JAXB命名空间及前缀_动力节点Java学院整理

时间:2022-04-21 02:42:00

本文讲解使用jaxb结合dom4j的XMLFilterImpl过滤器实现序列化和反序列化的完全控制

主要实现以下功能

  • 序列化及反序列化时忽略命名空间
  • 序列化时使用@XmlRootElement(namespace="http://www.lzrabbit.cn")注解作为类的默认命名空间,彻底消除命名空间前缀
  • 序列化时引用类有不同命名空间时也不会生成命名空间前缀,而是在具体的xml节点上添加相应的xmlns声明
  • 其它的xml节点命名及命名空间需求
  • 同一个包下有多个命名空间
  • 自定义命名空间前缀

依赖的jar dom4j

 
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<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时通过XMLFilterImpl的匿名实现类实现命名空间及xml节点名称的控制,实现多样化需求,废话不多说直接上代码,有更多个性化需求的看官请自行扩展

 
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package com.bjpowernode.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");// //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 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());
  }
 }
}

示例实体类

 
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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;
 }
}

调用

 
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import com.bjpowernode.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));
 }
 
}

输出结果:

 
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<?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>

可以看到输出的xml完全达到我们的预期

实现细节都在代码里面了,很简单,当遇到有特殊需求的xml命名空间问题时,再也不用愁了

总结

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