sax解析器从xml返回空字符串

Question

i'm trying to parse xml with stax. after i'm going to this line in xml -

<temperature>38</temperature>

i am get a empty string value. Why this happens ? What can i do to solve this ? my xml :

<?xml version="1.0" encoding="UTF-8"?>
<flowers>
    <flower name="rose">
        <soil>podzolic</soil>   
        <visualParameters>
            <stemColor>Green</stemColor>
            <leafColor>Red</leafColor>
            <averageSize>50</averageSize>
        </visualParameters>
        <growingTips>
            <temperature>38</temperature>
            <watering>1200</watering>
            <value>photophilous</value>
        </growingTips>
    <multiplying>bySeeds</multiplying>
    <origin>Belarus</origin>
        <description>Classic Choice</description>
    </flower>
</flowers>

my code :

  List<Flower> getFlowerList() {
        return flowerList;
    }
    public void startElement(String namespaceURI, String localName, String qName, Attributes attrs) throws SAXException { 
        switch (qName) {
            case "flowers":
                flowerList = new ArrayList<Flower>();
                break;
            case "flower":
                flower = new Flower();
                flower.setName(attrs.getValue("name"));
                break;
            case "visualParameters":
                visual = new VisualParameters();
                break;
            case "GrowingTips":
                tips = new GrowingTips();
                break;
        }

    }
    public void endElement(String namespaceURI, String localName, String qName) throws SAXException { 
        switch (qName) {
            case "flower":
                flowerList.add(flower);
                break;
            case "soilType":
                soil = new SoilType();
                soil.setValue(SoilName.fromValue(content));
                break;
            case "origin":
                flower = new Flower();
                flower.setOrigin(content);
              break;
            case "averageSize":
                  visual.setAverageSize(Integer.valueOf(content));
              flower.setParameters(visual);
               break;
            case "leafColor":
                visual.setLeafColor(content);
                flower.setParameters(visual);
                break;
            case "temperature":
             //in this line content = ""
                tips.setTemperature(Integer.valueOf(content));

                break;
            case "stemColor":
                visual.setStemColor(content);
                flower.setParameters(visual);
                break;
            case "watering":
                tips.setWatering(Integer.valueOf(content));
                break;
            case "lightingType":
                tips.setValue(LightingName.fromValue(content));
                break;
            case "multiplying":
                multiplyingType = new MultiplyingType();
                multiplyingType.setValue(MultiplyingName.fromValue(content));
                break;
            case "description":
                flower.setDescription(content);
                break;
        }

    }
 public void characters(char[] ch, int start, int length) {
        content = String.copyValueOf(ch, start, length).trim();
    }

and the stacktrace:

java.lang.NullPointerException
    at tasks.five.parser.SAXHandler.endElement(SAXHandler.java:75)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl.parse(Unknown Source)
    at javax.xml.parsers.SAXParser.parse(Unknown Source)
    at tasks.five.parser.SAXParserClass.SAXParser(SAXParserClass.java:22)
    at tasks.five.command.SAXParserCommand.execute(SAXParserCommand.java:13)
    at tasks.five.command.CommandExecutor.execute(CommandExecutor.java:21)
    at tasks.five.runner.Main.main(Main.java:14)

Answer 1

Your case code in startElement() is searching for "GrowingTips" instead of "growingTips" , and case statements are case sensitive. So in the endElement() code, when you try to set the temperature, tips is null, and causes NullPointerException to be thrown.

Answer 2

Your characters() method is wrong:

content = String.copyValueOf(ch, start, length).trim();

Text data can be divided up into chunks any way the parser chooses, and delivered in multiple calls of characters() . You need to append to the value of content , not to overwrite it each time.