如何将 XML 解组为对象

创建解组器

通常，要创建 Unmarshaller，我们可以重用此代码。

JAXBContext jaxbContext 	= JAXBContext.newInstance( Employee.class );
Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
//Overloaded methods to unmarshal from different xml sources
Employee employee = (Employee) jaxbUnmarshaller.unmarshal( xmlSource );

从 InputStream 解组

InputStream inStream = new FileInputStream( "employee.xml" );
Employee employee = (Employee) jaxbUnmarshaller.unmarshal( inStream );

从 URL 解组

URL url = new URL( "http://localhost:8080/employee.xml" );
Employee employee = (Employee) jaxbUnmarshaller.unmarshal( url );

解组字符串内容

String xmlString = "...";
Employee employee = (Employee) jaxbUnmarshaller.unmarshal(new StringReader(xmlString));

从 org.w3c.dom.Node 解组

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
DocumentBuilder db = dbf.newDocumentBuilder();
Document document = db.parse(new File( "employee.xml")); //Node
Employee employee = (Employee) jaxbUnmarshaller.unmarshal( document );

JAXB Unmarshaller接口负责管理将 XML 数据反序列化为 Java 对象的过程。
可以对各种输入源进行对象的解组。

JAXB 解组器示例

测试xml文件 employee.xml：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<employee>
    <department>
        <id>101</id>
        <name>IT</name>
    </department>
    <firstName>JackLi</firstName>
    <id>1</id>
    <lastName>Gupta</lastName>
</employee>

将 XML 文件解组为 Java Object

package com.onitroad.demo;
import java.io.File;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import com.onitroad.demo.model.Employee;
public class JaxbExample 
{
	public static void main(String[] args) 
	{
		String fileName = "employee.xml";
		jaxbXmlFileToObject(fileName);
	}
	private static void jaxbXmlFileToObject(String fileName) {

		File xmlFile = new File(fileName);

		JAXBContext jaxbContext;
		try 
		{
			jaxbContext = JAXBContext.newInstance(Employee.class);
			Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

			Employee employee = (Employee) jaxbUnmarshaller.unmarshal(xmlFile);

			System.out.println(employee);
		}
		catch (JAXBException e) 
		{
			e.printStackTrace();
		}
	}
}

JAXB 解组器属性

当前，Unmarshaller 上的所有 JAXB 提供程序都不需要支持任何属性。
但是，某些提供程序可能支持他们自己的一组特定于提供程序的属性。

解组器事件回调

我们可以通过在 JAXB 注释类中添加这些回调方法来自定义解组操作，例如

Employee.java。
我们需要定义两个方法，它们将在 Unmarshaller处理该类之前和之后进行侦听。

• void beforeUnmarshal(Unmarshaller unmarshaller, Object parent) {}
• void afterUnmarshal(Unmarshaller unmarshaller, Object parent) {}

package com.onitroad.demo.model;
import java.io.Serializable;
import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlRootElement;
@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
	@Override
	public String toString() {
		return "Employee [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", department="
				+ department + "]";
	}
	// It is called immediately after the object is created and before the unmarshalling begins.
	// The callback provides an opportunity to initialize JavaBean properties prior to unmarshalling.
	void beforeUnmarshal(Unmarshaller unmarshaller, Object parent) {
		System.out.println("Before Unmarshaller Callback");
	}
	// It is called after all the properties are unmarshalled for this object,
	// but before this object is set to the parent object.
	void afterUnmarshal(Unmarshaller unmarshaller, Object parent) {
		System.out.println("After Unmarshaller Callback");
	}
}