# JAXB `Unmarshaller`（解组器）示例 > 原文： [https://howtodoinjava.com/jaxb/jaxb-unmarshaller-example/](https://howtodoinjava.com/jaxb/jaxb-unmarshaller-example/) JAXB [`Unmarshaller`](https://docs.oracle.com/javase/10/docs/api/javax/xml/bind/Unmarshaller.html)接口负责管理将 XML 数据反序列化为 Java 对象的过程。 可以将对象解组到各种输入源。 ## 1.如何将 XML 解组到对象 #### 1.1 创建解组器 通常，要创建`Unmarshaller`，可以重用此代码。 ```java JAXBContext jaxbContext = JAXBContext.newInstance( Employee.class ); Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller(); //Overloaded methods to unmarshal from different xml sources Employee employee = (Employee) jaxbUnmarshaller.unmarshal( xmlSource ); ``` #### 1.2 从`InputStream`解组 ```java InputStream inStream = new FileInputStream( "employee.xml" ); Employee employee = (Employee) jaxbUnmarshaller.unmarshal( inStream ); ``` #### 1.3 从 URL 解组 ```java URL url = new URL( "http://localhost:8080/employee.xml" ); Employee employee = (Employee) jaxbUnmarshaller.unmarshal( url ); ``` #### 1.4 解组字符串内容 ```java String xmlString = "..."; Employee employee = (Employee) jaxbUnmarshaller.unmarshal(new StringReader(xmlString)); ``` #### 1.5 从`org.w3c.dom.Node`解组 ```java 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 ); ``` ## 2\. JAXB 解组器属性 当前，`Unmarshaller`上的所有 JAXB 供应器都不需要**所有属性**。 但是，某些供应器可能支持它们自己的一组供应器特定属性。 ## 3.解组事件回调 您可以通过在 [JAXB 注解的](https://howtodoinjava.com/jaxb/jaxb-annotations/)类中添加这些回调方法**来自定义解组操作**，例如`Employee.java`。 您需要定义两个方法，这些方法将在`Unmarshaller`处理该类之前和之后监听。 * `void beforeUnmarshal(Unmarshaller unmarshaller, Object parent) {}` * `void afterUnmarshal(Unmarshaller unmarshaller, Object parent) {}` ```java package com.howtodoinjava.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"); } } ``` ## 4\. JAXB 解组器示例 **将 XML 文件解组到 Java 对象**的示例。 ```java package com.howtodoinjava.demo; import java.io.File; import javax.xml.bind.JAXBContext; import javax.xml.bind.JAXBException; import javax.xml.bind.Unmarshaller; import com.howtodoinjava.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(); } } } ``` 程序输出。 ```java Before Unmarshaller Callback After Unmarshaller Callback Employee [id=1, firstName=Lokesh, lastName=Gupta, department=Department [id=101, name=IT]] ``` 其中`employee.xml`文件是： ```java <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <employee> <department> <id>101</id> <name>IT</name> </department> <firstName>Lokesh</firstName> <id>1</id> <lastName>Gupta</lastName> </employee> ``` 向我提出您的有关使用 JAXB 注解在 Java 中解组的问题。 学习愉快！