为什么在运行 StAX Parser 时会出现 NullPointerException? [英] Why I get NullPointerException when running StAX Parser?

问题描述

我正在尝试用 Java 编写 StAX XML 解析器，但总是出现 NullPointerException 错误.请帮我解决这个问题.完整的问题:

<块引用>

线程main"中的异常java.lang.NullPointerException 在org.example.shoesshop.parser.STAXParser.parseXMLfile(STAXParser.java:68)在 org.example.shoesshop.parser.STAXParser.main(STAXParser.java:101)

这是 StAX 解析器的类:

public class STAXParser extends DefaultHandler {私有静态列表<鞋子>parseXMLfile(字符串文件名){列表<鞋子>shoesList = new ArrayList<>();鞋子鞋子=空；XMLInputFactory xmlInputFactory = XMLInputFactory.newInstance();尝试 {XMLEventReader reader = xmlInputFactory.createXMLEventReader(new FileInputStream(fileName));而 (reader.hasNext()){XMLEvent xmlEvent = reader.nextEvent();如果(xmlEvent.isStartElement()){StartElement startElement = xmlEvent.asStartElement();if(startElement.getName().getLocalPart().equals(鞋子")){鞋子 = 新鞋子()；属性 idAttr = startElement.getAttributeByName(new QName(id"));if(idAttr != null){shoes.setId(Integer.parseInt(idAttr.getValue()));}} else if (startElement.getName().getLocalPart().equals(title")){xmlEvent = reader.nextEvent();shoes.setTitle(xmlEvent.asCharacters().getData());//错误行 68} else if (startElement.getName().getLocalPart().equals(brand")){xmlEvent = reader.nextEvent();shoes.setBrand(Brand.fromValue(xmlEvent.asCharacters().getData()));} else if (startElement.getName().getLocalPart().equals(category")){xmlEvent = reader.nextEvent();shoes.setCategory(Category.fromValue(xmlEvent.asCharacters().getData()));} else if (startElement.getName().getLocalPart().equals(season")){xmlEvent = reader.nextEvent();shoes.setSeason(Season.fromValue(xmlEvent.asCharacters().getData()));} else if (startElement.getName().getLocalPart().equals(price")){xmlEvent = reader.nextEvent();shoes.setPrice(Double.parseDouble(xmlEvent.asCharacters().getData()));}}如果(xmlEvent.isEndElement()){EndElement endElement = xmlEvent.asEndElement();if(endElement.getName().getLocalPart().equals(鞋子")){shoesList.add(shoes);}}}} catch (FileNotFoundException | XMLStreamException exc) {exc.printStackTrace();} return shoesList;}public static void main(String[] args) 抛出异常 {System.out.println(STAX 解析器");System.out.println();System.out.println("结果:\n");System.out.println();String fileName = "ShoesShop.xml";列表<鞋子>shoesList = parseXMLfile(fileName);//错误行101对于(鞋履:shoesList){System.out.println(shoes.toString());}}}

这是一个 XML 文件

<?xml-stylesheet type = "text/xsl";href = "ShoesShop.xsl"?><ss:ShoesShop xmlns:ss="http://www.example.org/ShoesShop";xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation=http://www.example.org/ShoesShop ShoesShop.xsd"><ss:shoes id="1";股票=真"><ss:title>Baltrum</ss:title><ss:brand>Gucci</ss:brand><ss:category>靴子</ss:category><ss:season>秋天</ss:season><ss:male>male</ss:male></ss:性别><ss:详细信息><ss:highlights>突出显示文本 1</ss:highlights><ss:composition>作文文本1</ss:composition></ss:详细信息><ss:price>734.0</ss:price></ss:鞋子><ss:shoes id="2";股票=真"mostWanted =真"><ss:title>阿马尔菲</ss:title><ss:brand>Dior</ss:brand><ss:category>骡子</ss:category><ss:season>冬天</ss:season><ss:female>female</ss:female></ss:性别><ss:详细信息><ss:highlights>突出显示文本 2</ss:highlights><ss:composition>作文文本2</ss:composition></ss:详细信息><ss:price>364.0</ss:price></ss:鞋子><ss:shoes id="3";股票=真"mostWanted =真"><ss:title>Korfu</ss:title><ss:brand>Mary Katrantzou</ss:brand><ss:category>运动鞋</ss:category><ss:season>春天</ss:season><ss:female>female</ss:female></ss:性别><ss:详细信息><ss:highlights>突出显示文本 3</ss:highlights><ss:composition>作文文本3</ss:composition></ss:详细信息><ss:price>173.0</ss:price></ss:鞋子></ss:鞋店>

还有一个用于鞋类的 Java 类

@XmlAccessorType(XmlAccessType.FIELD)@XmlType(name = "Shoes", propOrder = {标题"，品牌"，类别"，季节"，性别"，细节"，价格"})公开课鞋扩展实体{@XmlElement(required = true)受保护的字符串标题；@XmlElement(required = true)@XmlSchemaType(name = "string")受保护的品牌品牌；@XmlElement(required = true)@XmlSchemaType(name = "string")受保护的类别；@XmlElement(required = true)@XmlSchemaType(name = "string")受保护的季节；@XmlElement(required = true)受保护的鞋子.性别性别；@XmlElement(required = true)受保护的鞋子.详细信息；受保护的双价；@XmlAttribute(name = "stock", required = true)受保护的布尔股票；@XmlAttribute(name = "mostWanted")受保护的布尔值最想要的；公共字符串 getTitle() {返回标题；}公共无效设置标题(字符串值){this.title = 值；}公共品牌 getBrand(){回归品牌；}公共无效setBrand(品牌价值){this.brand = 价值；}公共类别 getCategory(){退货类别；}public void setCategory(Category value){this.category = 值；}公共季节 getSeason(){回归季节；}public void setSeason(季节值){this.season = 价值；}public Shoes.Gender getGender() {回归性别；}public void setGender(Shoes.Gender value) {this.gender = 值；}public Shoes.Details getDetails() {退货详情；}public void setDetails(Shoes.Details value) {this.details = 值；}公共双 getPrice() {退货价格；}公共无效setPrice(双值){this.price = 价值；}公共布尔 isStock() {退货；}公共无效setStock(布尔值){this.stock = 价值；}公共布尔 isMostWanted() {返回最想要的；}公共无效setMostWanted(布尔值){this.mostWanted = 价值；}@XmlAccessorType(XmlAccessType.FIELD)@XmlType(name = "", propOrder = {})公共静态类详细信息{@XmlElement(required = true)受保护的字符串突出显示；@XmlElement(required = true)受保护的字符串组合；公共字符串 getHighlights() {返回亮点；}public void setHighlights(String value) {this.highlights = 价值；}公共字符串 getComposition() {返回组合；}public void setComposition(String value) {this.composition = 值；}}@XmlAccessorType(XmlAccessType.FIELD)@XmlType(name = "", propOrder = {\u043c\u0443\u0436\u0441\u043a\u043e\u0439Or\u0416\u0435\u043d\u0441\u043a\u0438\u0439"})公共静态类性别{@XmlElementRefs({@XmlElementRef(name = "\u0436\u0435\u043d\u0441\u043a\u0438\u0439", namespace = "http://www.example.org/ShoesShop", type = JAXBElement.class, required = false),@XmlElementRef(name = "\u043c\u0443\u0436\u0441\u043a\u043e\u0439", namespace = "http://www.example.org/ShoesShop", type = JAXBElement.class, required = false)})protected List>男女不限;公共列表<JAXBElement<String>>getMaleOrFemale() {if (maleOrFemale == null) {maleOrFemale = new ArrayList>();}返回 this.maleOrFemale;}}@覆盖公共字符串 toString(){StringBuilder builder = new StringBuilder();builder.append("[title=");builder.append(title);builder.append(",brand=");builder.append(brand);builder.append(", category=");builder.append(category);builder.append(", season=");builder.append(季节);builder.append(", price=");builder.append(价格);builder.append("]");返回 builder.toString();}}

我还需要知道如何将接收到的数据写入新的 XML 文件中.

解决方案

UPDATED: 对原始答案的评论:

<块引用>

它不起作用，它给出了同样的错误

这意味着问题是因为 shoes 变量是 null，这很容易在 调试器 中看到.使用调试器可以为我们节省很多时间，所以请开始使用.

为了使 shoes 成为 null，代码似乎遇到了一个