}

我们使用Jackson，典型的控制器动作如下：

@RequestMapping(value = "/createElement", method = RequestMethod.POST)
@ResponseBody
public HashMap<String, Object> create(@RequestBody Element element) {
    HashMap<String, Object> response = new HashMap<String, Object>()
    response.put("element", element);
    response.put("status", "success");
    return response;
}

典型的请求正文如下所示：

{
    "type": "constantStringForSpecializedElement1"
    "text": "Bacon ipsum dolor sit amet cow bacon drumstick shankle ham hock hamburger."
}

正如您将看到的：由于Jackson不知道如何将此对象映射到SpecializedElement1，因此无效。

问题是：我怎样才能做到这一点？

Answer 1

我明白了。这是解决方案：

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@JsonTypeInfo(
    // We use the name defined in @JsonSubTypes.Type to map a type to its implementation.
    use = JsonTypeInfo.Id.NAME,
    // The information that stores the mapping information is a property.
    include = JsonTypeInfo.As.PROPERTY,
    // The property is called "type".
    property = "type"
)
@JsonSubTypes({
        @JsonSubTypes.Type(value = SpecializedElement1.class, name = "specializedElement1"),
        @JsonSubTypes.Type(value = SpecializedElement1.class, name = "specializedElement2")
})
public class Element {
    // ....
}

此控制器操作按预期工作...

@RequestMapping(value = "/create", method = RequestMethod.POST)
@ResponseBody
public Map<String, Object> create(@RequestBody Element element) {
    if (element == null) {
        // Return an error response.
    }
    try {
        return elementService.update(element);
    } catch (Exception e) {
        // Return an error response.
    }
}

...有了这个请求：

POST /create/
... more headers ...
Content-Type: application/json


{
    "type": "specializedElement1"
}

Spring-MVC，InheritanceType.JOINED，以及JSON对象与Jackson实体的自动映射

1 个答案: