sax 解析器 returns 来自 xml 的空字符串

Question

我正在尝试用 stax 解析 xml。在我转到 xml 中的这一行之后 -

<temperature>38</temperature>

我得到一个空字符串值。为什么会这样？我能做些什么来解决这个问题？我的 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>

我的代码：

  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();
    }

和堆栈跟踪：

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

您在 startElement() 中的案例代码正在搜索 "GrowingTips" 而不是 "growingTips"，并且案例语句区分大小写。因此在 endElement() 代码中，当您尝试设置温度时，tips 为 null，并导致抛出 NullPointerException。

Answer 2

你的characters()方法是错误的：

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

文本数据可以按解析器选择的任何方式分成块，并在 characters() 的多次调用中传送。您需要附加到 content 的值，而不是每次都覆盖它。

sax 解析器 returns 来自 xml 的空字符串

sax parser returns empty string from xml

java

xml

sax

saxparser