JAXB 将对象转换为 JSON 的示例

1. MOXy 依赖
2. Java 对象到 JSON 字符串
3. Java 对象到 JSON 文件

原文： https://howtodoinjava.com/jaxb/convert-object-to-json-moxy/

Java 示例将 Java 对象转换为 JSON 字符串或将 JSON 写入文件。本示例将 MOXy 与 JAXB 一起使用，以将 Java 对象编组为 JSON。 MOXy 实现 JAXB，使开发人员可以通过注解提供其映射信息，并提供 JAXB 默认不提供的许多丰富功能。

1. MOXy 依赖

包括 MOXy 到项目运行时。

<dependency>
    <groupId>org.eclipse.persistence</groupId>
    <artifactId>org.eclipse.persistence.moxy</artifactId>
    <version>2.5.2</version>
</dependency>

2. Java 对象到 JSON 字符串

2.1 添加 JAXB 注解

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.PROPERTY)
public class Employee implements Serializable {
    private static final long serialVersionUID = 1L;
    private Integer id;
    private String firstName;
    private String lastName;
    private Department department;
    public Employee() {
        super();
    }
    //Setters and Getters
}

@XmlRootElement(name = "department")
@XmlAccessorType(XmlAccessType.PROPERTY)
public class Department implements Serializable {
    private static final long serialVersionUID = 1L;
    Integer id;
    String name;
    public Department() {
        super();
    }
    //Setters and Getters
}

2.2 添加`jaxb.properties`

当您获得JAXBContext的实例时，JAXB 将检查jaxb.properties文件并构造上下文。在这里，您从 MOXy 库中注入了JAXBContextFactory。

将jaxb.properties文件放在放置 JAXB 注解类的同一包中。

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

2.3 将对象转换为 JSON

现在使用javax.xml.bind.Marshaller类将对象转换为 json。

package com.howtodoinjava.demo;
import java.io.StringWriter;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import org.eclipse.persistence.jaxb.MarshallerProperties;
import com.howtodoinjava.demo.model.Department;
import com.howtodoinjava.demo.model.Employee;
public class JaxbExample 
{
    public static void main(String[] args) 
    {
        Employee employee = new Employee(1, "Lokesh", "Gupta", new Department(101, "IT"));
        jaxbObjectToJSON(employee);
    }
    private static void jaxbObjectToJSON(Employee employee) 
    {
        try 
        {
            JAXBContext jaxbContext = JAXBContext.newInstance(Employee.class);
            Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
            // To format JSON
            jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE); 
            //Set JSON type
            jaxbMarshaller.setProperty(MarshallerProperties.MEDIA_TYPE, "application/json");
            jaxbMarshaller.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, true);
            //Print JSON String to Console
            StringWriter sw = new StringWriter();
            jaxbMarshaller.marshal(employee, sw);
            System.out.println(sw.toString());
        } 
        catch (JAXBException e) 
        {
            e.printStackTrace();
        }
    }
}

程序输出：

{
   "employee" : {
      "department" : {
         "id" : 101,
         "name" : "IT"
      },
      "firstName" : "Lokesh",
      "id" : 1,
      "lastName" : "Gupta"
   }
}

阅读更多：将 Java 对象转换为 XML

3. Java 对象到 JSON 文件

使用上面的代码，现在输出到 json 文件。

package com.howtodoinjava.demo;
import java.io.File;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import org.eclipse.persistence.jaxb.MarshallerProperties;
import com.howtodoinjava.demo.model.Department;
import com.howtodoinjava.demo.model.Employee;
public class JaxbExample 
{
    public static void main(String[] args) 
    {
        Employee employee = new Employee(1, "Lokesh", "Gupta", new Department(101, "IT"));
        jaxbObjectToJSON(employee);
    }
    private static void jaxbObjectToJSON(Employee employee) 
    {
        try 
        {
            JAXBContext jaxbContext = JAXBContext.newInstance(Employee.class);
            Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
            // To format JSON
            jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE); 
            //Set JSON type
            jaxbMarshaller.setProperty(MarshallerProperties.MEDIA_TYPE, "application/json");
            jaxbMarshaller.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, true);
             //Store JSON to File
            File file = new File("employee.json");
            jaxbMarshaller.marshal(employee, file);
        } 
        catch (JAXBException e) 
        {
            e.printStackTrace();
        }
    }
}