Java与XML的故事二：XML与Java Object互相转换

XML文件和Java对象转换是一件非常简单的事情，有了annotation的java文件和XML schema XSD文件，可以简单的通过JAXB API来实现XML与Java Object转换

marshaller Java to XML

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prviate static javax.xml.bind.JAXBContext jaxbCtx = null;private static Schema schema = null;static {jaxbCtx = javax.xml.bind.JAXBContext.newInstance(T.class); //jaxbcontext is thread safeSchemaFactory sf = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI); // factory not thread safe        Schema schema = sf.newSchema(new File("T.xsd")); //schema is thread safe}private static void validate(T t){        JAXBSource source = new JAXBSource(jaxbCtx, t);        Validator validator = schema.newValidator();       // validator.setErrorHandler(new MyValidationErrorHandler());        validator.validate(source); // SAXException throws if failed, you can define your error handler or just notify the exception to caller}public static void marshToFile(T t, File file){    validate(t);            javax.xml.bind.Marshaller marshaller = jaxbCtx.createMarshaller(); // not thread safe            marshaller.setProperty(javax.xml.bind.Marshaller.JAXB_ENCODING, "UTF-8");             marshaller.setProperty(javax.xml.bind.Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);         //   if(logger.isDebugEnabled){ StringWriter sw = new StringWriter(); marshaller.marshal(t, sw); logger.debug(sw.toString());}            marshaller.marshal( t, file);}

unmarshaller XML to Java

public static T unmarshFromXml(File xmlFile){        Unmarshaller unmarshaller = jaxbCtx.createUnmarshaller();        unmarshaller.setSchema(schema);        //unmarshaller.setEventHandler(new MyValidationErrorHandler());        T test = (T) unmarshaller.unmarshal(xmlFile); //UnmarshalException if failed        }

ErrorHandler

默认抛出SAXException如果在validation的时候出现问题(fatal error)，可以自己定制handler实现出现错误时候系统行为，例如更细节的错误记录。

public class MyValidationErrorHandler implements ErrorHandler {......    public void warning(SAXParseException ex) {        logger.error(ex.getMessage());    }    public void error(SAXParseException ex) {        logger.error(ex.getMessage());    }    public void fatalError(SAXParseException ex) throws SAXException {        throw ex;    }}