关于JAXB:

JAXB（Java Architecture for XML Binding) 是一个业界的标准，是一项可以根据XML Schema产生Java类的技术。该过程中，JAXB也提供了将XML实例文档反向生成Java对象树的方法，并能将Java对象树的内容重新写到XML实例文档。从另一方面来讲，JAXB提供了快速而简便的方法将XML模式绑定到Java表示，从而使得Java开发者在Java应用程序中能方便地结合XML数据和处理函数。

JAXB重要的类和接口：

JAXBContext类 是应用的入口，用来管理xml/java的绑定信息

Marshaller接口 其实现可将java object序列化成xml

Unmarshaller接口 其实现可将xml反序列化成java object

JAXB的annotation注解：

@XmlType，将Java类或枚举类型映射到XML模式类型，通常使用其propOrder属性指定字段，序列化的顺序，例如：

@XmlType（propOrder = {"studentId","studentName","country","courses" }）

注意：1.@XmlElementWrapper标注的属性，不能出现在@XmlType的propOrder列表中

2.所有@XmlElement标注过的属性，必须出现在@XmlType的propOrder列表中

@XmlAccessorType(XmlAccessType.FIELD) ，控制字段或属性的序列化。FIELD表示JAXB将自动绑定Java类中的每个非静态的（static）、非瞬态 的（由@XmlTransient标注）字段到XML。其他值还有XmlAccessType.PROPERTY和XmlAccessType.NONE。

@XmlAccessorOrder，控制JAXB 绑定类中属性和字段的排序，有两个选项：

XmlAccessOrder.ALPHABETICAL

XmlAccessOrder.UNDEFINED

@XmlJavaTypeAdapter，使用定制的适配器（即扩展抽象类XmlAdapter并覆盖marshal()和unmarshal()方法），以序列化Java类为XML。

@XmlElementWrapper ，对于数组或集合（即包含多个元素的成员变量），生成一个包装该数组或集合的XML元素（称为包装器）。

@XmlRootElement，将Java类或枚举类型映射到XML元素。

@XmlElement，将Java类的一个属性映射到与属性同名的一个XML元素。

@XmlAttribute，将Java类的一个属性映射到与属性同名的一个XML属性。

以上是关于JAXB的介绍，接下来看个实例：

//学生类，其中嵌套了课程类CourseDO的list成员变量

@XmlRootElement(name = "Student")
@XmlAccessorType(XmlAccessType.FIELD)
public class StudentDO {
public Integer getStudentId() {
return studentId;
}
public void setStudentId(Integer studentId) {
this.studentId = studentId;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}

public List<CourseDO> getCourses() {
return courses;
}
public void setCourses(List<CourseDO> courses) {
this.courses = courses;
}

@XmlElement(name = "StudentId")
Integer studentId;
@XmlElement(name = "StudentName")
public String studentName;
@XmlElement(name = "Country")
String country;
@XmlElementWrapper(name = "courselist")
@XmlElement(name = "course")
List<CourseDO> courses;
}

// CourseDO类

@XmlAccessorType(XmlAccessType.FIELD)
public class CourseDO {
public String getCourseId() {
return courseId;
}
public void setCourseId(String courseId) {
this.courseId = courseId;
}
public String getCourseName() {
return courseName;
}
public void setCourseName(String courseName) {
this.courseName = courseName;
}
public String getScope() {
return scope;
}
public void setScope(String scope) {
this.scope = scope;
}


@XmlElement(name = "CourseId")
String courseId;
@XmlElement(name = "CourseName")
String courseName;
@XmlElement(name = "Scope")
String scope;
}

//JAXB的封装类

public class JAXBUtil {
private static Map<Class<?>,JAXBContext> contextClassMap = new ConcurrentHashMap<Class<?>,JAXBContext>();
public static JAXBContext getContext(Class<?> type) throws JAXBException {
JAXBContext context = contextClassMap.get(type);
if(context == null){
context = JAXBContext.newInstance(type);
contextClassMap.put(type,context);
}
return context;
}
public static String toXml(Object obj) throws Exception {
StringWriter writer = new StringWriter();
JAXBContext context = getContext(obj.getClass());
Marshaller marshaller = context.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT,true);
marshaller.setProperty(Marshaller.JAXB_ENCODING,"UTF-8");
marshaller.setProperty(Marshaller.JAXB_FRAGMENT,false);
marshaller.marshal(obj,writer);
return writer.toString();
}
public static Object fromXml(String xml,Class<?> type) throws Exception {
StringReader reader = new StringReader(xml);
JAXBContext context = getContext(type);
Unmarshaller unmarshaller = context.createUnmarshaller();
Object obj = type.cast(unmarshaller.unmarshal(reader));
return obj;
}
}

//序列化的测试方法

@Test
public void testToXml() throws Exception {
try{
StudentDO student = new StudentDO();
student.setStudentId(0);
student.setStudentName("lily");
student.setCountry("USA");
student.setCourses(getCourseList());
String xml = JAXBUtil.toXml(student);
System.out.println(xml);
}catch (Exception e){
System.out.println(e.getMessage());
}
}

输出结果：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Student>
<StudentId>0</StudentId>
<StudentName>lily</StudentName>
<Country>USA</Country>
<courselist>
<course>
<CourseId>000</CourseId>
<CourseName>Physic</CourseName>
<Scope>Science</Scope>
</course>
<course>
<CourseId>001</CourseId>
<CourseName>Music</CourseName>
<Scope>Art</Scope>
</course>
</courselist>
</Student>

//反序列化的测试方法

@Test

public void testFromXml() throws Exception {
    String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?><Student><StudentId>0</StudentId><StudentName>lily</StudentName><Country>USA</Country><Course><CourseId>000</CourseId><CourseName>Physic</CourseName><Scope>Science</Scope></Course><Course><CourseId>001</CourseId><CourseName>Music</CourseName><Scope>Art</Scope></Course><Course><CourseId>002</CourseId><CourseName>Math</CourseName><Scope>Science</Scope></Course></Student>";
    try{
        StudentDO student = (StudentDO)JAXBUtil.fromXml(xml,StudentDO.class);
        int ac = @H_924_502@0;
        int dd = ac + @H_924_502@1;
    }catch (Exception e){
        System.out.println(e.getMessage());
    }
}