浅谈JAXB规范化标准

在公司的项目中发现了Marshaller和Unmarshaller的使用，于是开始了对这两个类的探索，最终追根溯源，到了JAXB标准，到底什么是JAXB标准呢？

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。

注意事项：

1.要序列化的类上加@XmlRootElement，否则会报错：

2.JAXB将对象序列化成XML时，xml节点和类的属性一一对应，其原理是根据类属性的setter和getter方法来序列化的，且必须两者成对出现，类似于Spring的依赖注入时，也需要setter方法存在方可注入，却别在于前者必须成对出现。

3.序列化出的节点名称。默认序列化出来的XML节点是类的属性首字母小写，如果想要改变XML节点的值，可以再某个属性的setter或者getter方法上加上@XmlElement(name = "XXX")，值得注意的是，不管是加在setter上，还是加在getter上，只需要加一个即可，两个都加会报错。

4.控制根节点的名称。同理如上，在@XmlRootElement标签里加上name属性即可。

5.命名空间的添加。在@XmlRootElement标签里加上namespace属性，如果既加name，又加namespace，中间用逗号隔开。

6.要序列化的类必须含有无参构造器，否则报错。

话不多说，直接上代码：

Factory类

package com;

import javax.xml.bind.annotation.XmlElement;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name = "FactoryTest", namespace = "fuqinqin")

public class Factory {

private String name;

private String address;

private Worker worker;

public Factory(){}

public Factory(String name, String address, Worker worker) {

super();

this.name = name;

this.address = address;

this.worker = worker;

}

@XmlElement(name = "factoryName")

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

public Worker getWorker() {

return worker;

}

public void setWorker(Worker worker) {

this.worker = worker;

}

@Override

public String toString() {

return "Factory [name=" + name + ", address=" + address + ", worker="

+ worker + "]";

}

}

Worker类：

package com;

public class Worker {

private String name;

private String address;

private String no;

public Worker(){}

public Worker(String name, String address, String no) {

super();

this.name = name;

this.address = address;

this.no = no;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

public String getNo() {

return no;

}

public void setNo(String no) {

this.no = no;

}

@Override

public String toString() {

return "Worker [name=" + name + ", address=" + address + ", no=" + no

+ "]";

}

}

测试类：

package com;

import java.io.StringReader;

import java.io.UnsupportedEncodingException;

import javax.xml.bind.JAXBContext;

import javax.xml.bind.JAXBException;

import javax.xml.bind.Marshaller;

import javax.xml.bind.Unmarshaller;

import org.junit.Test;

public class MainTest {

@Test

public void beanToXML() throws JAXBException, UnsupportedEncodingException{

Worker worker = new Worker("wangda", "shanghai", "00101");

Factory factory = new Factory("上海机械厂", "浦东新区张江高科", worker);

JAXBContext context = JAXBContext.newInstance(Factory.class);

Marshaller marshaller = context.createMarshaller();

//乱码转换

marshaller.setProperty(Marshaller.JAXB_ENCODING, "GBK");

//格式化生成的xml串

marshaller.setProperty("jaxb.formatted.output", true);

//是否省略XML头申明信息

marshaller.setProperty(Marshaller.JAXB_FRAGMENT, false);

marshaller.marshal(factory, System.out);

}

@Test

public void XMLToBean() throws JAXBException{

String xmlStr = "<?xml version=\"1.0\" encoding=\"GBK\" standalone=\"yes\"?><ns2:FactoryTest xmlns:ns2=\"fuqinqin\"><address>浦东新区张江高科</address><factoryName>上海机械厂</factoryName><worker><address>shanghai</address><name>wangda</name><no>00101</no></worker></ns2:FactoryTest>";

JAXBContext context = JAXBContext.newInstance(Factory.class);

Unmarshaller unmarshaller = context.createUnmarshaller();

Factory factory = (Factory) unmarshaller.unmarshal(new StringReader(xmlStr));

System.out.println("factory : "+factory);

}

}

输出结果是：

factory : Factory [name=上海机械厂, address=浦东新区张江高科, worker=Worker [name=wangda, address=shanghai, no=00101]]

<?xml version="1.0" encoding="GBK" standalone="yes"?>

<ns2:FactoryTest xmlns:ns2="fuqinqin">

<address>浦东新区张江高科</address>

<factoryName>上海机械厂</factoryName>

<worker>

<address>shanghai</address>

<name>wangda</name>

<no>00101</no>

</worker>

</ns2:FactoryTest>

这里要介绍介个常用的JAXB属性设置：

1. marshaller.setProperty(Marshaller.JAXB_ENCODING, "GBK"); 设置序列化出来的xml文件的编码格式，可以有效的处理乱码问题

2.marshaller.setProperty("jaxb.formatted.output", true); 值若为true，则生成的xml会带有换行，且有缩进

3.marshaller.setProperty(Marshaller.JAXB_FRAGMENT, false); 值若为true，则生成的xml的头信息会被省略