JAXB玩轉命名空間

聲明：若是你正在發愁xml命名空間及其前綴問題，那麼請繼續，不然請跳過

本文講解使用jaxb結合dom4j的XMLFilterImpl過濾器實現序列化和反序列化的徹底控制

主要實現如下功能

• 序列化及反序列化時忽略命名空間
• 序列化時使用@XmlRootElement(namespace="http://www.lzrabbit.cn")註解做爲類的默認命名空間，完全消除命名空間前綴
• 序列化時引用類有不一樣命名空間時也不會生成命名空間前綴，而是在具體的xml節點上添加相應的xmlns聲明
• 其它的xml節點命名及命名空間需求
• 同一個包下有多個命名空間
• 自定義命名空間前綴

依賴的jar dom4j

 <dependency>
            <groupId>dom4j</groupId>
            <artifactId>dom4j</artifactId>
            <version>1.6.1</version>
 </dependency>

主要原理就是在序列化和反序列化時經過XMLFilterImpl的匿名實現類實現命名空間及xml節點名稱的控制，實現多樣化需求，廢話很少說直接上代碼，有更多個性化需求的看官請自行擴展

package cn.lzrabbit.util;

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

import javax.xml.bind.*;
import javax.xml.transform.sax.SAXSource;

import org.dom4j.io.OutputFormat;
import org.dom4j.io.XMLWriter;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.XMLFilterImpl;
import org.xml.sax.helpers.XMLReaderFactory;

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");// //編碼格式
            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頭聲明信息

            StringWriter out = new StringWriter();
            OutputFormat format = new OutputFormat();
            format.setIndent(true);
            format.setNewlines(true);
            format.setNewLineAfterDeclaration(false);
            XMLWriter writer = new XMLWriter(out, format);

            XMLFilterImpl nsfFilter = new XMLFilterImpl() {
                private boolean ignoreNamespace = false;
                private String rootNamespace = null;
                private boolean isRootElement = true;

                @Override
                public void startDocument() throws SAXException {
                    super.startDocument();
                }

                @Override
                public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
                    if (this.ignoreNamespace) uri = "";
                    if (this.isRootElement) this.isRootElement = false;
                    else if (!uri.equals("") && !localName.contains("xmlns")) localName = localName + " xmlns=\"" + uri + "\"";

                    super.startElement(uri, localName, localName, atts);
                }

                @Override
                public void endElement(String uri, String localName, String qName) throws SAXException {
                    if (this.ignoreNamespace) uri = "";
                    super.endElement(uri, localName, localName);
                }

                @Override
                public void startPrefixMapping(String prefix, String url) throws SAXException {
                    if (this.rootNamespace != null) url = this.rootNamespace;
                    if (!this.ignoreNamespace) super.startPrefixMapping("", url);

                }
            };
            nsfFilter.setContentHandler(writer);
            marshaller.marshal(obj, nsfFilter);
            return out.toString();

        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    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));
            SerializeUtil obj = new SerializeUtil();
            XMLReader reader = XMLReaderFactory.createXMLReader();
            XMLFilterImpl nsfFilter = new XMLFilterImpl() {
                private boolean ignoreNamespace = false;

                @Override
                public void startDocument() throws SAXException {
                    super.startDocument();
                }

                @Override
                public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
                    if (this.ignoreNamespace) uri = "";
                    super.startElement(uri, localName, qName, atts);
                }

                @Override
                public void endElement(String uri, String localName, String qName) throws SAXException {
                    if (this.ignoreNamespace) uri = "";
                    super.endElement(uri, localName, localName);
                }

                @Override
                public void startPrefixMapping(String prefix, String url) throws SAXException {
                    if (!this.ignoreNamespace) super.startPrefixMapping("", url);
                }
            };
            nsfFilter.setParent(reader);
            InputSource input = new InputSource(new StringReader(xml));
            SAXSource source = new SAXSource(nsfFilter, input);
            return (T) unmarshaller.unmarshal(source);
        } catch (Exception e) {
            throw new RuntimeException(e.getMessage());
        }
    }
}

View Code

示例實體類

import javax.xml.bind.annotation.*;

@XmlRootElement(namespace="http://www.lzrabbit.cn/")
@XmlAccessorType(XmlAccessType.FIELD)
public class ClassA {
    private int classAId;
    
    @XmlElement(name="ClassAName")
    private String classAName;

    @XmlElement(namespace="http://www.cnblogs.com/")
    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;
    }
}

import javax.xml.bind.annotation.*;

@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;
    }
}

View Code

調用

import cn.lzrabbit.util.XmlUtil;

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));
    }

}

輸出結果：

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

能夠看到輸出的xml徹底達到咱們的預期

實現細節都在代碼裏面了，很簡單，當遇到有特殊需求的xml命名空間問題時，不再用愁了