JAXB玩转命名空间

声明：如果你正在发愁xml命名空间及其前缀问题，那么请继续，否则请跳过

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

 <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

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");// //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());
        }
    }
}

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