使用哪种设计模式来改进此Java程序

我编写了一个程序来解析XML文件,以获取一个名为SerialNum的特定标记值,该值包含在Header标记中.该文件构造如下:

它包含1个标题和1个正文

Header可能包含许多SerialNum标记.我们需要提取最后一个标签的值.

我使用Stax解析器来获取SerialNum值,我编写了这段代码:

public String findIdValue(HttpServletRequest request) {

    String serialNumberValue = null;

    if(request != null){
        ServletInputStream servletInstream;
        try {
            servletInstream = request.getInputStream();
            XMLInputFactory factory = XMLInputFactory.newInstance();
            XMLStreamReader xmlStreamReader = factory.createXMLStreamReader(servletInstream);
            //begin parsing if we get 

            //end parsing if we get 
 or 

            int event = xmlStreamReader.getEventType();
            boolean enableToParse = false;
            boolean gotSerialNumber = false;
            boolean parseComplete = false;

            while( (xmlStreamReader.hasNext()) && (!parseComplete) ){
                switch(event) {
                case XMLStreamConstants.START_ELEMENT:
                    if("Header".equals(xmlStreamReader.getLocalName())){
                        //tag is header, so begin parse
                        enableToParse = true;
                    }else if(("SerialNum".equals(xmlStreamReader.getLocalName())) && (enableToParse) ){
                        //tag is serialNum so enable to save the value of serial number
                        gotSerialNumber = true;
                    }
                    break;
                case XMLStreamConstants.CHARACTERS:
                    //get serial number and end the parsing
                    if(gotSerialNumber){
                        //get wsa and end the parsing
                        serialNumberValue = xmlStreamReader.getText();
                        gotSerialNumber = false;                            
                    }

                    break;
                case XMLStreamConstants.END_ELEMENT:
                    //when we get 
 end the parse
                    //when we get  reinit flags
                    //when we get  end the parse even we don't get a serial number
                    if("Header".equals(xmlStreamReader.getLocalName())){
                        parseComplete= true;
                    }else if("SerialNum".equals(xmlStreamReader.getLocalName())){
                        //reinit flag when we get  tag
                        gotSerialNumber = false;
                    }
                    break;
                default:
                    break;
                }
                event = xmlStreamReader.next();
            }


        } catch (final XMLStreamException e) {
            //catch block
            LOG.info("Got an XMLStreamException exception. " + e.getMessage());
        }
        catch (final IOException e1) {
            //catch block
            LOG.info("Got an IOException exception. " + e1.getMessage());
        }

    }


    return serialNumberValue;
}

此代码提取所需的值但代码质量不是很好:它不易于阅读和维护.它包含一个switch case和if else块嵌套在while循环中.使用哪种设计模式来提高代码质量？