在项目中经常会遇到xml与Object的转换，即java对象序列号为xml文档，xml文档可以反序列化为java对象。目前比较好用的有jaxb和XStream。下面进行分别介绍
一、JAXB
Java Architecture for XML Binding (JAXB) 是一个业界的标准，是一项可以根据XML Schema产生Java类的技术。
废话不多说，直接上例子，假设我们需要实现一个简单的学校学生系统，我们的java对象如下：
/**
* @author ozl
* 基类
*/
public abstract class AbstracElement {
private String address;
private String name;
/**
* @return the address
*/
public String getAddress() {
return address;
}
/**
* @param address the address to set
*/
public void setAddress(String address) {
this.address = address;
}
/**
* @return the name
*/
public String getName() {
return name;
}
/**
* @param name the name to set
*/
public void setName(String name) {
this.name = name;
}
}
//学生对象
public class Student extends AbstracElement {
// 出生日期
private XMLGregorianCalendar birthDay;
/**
* @return the birthDay
*/
public XMLGregorianCalendar getBirthDay() {
return birthDay;
}
/**
* @param birthDay
* the birthDay to set
*/
public void setBirthDay(XMLGregorianCalendar birthDay) {
this.birthDay = birthDay;
}
}
public class School extends AbstracElement {
private List<Student> students;
private int studentCount;
/**
* @return the students
*/
public List<Student> getStudents() {
return students;
}
/**
* @return the studentCount
*/
public int getStudentCount() {
studentCount=getStudents().size();
return this.studentCount;
}
}
jaxb通过注解的关联java对象和序列号的方式，现在我们着重介绍一下常用的xml.binding提供的注解。
@XmlAccessorType 控制默认序列号使用javabean的属性或者字段，值为XmlAccessType类型，当为PROPERTY时表示每一个setter/getter方法对都是序列号、FIELD表示字段、PUBLIC_MEMBER表示FIELD或者getter/setter方法。
@XmlRootElement：映射xml的根节点，name和namespace方法
@XmlElement：表示一个子节点，里面可以有name和namespace方法
@XmlAttribute：表示属性。
现在我们在上面的java代码上就可以使用上面的注解实现序列化了。
我们在基类AbstracElement中把name作为节点的属性，在address作为字元素处理，代码如下：
/**
* @return the address
*/
@XmlElement(name="address",namespace=JaxbTest.default_namespace)
public String getAddress() {
return address;
}
/**
* @return the name
*/
@XmlAttribute
public String getName() {
return name;
}
修改School类如下：
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name="school",namespace=JaxbTest.default_namespace) //定义根节点的名字和命名空间
public class School extends AbstracElement {
@XmlElement(name="student",namespace=JaxbTest.default_namespace )
private List<Student> students;
//其他的方法省略了
}
@XmlAccessorType(XmlAccessType.PROPERTY)
public class Student extends AbstracElement {
// 出生日期
// @XmlElement //如果此时再加上这个注解就会报错，发现两个birthDay属性
private XMLGregorianCalendar birthDay;
/**
* @return the birthDay
*/
@XmlElement(namespace = JaxbTest.default_namespace)
public XMLGregorianCalendar getBirthDay() {
return birthDay;
}
//省略了其他的方法
｝
我们的测试代码如下：
public class JaxbTest {
public static final String default_namespace = "http://www.ozl.com/test.default";
public static final String extend_namespace = "http://www.ozl.com/test.extend";
/**
* @param args
* @throws JAXBException
* @throws DatatypeConfigurationException
*/
public static void main(String[] args) throws JAXBException,
DatatypeConfigurationException {
marshallerXML();
unmarshaller();
}
public static void marshallerXML() throws JAXBException,
DatatypeConfigurationException {
JAXBContext jc = JAXBContext.newInstance(School.class);
School school = new School();
school.setName("实验");
school.setAddress("南京雨花台区");
List<Student> students = new ArrayList<>();
school.setStudents(students);
Student student1 = new Student();
student1.setName("张三");
student1.setAddress("南京市xx路");
XMLGregorianCalendar c = DatatypeFactory.newInstance()
.newXMLGregorianCalendarDate(2014, 11, 11,
DatatypeConstants.FIELD_UNDEFINED);
student1.setBirthDay(c);
students.add(student1);
Student student2 = new Student();
student2.setName("李四");
student2.setAddress("济南市xx路");
students.add(student2);
Student student3 = new Student();
student3.setName("王五");
student3.setAddress("济南市xx路");
students.add(student3);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.setProperty(Marshaller.JAXB_ENCODING, "GBK");
marshaller.marshal(school, System.out);
}
public static void unmarshaller() throws JAXBException {
InputStream io = JaxbTest.class.getResourceAsStream("school.xml");
JAXBContext jc = JAXBContext.newInstance(School.class);
Unmarshaller unmarshaller = jc.createUnmarshaller();
School school = (School) unmarshaller.unmarshal(io);
System.out.println(school.getStudentCount());
}
}
输出结果为：
<?xml version="1.0" encoding="GBK" standalone="yes"?>
<school name="实验" xmlns="http://www.ozl.com/test.default">
<address>南京雨花台区</address>
<student name="张三">
<address>南京市xx路</address>
<birthDay>2014-11-11</birthDay>
</student>
<student name="李四">
<address>济南市xx路</address>
</student>
<student name="王五">
<address>济南市xx路</address>
</student>
</school>
现在我需要在student的子节点上包装一层节点，需要使用@XmlElementWrapper注解，Student类的students字段上增加如下注解：
@XmlElementWrapper(name="students",namespace=JaxbTest.default_namespace ) //多包一层节点 @XmlElement(name="student",namespace=JaxbTest.default_namespace ) private List<Student> students;
如果此时再运行我们的测试代码，输出如下：
<?xml version="1.0" encoding="GBK" standalone="yes"?>
<school name="实验" xmlns="http://www.ozl.com/test.default">
<address>南京雨花台区</address>
<students>
<student name="张三">
<address>南京市xx路</address>
<birthDay>2014-11-11</birthDay>
</student>
<student name="李四">
<address>济南市xx路</address>
</student>
<student name="王五">
<address>济南市xx路</address>
</student>
<students>
</school>
现在我需要记录学生的兴趣爱好，在Student类上增加List<String> hobbies字段。我们修改测试代码和Student类如下：
// 星期爱好
private List<String> hobbies;
@XmlElement(name="hobby" ,namespace=JaxbTest.default_namespace) //自定义节点的名字
public List<String> getHobbies() {
return hobbies;
}
修改测试代码的marshallerXML()方法如下：
JAXBContext jc = JAXBContext.newInstance(School.class);
School school = new School();
school.setName("实验");
school.setAddress("南京雨花台区");
List<Student> students = new ArrayList<>();
school.setStudents(students);
Student student1 = new Student();
student1.setName("张三");
student1.setAddress("南京市xx路");
List<String> hobbies = new ArrayList<>();
hobbies.add("游泳");
hobbies.add("乒乓球");
student1.setHobbies(hobbies);
XMLGregorianCalendar c = DatatypeFactory.newInstance()
.newXMLGregorianCalendarDate(2014, 11, 11,
DatatypeConstants.FIELD_UNDEFINED);
student1.setBirthDay(c);
students.add(student1);
Student student2 = new Student();
student2.setName("李四");
student2.setAddress("济南市xx路");
hobbies = new ArrayList<>(hobbies);
hobbies.add(0, "篮球");
student2.setHobbies(hobbies);
students.add(student2);
Student student3 = new Student();
student3.setName("王五");
student3.setAddress("济南市xx路");
hobbies = new ArrayList<>(hobbies);
hobbies.remove(1);
student3.setHobbies(hobbies);
students.add(student3);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.setProperty(Marshaller.JAXB_ENCODING, "GBK");
marshaller.marshal(school, System.out);
测试结果如下：
<?xml version="1.0" encoding="GBK" standalone="yes"?>
<school name="实验" xmlns="http://www.ozl.com/test.default">
<address>南京雨花台区</address>
<students>
<student name="张三">
<address>南京市xx路</address>
<birthDay>2014-11-11</birthDay>
<hobby>游泳</hobby>
<hobby>乒乓球</hobby>
</student>
<student name="李四">
<address>济南市xx路</address>
<hobby>篮球</hobby>
<hobby>游泳</hobby>
<hobby>乒乓球</hobby>
</student>
<student name="王五">
<address>济南市xx路</address>
<hobby>篮球</hobby>
<hobby>乒乓球</hobby>
</student>
</students>
</school>
发现hobby列了很多子节点，但是我需要序列号为一个节点，这时候可以使用@XmlJavaTypeAdapter来实现自己序列号或者反序列化的规则，现在修改如下：
/**
* @return the hobbies
*/
@XmlJavaTypeAdapter(ListXmlAdapter.class) //自定义序列号和反序列化方式
@XmlElement(name="hobby" ,namespace=JaxbTest.default_namespace) //自定义节点的名字
public List<String> getHobbies() {
return hobbies;
}
而ListXmlAdapter类如下：
/**
* @author ozl
*
*/
public class ListXmlAdapter extends XmlAdapter<String, List<String>> {
@Override
public List<String> unmarshal(String v) throws Exception {
String[] values = v.split("#");
return new ArrayList<String>(Arrays.asList(values));
}
@Override
public String marshal(List<String> v) throws Exception {
StringBuffer buffer=new StringBuffer();
for(int i=0;i<v.size()-1;i++)
{
buffer.append(v.get(i));
buffer.append("#");
}
if(v.size()>0)
{
buffer.append(v.get(v.size()-1));
}
return buffer.toString();
}
}
此时再运行我们的测试代码，得到的结果如下：
<?xml version="1.0" encoding="GBK" standalone="yes"?>
<school name="实验" xmlns="http://www.ozl.com/test.default">
<address>南京雨花台区</address>
<students>
<student name="张三">
<address>南京市xx路</address>
<birthDay>2014-11-11</birthDay>
<hobby>游泳#乒乓球</hobby>
</student>
<student name="李四">
<address>济南市xx路</address>
<hobby>篮球#游泳#乒乓球</hobby>
</student>
<student name="王五">
<address>济南市xx路</address>
<hobby>篮球#乒乓球</hobby>
</student>
</students>
</school>
控制序列号的顺序：有的时候我们的xml可能是要符合一定的XSD的，需要指定顺序，@XmlType可以满足我们的要求，
@XmlType(name = "StudentType", namespace = JaxbTest.default_namespace, propOrder = { "hobbies" ,"birthDay"}) // propOrder表示元素系列化的顺序。不能包括父类的字段
有的时候我们需要添加一些扩展的元素和属性。 首先看一下如何添加扩展的属性，我们使用@XmlAnyAttribute注解实现，该注解作用的类型必须为Map<QName, String>类型，我们在School中增加 @XmlAnyAttribute //只要定义扩展属性，在xsd中为anyAttribute类型 private Map<QName, String> addationInfo; 修改测试代码如下：
public static void marshallerXML() throws JAXBException,
DatatypeConfigurationException {
JAXBContext jc = JAXBContext.newInstance(School.class);
School school = new School();
school.setName("实验");
school.setAddress("南京雨花台区");
Map<QName, String> schoolAddation = new HashMap<QName, String>();
QName nameQname = new QName(extend_namespace, "nature", "extend");
schoolAddation.put(nameQname, "公立");
school.setAddationInfo(schoolAddation);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.setProperty(Marshaller.JAXB_ENCODING, "GBK");
marshaller.marshal(school, System.out);
}
测试结果如下：
<?xml version="1.0" encoding="GBK" standalone="yes"?>
<school name="实验" extend:nature="公立" xmlns="http://www.ozl.com/test.default" xmlns:extend="http://www.ozl.com/test.extend">
<address>南京雨花台区</address>
</school>
@XmlAnyElement定义我们可以扩展元素： 我们在School类中增加如下字段： @XmlAnyElement private List<Object> anyExtendElements; 同时需要在school中增加一个校长的子节点，起java类如下：
@XmlRootElement(name="principal",namespace=JaxbTest.extend_namespace)
public class Principal extends AbstracElement {
private String description;
/**
* @return the description
*/
@XmlElement
public String getDescription() {
return description;
}
/**
* @param description the description to set
*/
public void setDescription(String description) {
this.description = description;
}
}
此时，我们需要定义个xmlFactory来识别这个类
@XmlRegistry
public class ObjectFactory {
@XmlElementDecl(name="principal",namespace=JaxbTest.extend_namespace)
public JAXBElement<Principal> createPrincipal(Principal principal) {
return new JAXBElement<Principal>(new QName("principal"),
Principal.class, principal);
}
}
修改测试代码如下：
public static void marshallerXML() throws JAXBException,
DatatypeConfigurationException {
JAXBContext jc = JAXBContext.newInstance(School.class,
ObjectFactory.class);
School school = new School();
school.setName("实验");
school.setAddress("南京雨花台区");
Principal p = new Principal();
p.setName("ozl");
school.getAnyExtendElements().add(p);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.setProperty(Marshaller.JAXB_ENCODING, "GBK");
marshaller.marshal(school, System.out);
}
测试结果如下：
<?xml version="1.0" encoding="GBK" standalone="yes"?>
<ns2:school name="实验" xmlns:ns2="http://www.ozl.com/test.default" xmlns:ns3="http://www.ozl.com/test.extend">
<ns2:address>南京雨花台区</ns2:address>
<ns3:principal name="ozl"/>
</ns2:school>
这样就是用jaxb实现了xml和java对象之间的转换
二、XStream xStream
可以轻易的将Java对象和xml文档相互转换，而且也支持json的转换。我们仍然用School模型来简要介绍XStream。
public abstract class AbstracElement {
private String address;
private String name;
/**
* @return the address
*/
public String getAddress() {
return address;
}
/**
* @param address the address to set
*/
public void setAddress(String address) {
this.address = address;
}
/**
* @return the name
*/
@XmlAttribute
public String getName() {
return name;
}
/**
* @param name the name to set
*/
public void setName(String name) {
this.name = name;
}
}
public class Student extends AbstracElement {
// 出生日期
private XMLGregorianCalendar birthDay;
// 星期爱好
private List<String> hobbies;
/**
* @return the birthDay
*/
public XMLGregorianCalendar getBirthDay() {
return birthDay;
}
/**
* @param birthDay
* the birthDay to set
*/
public void setBirthDay(XMLGregorianCalendar birthDay) {
this.birthDay = birthDay;
}
/**
* @return the hobbies
*/
public List<String> getHobbies() {
return hobbies;
}
/**
* @param hobbies
* the hobbies to set
*/
public void setHobbies(List<String> hobbies) {
this.hobbies = hobbies;
}
}
public class School extends AbstracElement {
private List<Student> students;
private int studentCount;
/**
* @return the students
*/
public List<Student> getStudents() {
return students;
}
/**
* @param students
* the students to set
*/
public void setStudents(List<Student> students) {
this.students = students;
}
/**
* @return the studentCount
*/
public int getStudentCount() {
studentCount = getStudents().size();
return this.studentCount;
}
}
public class XStreamTest {
/**
* @param args
* @throws DatatypeConfigurationException
*/
public static void main(String[] args) throws DatatypeConfigurationException {
XStream xstream = new XStream(); //默认构造函数需要xpp.jar
xstream.alias("school", School.class);
xstream.alias("student", Student.class);
xstream.toXML(createStudent(), System.out);
}
public static School createStudent() throws DatatypeConfigurationException
{
School school=new School();
school.setName("实验");
school.setAddress("南京雨花台区");
List<Student> students=new ArrayList<Student>();
Student student1=new Student();
student1.setName("张三");
student1.setAddress("南京市xx路");
List<String> hobbies = new ArrayList<>();
hobbies.add("游泳");
hobbies.add("乒乓球");
student1.setHobbies(hobbies);
XMLGregorianCalendar c = DatatypeFactory.newInstance()
.newXMLGregorianCalendarDate(2014, 11, 11,
DatatypeConstants.FIELD_UNDEFINED);
student1.setBirthDay(c);
students.add(student1);
school.setStudents(students);
return school;
}
}
这样输入的结果如下：
<school>
<address>南京雨花台区</address>
<name>实验</name>
<students>
<student>
<address>南京市xx路</address>
<name>张三</name>
<birthDay class="com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl">
<year>2014</year>
<month>11</month>
<day>11</day>
<timezone>-2147483648</timezone>
<hour>-2147483648</hour>
<minute>-2147483648</minute>
<second>-2147483648</second>
</birthDay>
<hobbies>
<string>游泳</string>
<string>乒乓球</string>
</hobbies> </student>
</students>
<studentCount>0</studentCount>
</school>
此时我们不需要实例化school的studentCount属性，我们可以在测试代码中添加如下代码：
xstream.omitField(School.class, "studentCount");//表示序列号忽略该字段，也可以通过注解@XStreamOmitField
Xstream默认对List类型多了一层包装，我们可以通过修改如下代码来去掉<students>包装：
xstream.addImplicitCollection(School.class, "students");
而我同时需要把name字段作为一个属性输出，我们可以添加测试代码如下： xstream.useAttributeFor(AbstracElement.class, "name");
同样hobbies我们需要实例化一个节点，这个时候我们得提供自定义的序列化方式 xstream.registerLocalConverter(Student.class, "hobbies", new ListXmlConverter()); 其中ListXmlConverter类的代码如下：
public class ListXmlConverter implements SingleValueConverter {
/* (non-Javadoc)
* @see com.thoughtworks.xstream.converters.ConverterMatcher#canConvert(java.lang.Class)
*/
@Override
public boolean canConvert(Class type) {
if(List.class.isAssignableFrom(type))
{
return true;
}
return false;
}
/* (non-Javadoc)
* @see com.thoughtworks.xstream.converters.SingleValueConverter#toString(java.lang.Object)
*/
@Override
public String toString(Object obj) {
@SuppressWarnings("unchecked")
List<String> hobbies=(List<String>) obj;
StringBuffer buffer=new StringBuffer();
for(int i=0;i<hobbies.size()-1;i++)
{
buffer.append(hobbies.get(i));
buffer.append("#");
}
if(hobbies.size()>0)
{
buffer.append(hobbies.get(hobbies.size()-1));
}
return buffer.toString();
}
/* (non-Javadoc)
* @see com.thoughtworks.xstream.converters.SingleValueConverter#fromString(java.lang.String)
*/
@Override
public Object fromString(String str) {
String[] values =str.split("#");
return new ArrayList<String>(Arrays.asList(values));
}
}
同样我们可以自定义birthday属性的序列化和反序列化的方式。
xstream.registerLocalConverter(Student.class, "birthDay", new DateValueConverter()); DateValueConverter的代码如下：
public class DateValueConverter implements Converter {
@Override
public boolean canConvert(Class type) {
if (XMLGregorianCalendar.class.isAssignableFrom(type)) {
return true;
}
return false;
}
@Override
public void marshal(Object source, HierarchicalStreamWriter writer,
MarshallingContext context) {
XMLGregorianCalendar birthday = (XMLGregorianCalendar) source;
writer.setValue(birthday.toString());
}
@Override
public Object unmarshal(HierarchicalStreamReader reader,
UnmarshallingContext context) {
String value = reader.getValue();
SimpleDateFormat format = new SimpleDateFormat("yyyy-mm-dd");
try {
Date date = format.parse(value);
XMLGregorianCalendar c = DatatypeFactory.newInstance()
.newXMLGregorianCalendarDate(date.getYear(),
date.getMonth(), date.getDay(),
DatatypeConstants.FIELD_UNDEFINED);
return c;
} catch (ParseException | DatatypeConfigurationException e) {
return null;
}
}
}
我们会发现每次在序列号birthday字段的时候总是会多个一个class属性，看着很是不爽。原来是XStream在序列号的时候会判断字段的类型和实际的类型是否为同一个class。 我们可以通过设置系统别名来去除掉该属性。增加如下代码： xstream.aliasSystemAttribute(null, "class");
XStream对命名空间的支持：
并不是所有的XMLDriver都支持命名空间，StaxDriver支持命名空间，我们修改测试代码如下：
QNameMap qNameMap=new QNameMap();
qNameMap.registerMapping(new QName("http://test", "school", "test"), "school");
StaxDriver staxDriver=new StaxDriver(qNameMap);
XStream xstream = new XStream(staxDriver);
xstream.alias("school", School.class);
这样序列号出来结果如下：
<?xml version="1.0" ?><test:school xmlns:test="http://test" name="实验"><address>南京雨花台区</address><student name="张三"><address>南京市xx路</address><birthDay>2014-11-11</birthDay><hobbies>游泳#乒乓球</hobbies></student></test:school>实验
三、比较（个人意见）
1、jaxb是基于xsd的，对扩展属性和扩展元素命名空间提供了很好的支持
2、jaxb可以是基于属性（getter/setter）方法，而xstream只能支持字段。如果需要序列化的类没有字段（比如所有的东西都存入map中），jaxb可以很轻松的搞定。
3、jaxb是jdk内置的，无需引入额外的jar包