JAXB最佳实践

JAXB主要用来实现对象和XML之间的序列化和反序列化。

本文主要总结JAXB基本使用方法和注意事项！

通过下文的XML示例内容进行JAXB的简单实践 

<?xml version="1.0" encoding="UTF-8"?>
<Provinces>
    <Province id="B001">
        <name>北京</name>
        <code>30000</code>
    </Province>
    <Province id="Z001">
        <name>浙江</name>
        <code>60000</code>
    </Province>
    <Province id="J001">
        <name>江苏</name>
        <code>90000</code>
        <city citycode="90001">南京市</city>
        <city citycode="90002">盐城市</city>
        <city citycode="90003">扬州市</city>
        <city citycode="90004">南通市</city>
    </Province>
</Provinces>

JavaBean to XML

一、分析citys.xml，可以定义三个示例类ProvincesBean,ProvinceBean,CityBean.java

package my.jaxb.bean;

import java.util.List;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

/**
    <Provinces>
        <Province id="B001">...
        <Province id="B002">...
        <Province id="J001">...
    </Provinces>
**/
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "Provinces")
public class ProvincesBean
{
    @XmlElement(name = "Province")
    private List<ProvinceBean> provinces = null;
    
    public List<ProvinceBean> getProvinces()
    {
        return provinces;
    }
    
    public void setProvinces(List<ProvinceBean> provinces)
    {
        this.provinces = provinces;
    }
    
    public String toString()
    {
        return "ProvincesBean ( provinces = " + this.provinces + " )";
    }
}

package my.jaxb.bean;

import java.util.List;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

/**
    <Province id="J001">
        <name>江苏</name>
        <code>90000</code>
        <city citycode="90001">南京市</city>
        <city citycode="90002">盐城市</city>
        <city citycode="90003">扬州市</city>
        <city citycode="90004">南通市</city>
    </Province>
 **/
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "Province")
public class ProvinceBean
{
    @XmlAttribute
    private String id = "";
    
    private String name = "";
    
    private String code = "";
    
    @XmlElement(name = "city")
    private List<CityBean> citys = null;
    
    public String getId()
    {
        return id;
    }
    
    public void setId(String id)
    {
        this.id = id;
    }
    
    public String getName()
    {
        return name;
    }
    
    public void setName(String name)
    {
        this.name = name;
    }
    
    public List<CityBean> getCitys()
    {
        return citys;
    }
    
    public void setCitys(List<CityBean> citys)
    {
        this.citys = citys;
    }
    
    public String getCode()
    {
        return code;
    }
    
    public void setCode(String code)
    {
        this.code = code;
    }
    
    public String toString()
    {
        return "ProvinceBean ( id = " + this.id + " name = " + this.name + " code = " + this.code + " citys = "
                + this.citys + " )";
    }
}

package my.jaxb.bean;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlValue;

/**
    <city citycode="90001">南京市</city>
**/
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "city")
public class CityBean
{
    public CityBean()
    {
    }
    
    public CityBean(String cityCode, String value)
    {
        super();
        this.cityCode = cityCode;
        this.value = value;
    }
    
    @XmlAttribute(name = "citycode")
    private String cityCode = "";
    
    @XmlValue
    private String value = "";
    
    public String getCityCode()
    {
        return cityCode;
    }
    
    public void setCityCode(String cityCode)
    {
        this.cityCode = cityCode;
    }
    
    public String getValue()
    {
        return value;
    }
    
    public void setValue(String value)
    {
        this.value = value;
    }
    
    public String toString()
    {
        return "CityBean ( cityCode = " + this.cityCode + " value = " + this.value + " )";
    }
}

二、编写序列化和反序列化的工具类-XmlUtils 

package my.jaxb.comm;

import java.io.File;
import java.io.StringReader;
import java.io.StringWriter;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class XmlUtils
{
    // JavaBean to XML
    public static String toXML(Object obj)
    {
        try
        {
            JAXBContext context = JAXBContext.newInstance(obj.getClass());
            
            Marshaller marshaller = context.createMarshaller();
            // 设置编码格式
            marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
            // 是否格式化生成的XML
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
            // 是否省略XML头声明信息
            marshaller.setProperty(Marshaller.JAXB_FRAGMENT, false);
            
            StringWriter writer = new StringWriter();
            
            marshaller.marshal(obj, writer);
            
            return writer.toString();
        }
        catch (JAXBException e)
        {
            throw new RuntimeException(e.getMessage());
        }
    }
    
    // XML to JavaBean
    public static <MY> MY fromXML(String xml, Class<MY> declareType)
    {
        try
        {
            JAXBContext context = JAXBContext.newInstance(declareType);
            
            Unmarshaller unmarshaller = context.createUnmarshaller();
            
            Object obj = unmarshaller.unmarshal(new StringReader(xml));
            
            return (MY) obj;
        }
        catch (JAXBException e)
        {
            throw new RuntimeException(e.getMessage());
        }
    }
    
    // XML(path) to JavaBean
    public static <MY> MY fromXMLPath(String xmlPath, Class<MY> declareType)
    {
        try
        {
            JAXBContext context = JAXBContext.newInstance(declareType);
            
            Unmarshaller unmarshaller = context.createUnmarshaller();
            
            Object obj = unmarshaller.unmarshal(new File(xmlPath));
            
            return (MY) obj;
        }
        catch (JAXBException e)
        {
            throw new RuntimeException(e.getMessage());
        }
    }
    
}

 三、编写测试代码，内部实现了JavaBean to XML和XML to JavaBean两个操作

package my.jaxb.test;

import java.util.ArrayList;
import java.util.List;

import my.jaxb.bean.CityBean;
import my.jaxb.bean.ProvinceBean;
import my.jaxb.bean.ProvincesBean;
import my.jaxb.comm.XmlUtils;

public class ToXMLFoo
{
    public static void main(String[] args)
    {
        ProvincesBean provinces = new ProvincesBean();
        provinces.setProvinces(getProvinces());
        
        // JavaBean to XML
        String xml = XmlUtils.toXML(provinces);
        
        System.out.println(xml);
        
        System.out.println("------------------------------");
        
        // XML to JavaBean
        provinces = XmlUtils.fromXML(xml, ProvincesBean.class);
        
        System.out.println(provinces);
    }
    
    private static List<ProvinceBean> getProvinces()
    {
        List<ProvinceBean> provList = new ArrayList<ProvinceBean>();
        
        ProvinceBean prov = new ProvinceBean();
        prov.setId("B001");
        prov.setName("北京");
        prov.setCode("30000");
        
        ProvinceBean prov2 = new ProvinceBean();
        prov2.setId("Z001");
        prov2.setName("浙江");
        prov2.setCode("60000");
        
        ProvinceBean prov3 = new ProvinceBean();
        prov3.setId("J001");
        prov3.setName("江苏");
        prov3.setCode("90000");
        
        // 单独增加城市
        prov3.setCitys(getCitys());
        
        provList.add(prov);
        provList.add(prov2);
        provList.add(prov3);
        
        return provList;
    }
    
    private static List<CityBean> getCitys()
    {
        List<CityBean> cityList = new ArrayList<CityBean>();
        
        CityBean city = new CityBean("90001", "南京市");
        CityBean city2 = new CityBean("90002", "盐城市");
        CityBean city3 = new CityBean("90003", "扬州市");
        CityBean city4 = new CityBean("90004", "南通市");
        cityList.add(city);
        cityList.add(city2);
        cityList.add(city3);
        cityList.add(city4);
        
        return cityList;
    }
}

四、测试输出结果 

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Provinces>
    <Province id="B001">
        <name>北京</name>
        <code>30000</code>
    </Province>
    <Province id="Z001">
        <name>浙江</name>
        <code>60000</code>
    </Province>
    <Province id="J001">
        <name>江苏</name>
        <code>90000</code>
        <city citycode="90001">南京市</city>
        <city citycode="90002">盐城市</city>
        <city citycode="90003">扬州市</city>
        <city citycode="90004">南通市</city>
    </Province>
</Provinces>

------------------------------
ProvincesBean ( provinces = [ProvinceBean ( id = B001 name = 北京 code = 30000 citys = null ), ProvinceBean ( id = Z001 name = 浙江 code = 60000 citys = null ), ProvinceBean ( id = J001 name = 江苏 code = 90000 citys = [CityBean ( cityCode = 90001 value = 南京市 ), CityBean ( cityCode = 90002 value = 盐城市 ), CityBean ( cityCode = 90003 value = 扬州市 ), CityBean ( cityCode = 90004 value = 南通市 )] )] )

   

XML to JavaBean

一、直接编写测试代码，内部实现了XML to JavaBean的操作 

package my.jaxb.test;

import my.jaxb.bean.ProvincesBean;
import my.jaxb.comm.XmlUtils;

public class FromXMLFoo
{
    public static void main(String[] args)
    {
        String xmlPath = FromXMLFoo.class.getResource("/").getPath() + "citys.xml";
        
        // XML(path) to JavaBean
        ProvincesBean bean = XmlUtils.fromXMLPath(xmlPath, ProvincesBean.class);
        
        System.out.println(bean);
    }
    
}

二、测试输出结果

ProvincesBean ( provinces = [ProvinceBean ( id = B001 name = 北京 code = 30000 citys = null ), ProvinceBean ( id = Z001 name = 浙江 code = 60000 citys = null ), ProvinceBean ( id = J001 name = 江苏 code = 90000 citys = [CityBean ( cityCode = 90001 value = 南京市 ), CityBean ( cityCode = 90002 value = 盐城市 ), CityBean ( cityCode = 90003 value = 扬州市 ), CityBean ( cityCode = 90004 value = 南通市 )] )] )

注意事项

1、要序列化的类加上@XmlRootElement注解，否则会报错！

2、JAXB序列化XML时 默认序列化getter和setter，且getter和setter必须成对出现才会被序列化。

3、属性名称，默认序列化出来的类和属性名称默认是首字母转换为小写，若需要控制属性名称需要在getter或setter上
    使用 @XmlElement(name = "Province") 指定名称，此处要注意的是@XmlElement也可以放置在getter或setter上都行，
    但只能放一个，也就是说不能同时在getter和setter或field字段三者中间任意二者上同时使用 @XmlElement注解！

4、如控制根节点名称？
Re: 使用@XmlRootElement指定name属性即可，如@XmlRootElement(name = "Provinces")。

5、怎么添加命名空间
Re: 使用@XmlRootElement(namespace="my.jaxb") 指定namespace属性，此处不做代码示例。

6、怎么精确控制每个属性名称
Re: JAXB自动转化为首字母小写会导致不可预料的属性名称出现,不嫌麻烦的话为每个属性设置@XmlElement(name=""),想省事的话使用Field字段名称即可。

7、怎么样实现序列化时使用Field字段而不是使用setter和getter
Re: 在要使用的类上面加上@XmlAccessorType(XmlAccessType.FIELD)注解，并指定为XmlAccessType.FIELD,
    这里强烈推荐使用@XmlAccessorType(XmlAccessType.FIELD)注解，因为这样你可以精确的控制每个元素的名称,
    而不需要为每个属性去设置@XmlElement(name="")注解，当然也可以在Field上使用@XmlElement注解。

8、一个元素既有属性也有文本内容情况如何配置？
Re: 如：<city citycode="90001">南京市</city> ，此时citycode字段通过@XmlAttribute(name = "citycode")控制，value字段通过@XmlValue控制即可。