java使用jaxb操作xml示例

首先定义两个示例类ClassA,ClassB,用于后续的示例演示

package cn.lzrabbit;
public class ClassA {
    private int classAId;
    private String classAName;
    private ClassB classB;
    public int getClassAId() {
        return classAId;
    }
    public void setClassAId(int classAId) {
        this.classAId = classAId;
    }
    public String getClassAName() {
        return classAName;
    }
    public void setClassAName(String classAName) {
        this.classAName = classAName;
    }
    public ClassB getClassB() {
        return classB;
    }
    public void setClassB(ClassB classB) {
        this.classB = classB;
    }
}
ClassA
package cn.lzrabbit;
public class ClassB {
    private int classBId;
    private String classBName;
    public int getClassBId() {
        return classBId;
    }
    public void setClassBId(int classBId) {
        this.classBId = classBId;
    }
    public String getClassBName() {
        return classBName;
    }
    public void setClassBName(String classBName) {
        this.classBName = classBName;
    }
}
ClassB

用于序列化的XmlUtil

package cn.lzrabbit;
import java.io.StringReader;
import java.io.StringWriter;
import javax.xml.bind.*;
public class XmlUtil {
    public static String toXML(Object obj) {
        try {
            JAXBContext context = JAXBContext.newInstance(obj.getClass());
            Marshaller marshaller = context.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");// //编码格式
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);// 是否格式化生成的xml串
            marshaller.setProperty(Marshaller.JAXB_FRAGMENT, false);// 是否省略xm头声明信息
            StringWriter writer = new StringWriter();
            marshaller.marshal(obj, writer);
            return writer.toString();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
    @SuppressWarnings("unchecked")
    public static <T> T fromXML(String xml, Class<T> valueType) {
        try {
            JAXBContext context = JAXBContext.newInstance(valueType);
            Unmarshaller unmarshaller = context.createUnmarshaller();
            return (T) unmarshaller.unmarshal(new StringReader(xml));
        } catch (Exception e) {
            throw new RuntimeException(e.getMessage());
        }
    }
}
XmlUtil

调用如下:

package cn.lzrabbit;

public class MainRun {
    /**
     * @param args
     */
    public static void main(String[] args) {
        ClassB classB = new ClassB();
        classB.setClassBId(22);
        classB.setClassBName("B2");
        ClassA classA = new ClassA();
        classA.setClassAId(11);
        classA.setClassAName("A1");
        classA.setClassB(classB);
        System.out.println(XmlUtil.toXML(classA));
    }
}
MainRun

输出结果如下:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<classA>
    <classAId>11</classAId>
    <classAName>A1</classAName>
    <classB>
        <classBId>22</classBId>
        <classBName>B2</classBName>
    </classB>
</classA>

这里要注意以下几点

1要序列化的类加上 @XmlRootElement注解,否则会报错(错误提示很清晰,这里就不贴出来了)

2JAXB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="ClassAId") 指定名称,这里要注意的是@XmlElement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上使用@XmlElement注解

4如何控制根节点名称?
使用@XmlRootElement指定name属性即可,如@XmlRootElement(name="ClassA")

5怎么添加命名空间
使用@XmlRootElement(namespace="cn.lzrabbit") 指定namespace属性

6怎么精确控制每个属性名称
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

7怎么样实现序列化时使用Field字段而不是使用setter和getter
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

下面给出使用了使用如上注解后的代码示例

@XmlRootElement(namespace="cn.lzrabbit")
@XmlAccessorType(XmlAccessType.FIELD)
public class ClassA {
    private int classAId;
    
    @XmlElement(name="ClassAName")
    private String classAName;
    private ClassB classB;
    public int getClassAId() {
        return classAId;
    }
    public void setClassAId(int classAId) {
        this.classAId = classAId;
    }
    public String getClassAName() {
        return classAName;
    }
    public void setClassAName(String classAName) {
        this.classAName = classAName;
    }
    public ClassB getClassB() {
        return classB;
    }
    public void setClassB(ClassB classB) {
        this.classB = classB;
    }
}
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class ClassB {
    private int ClassBId;
    private String ClassBName;
    public int getClassBId() {
        return ClassBId;
    }
    public void setClassBId(int classBId) {
        this.ClassBId = classBId;
    }
    public String getClassBName() {
        return ClassBName;
    }
    public void setClassBName(String classBName) {
        this.ClassBName = classBName;
    }
}

输出xml为

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:classA xmlns:ns2="cn.lzrabbit">
    <classAId>11</classAId>
    <ClassAName>A1</ClassAName>
    <classB>
        <ClassBId>22</ClassBId>
        <ClassBName>B2</ClassBName>
    </classB>
</ns2:classA>

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