JAXB Marshaller（编组器）示例 · HowToDoInJava 中文系列教程

# JAXB `Marshaller`（编组器）示例 > 原文： [https://howtodoinjava.com/jaxb/marshaller-example/](https://howtodoinjava.com/jaxb/marshaller-example/) JAXB [`Marshaller`](https://docs.oracle.com/javase/10/docs/api/javax/xml/bind/Marshaller.html)接口负责管理将 Java 内容树即 **Java 对象转换为 XML** 数据的过程。可以将 XML 编组到各种输出目标。 ## 1\. JAXB 编组对象到 XML #### 1.1 创建编组器通常，要创建编组器，可以重用此代码。 ```java JAXBContext jaxbContext = JAXBContext.newInstance( Employee.class ); Marshaller jaxbMarshaller = jaxbContext.createMarshaller(); Employee employeeObj = new Employee(1, "Lokesh", "Gupta", new Department(101, "IT")); //Overloaded methods to marshal to different outputs jaxbMarshaller.marshal(employeeObj); ``` #### 1.2 编组 XML 文件 ```java OutputStream os = new FileOutputStream( "employee.xml" ); jaxbMarshaller.marshal( employeeObj, os ); ``` #### 1.3 编组至 SAX `ContentHandler` 假设`MyContentHandler`是 [`org.xml.sax.ContentHandler`](https://docs.oracle.com/javase/7/docs/api/org/xml/sax/ContentHandler.html) 的实例。 ```java jaxbMarshaller.marshal( employeeObj, new MyContentHandler() ); ``` #### 1.4 编组 DOM 文件 ```java DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); dbf.setNamespaceAware(true); DocumentBuilder db = dbf.newDocumentBuilder(); Document doc = db.newDocument(); jaxbMarshaller.marshal( employeeObj, doc ); ``` #### 1.5 编组并打印到控制台 ```java m.marshal( employeeObj, new PrintWriter( System.out ) ); ``` ## 2\. JAXB `Marshaller`属性 ```java jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE); //or jaxbMarshaller.setProperty("jaxb.formatted.output", Boolean.TRUE); ``` 所有 JAXB 供应器都必须支持以下属性集。一些供应器可能支持其他属性。 * **`jaxb.encoding`** - 编组 XML 数据时使用的输出编码。如果未指定此属性，则默认情况下`Marshaller`将使用“`UTF-8`”。 * **`jaxb.formatted.output`** - 值可以是`true`或`false`。 `Marshaller`是否将使用换行符和缩进来格式化所得的 XML 数据。默认值为`false`。 * **`jaxb.schemaLocation`** – 允许客户端应用在生成的 XML 数据中指定`xsi:schemaLocation`属性。 * **`jaxb.noNamespaceSchemaLocation`** – 它允许客户端应用在生成的 XML 数据中指定`xsi:noNamespaceSchemaLocation`属性。 * **`jaxb.fragment`** – 它确定`Marshaller`是否将生成文档级事件。值可以是`true`或`false`。 ## 3.`Marshaller`回调方法您可以通过 JAXB 注解类中的**自定义编组操作**，例如 `Employee.java`。您需要定义两个方法，这些方法将在编组程序处理该类之前和之后进行监听。在这些方法中，您可以执行诸如设置额外字段之类的操作。 ```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 + "]"; } // Invoked by Marshaller after it has created an instance of this object. boolean beforeMarshal(Marshaller marshaller) { System.out.println("Before Marshaller Callback"); return true; } // Invoked by Marshaller after it has marshalled all properties of this object. void afterMarshal(Marshaller marshaller) { System.out.println("After Marshaller Callback"); } } ``` ## 4\. JAXB 编组示例 **将 Java 对象编组为 XML 字符串**的示例。 ```java package com.howtodoinjava.demo; import java.io.StringWriter; import javax.xml.bind.JAXBContext; import javax.xml.bind.JAXBException; import javax.xml.bind.Marshaller; 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")); jaxbObjectToXML(employee); } private static void jaxbObjectToXML(Employee employee) { try { JAXBContext jaxbContext = JAXBContext.newInstance(Employee.class); Marshaller jaxbMarshaller = jaxbContext.createMarshaller(); jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE); // To format XML //Print XML String to Console jaxbMarshaller.marshal(employee, System.out); } catch (JAXBException e) { e.printStackTrace(); } } } ``` 程序输出。 ```java Before Marshaller Callback After Marshaller Callback <?xml version="1.0" encoding="UTF-8"?> <employee> <department> <id>101</id> <name>IT</name> </department> <firstName>Lokesh</firstName> <id>1</id> <lastName>Gupta</lastName> </employee> ``` 将我的问题放在评论部分。学习愉快！