JAX-RS Jersey JSON使用注释保留null [英] JAX-RS Jersey JSON preserve null using annotations

问题描述

当接收包含null或值的JSON sting时，如何让JAXB保留空值。

How do I have JAXB preserve nulls when receiving a JSON sting that contains a null or "" value.

字符串： {id：null，fname：John，region：}

返回对象：

 Person {
    Integer id = 0
    String fname = "John"
    Region regions = 0 }

我希望它返回null而不是0

I would like it to return null instead of 0

这是我到目前为止所拥有的：

Here is what I have so far:

@Provider
public class JAXBContextResolver implements ContextResolver<JAXBContext> {
    private JAXBContext context;
    private Class<?>[] types = {Person.class};

    public JAXBContextResolver() throws Exception {
        this.context = new JSONJAXBContext(JSONConfiguration.natural().build(), types);
    }

    public JAXBContext getContext(Class<?> objectType) {
        for (Class<?> c : types) {
            if (c.equals(objectType)) {
                return context;
            }
        }
        return null;
    }
}

Person.class用 @XmlRootElement 我试过调查杰克逊注释但没有成功。

Person.class is annotated with @XmlRootElement I've tried looking into Jackson annotations but have had no success.

推荐答案

注意：我是 EclipseLink JAXB（MOXy） 领导和 JAXB（JSR-222） 专家组。

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

以下是使用MOXy如何完成此操作的示例。

Below is an example of how this can be done with MOXy.

人

MOXy将根据需要解组 Person 对象，而不指定任何元数据。要使输出JSON包含空值，可以使用 @XmlElement（nillable = true）注释（请参阅绑定到JSON和XML - 处理空值）。

MOXy will unmarshal the Person object as you want without specifying any metadata. To have the output JSON contain null values, you can use the @XmlElement(nillable=true) annotation (see Binding to JSON & XML - Handling Null).

package forum8748537;

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    @XmlElement(nillable=true)
    Integer id;

    @XmlElement(nillable=true)
    String fname;

    @XmlElement(nillable=true)
    Region regions;

}

jaxb.properties

要将MOXy指定为JAXB（JSR-222）提供程序，您需要在其中添加名为 jaxb.properties 的文件。与包含以下条目的域类相同的包（请参阅指定EclipseLink MOXy作为您的JAXB提供程序）。

To specify MOXy as your JAXB (JSR-222) provider you need to add a file called jaxb.properties in the same package as your domain classes with the following entry (see Specifying EclipseLink MOXy as Your JAXB Provider).

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

演示

package forum8748537;

import java.io.StringReader;
import java.util.*;

import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;

public class Demo {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(2);
        properties.put("eclipselink.media-type", "application/json");
        properties.put("eclipselink.json.include-root", false);
        JAXBContext jc = JAXBContext.newInstance(new Class[] {Person.class}, properties);

        StringReader json = new StringReader("{\"id\":null,\"fname\":\"John\",\"region\":\"\"}");
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        Person person = unmarshaller.unmarshal(new StreamSource(json), Person.class).getValue();

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(person, System.out);
    }

}

输出

{
   "id" : null,
   "fname" : "John",
   "regions" : null
}

在JAX中使用MOXy- RS应用程序

有关在JAX-RS应用程序中使用MOXy的示例，请参阅：

For an example of using MOXy in a JAX-RS application see:

• MOXy as您的JAX-RS JSON提供程序 - 服务器端


• MOXy作为您的JAX-RS JSON提供商 - 客户端

• MOXy as Your JAX-RS JSON Provider - Server Side
• MOXy as Your JAX-RS JSON Provider - Client Side

这篇关于JAX-RS Jersey JSON使用注释保留null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！