Java JAXB 物件寫出為xml檔範例 write object to xml file example

Java使用JAXB(Java Architecture for XML Binding)將Java物件寫出為xml檔內的範例如下。

以下為要轉成xml檔的Java物件類別。

Employee

import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import java.util.Arrays;
import java.util.Date;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(propOrder = {"id", "name", "email", "age", "onBoardDate", "department", "exts"})
@XmlRootElement(name = "employee")
public class Employee {

    private int id;
    private String name;
    private String email;
    private int age;

    @XmlJavaTypeAdapter(DateAdapter.class)
    private Date onBoardDate;

    private Department department;

    @XmlElementWrapper(name = "exts")
    @XmlElement(name = "ext")
    private String[] exts;

    // getters and setters
}

xml內層元素的對應類別。

Department

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlType;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(propOrder = {"id", "name", "manager"})
public class Department {

    private int id;
    private String name;
    private Manager manager;

    // getters and setters
}

Manager

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlType;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(propOrder = {"id", "name", "email"})
public class Manager {

    private int id;
    private String name;
    private String email;

    // getters and setters
}

如果特定型態如日期Date要轉成指定格式，則自訂一個實作XmlAdapter的類別做為@XmlJavaTypeAdapter的參數並掛在要轉換的欄位上進行轉換。例如下面的DateAdapter。

DateAdapter

import javax.xml.bind.annotation.adapters.XmlAdapter;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateAdapter extends XmlAdapter<String, Date> {

    private static final String PATTERN = "yyyy-MM-dd";

    @Override
    public Date unmarshal(String v) throws Exception {
        return new SimpleDateFormat(PATTERN).parse(v);
    }

    @Override
    public String marshal(Date v) {
        return new SimpleDateFormat(PATTERN).format(v);
    }
}

轉換方式如下。

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import java.io.File;
import java.util.Date;

public class Main {

    private static final String XML_PATH = "src/main/resources/employee.xml";

    public static void main(String[] arges) throws JAXBException {

        Manager manager = new Manager();
        manager.setId(52);
        manager.setName("Mary");
        manager.setEmail("mary@abc.com");

        Department department = new Department();
        department.setId(22);
        department.setName("Marketing");
        department.setManager(manager);

        Employee employee = new Employee();
        employee.setId(100);
        employee.setName("John");
        employee.setEmail("john@abc.com");
        employee.setAge(29);
        employee.setOnBoardDate(new Date());
        employee.setDepartment(department);
        employee.setExts(new String[]{"201", "202"});

        JAXBContext jaxbContext = JAXBContext.newInstance(Employee.class);
        Marshaller marshaller = jaxbContext.createMarshaller();
        marshaller.marshal(employee, new File(XML_PATH));
    }

}

執行後會寫出employee.xml於專案的src/main/resources（此目錄必須存在）內容如下。

employee.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><employee><id>100</id><name>John</name><email>john@abc.com</email><age>29</age><onBoardDate>2021-04-27</onBoardDate><department><id>22</id><name>Marketing</name><manager><id>52</id><name>Mary</name><email>mary@abc.com</email></manager></department><exts><ext>201</ext><ext>202</ext></exts></employee>

重新排版整理如下。

employee.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<employee>
    <id>100</id>
    <name>John</name>
    <email>john@abc.com</email>
    <age>29</age>
    <onBoardDate>2021-04-27</onBoardDate>
    <department>
        <id>22</id>
        <name>Marketing</name>
        <manager>
            <id>52</id>
            <name>Mary</name>
            <email>mary@abc.com</email>
        </manager>
    </department>
    <exts>
        <ext>201</ext>
        <ext>202</ext>
    </exts>
</employee>

• Java JAXB 讀取xml檔為物件範例