XML文件的解析
mybatis的学习当中，配置的加载传统的是通过解析用户配置的文件，获取到数据库连接与对象实体映射关系的，书中有描述到DOM\SAX\StAX 几种方案，一方面是夯实基础，一方面是了解三种方法的优缺点，今天就学习一下XML文件的解析
一、XML的解析方式
- DOM 解析XML底层接口之一,跨平台，跨语言
- SAX 解析XML底层接口之一
- Jdom/dom4J 基于底层API的封装，Java语言，更方便便捷
二、DOM解析
DOM 解析的原理：树形结构，依赖内存加载文件，树在内存中持久化存储，映射成Document对象，解析DOM树，识别父节点、当前节点、兄弟节点和子节点，在节点间游历，就能够获取到整棵树的数据。操作简易，消耗大，适用于小文档或者需要频繁修改文档的场景。
使用JDK自带的DocumentBuilderFactory进行解析
//生成工厂实例
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
//创建builder实例
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
//读取文件内容，加载入Document对象
Document document = documentBuilder.parse("store.xml");
//根据Name获取节点
NodeList productList = document.getElementsByTagName("product");
for(int i =0;i<productList.getLength();i++){
Node product = productList.item(i);
Node firstChild = product.getFirstChild();
Node lastChild = product.getLastChild();
String nodeName = product.getNodeName();
short nodeType = product.getNodeType();
String nodeValue = product.getNodeValue();
//获取节点内容
NamedNodeMap namedNodeMap = product.getAttributes();
for(int j=0;j<namedNodeMap.getLength();j++){
Node node = namedNodeMap.item(j);
String name = node.getNodeName();
String value = node.getNodeValue();
short type = node.getNodeType();
System.out.println("name:"+name+";value:"+value);
}
//获取子节点内容
NodeList childNodes = product.getChildNodes();
for(int k =0 ;k<childNodes.getLength();k++){
Node item = childNodes.item(k);
String itemNodeName = item.getNodeName();
short itemNodeType = item.getNodeType();
String itemNodeValue = item.getNodeValue();
System.out.println("itemName:"+itemNodeName+";itemValue:"+itemNodeValue);
NodeList children = item.getChildNodes();
for(int m =0;m<children.getLength();m++){
Node item1 = children.item(m);
System.out.println("itemName:"+item1.getNodeName()+";itemValue:"+item1.getNodeValue());
}
}
}
三、SAX解析
SAX解析原理：基于事件的模型，不需要将全部文档加载入内存，只需要用户读取的时候加载相应的内容片段即可，响应快，消耗小，适用于大型文档读取的场景。
使用JDK自带的SAXParserFactory
- 创建一个用于解析的Handler, 重写父类的关于片段解析的代码
public class SaxHandler extends DefaultHandler {
private List<Product> products = null;
private Product product;
private String currentTag = null;
private String currentValue = null;
private String nodeName = null;
public SaxHandler(String nodeName) {
this.nodeName = nodeName;
}
public List<Product> getProducts() {
return products;
}
@Override
public void startDocument() throws SAXException {
// 读到一个开始标签会触发
super.startDocument();
products = new ArrayList<Product>();
}
@Override
public void endDocument() throws SAXException {
//自动生成的方法存根
super.endDocument();
}
@Override
public void startElement(String uri, String localName, String name,
Attributes attributes) throws SAXException {
//文档的开头调用
super.startElement(uri, localName, name, attributes);
if (name.equals(nodeName)) {
product = new Product();
}
if (attributes != null && product != null) {
for (int i = 0; i < attributes.getLength(); i++) {
if (attributes.getQName(i).equals("id")) {
product.setId(Integer.valueOf(attributes.getValue(i)));
}
}
}
currentTag = name;
}
@Override
public void characters(char[] ch, int start, int length)
throws SAXException {
//处理在XML文件中读到的内容
super.characters(ch, start, length);
if (currentTag != null && product != null) {
currentValue = new String(ch, start, length);
if (!currentValue.trim().equals("") && !currentValue.trim().equals("\n")) {
if (currentTag.equals("name")) {
product.setName(currentValue);
} else if (currentTag.equals("price")) {
product.setPrice(Double.valueOf(currentValue));
}else if(currentTag.equals("inventory")){
product.setInventory(Integer.valueOf(currentValue));
}
}
}
currentTag = null;
currentValue = null;
}
@Override
public void endElement(String uri, String localName, String name)
throws SAXException {
// 结束标签的时候调用
super.endElement(uri, localName, name);
if (name.equals(nodeName)) {
products.add(product);
}
}
}
public class Product {
private Integer id;
private String name;
private Double price;
private Integer inventory;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Double getPrice() {
return price;
}
public void setPrice(Double price) {
this.price = price;
}
public Integer getInventory() {
return inventory;
}
public void setInventory(Integer inventory) {
this.inventory = inventory;
}
@Override
public String toString() {
return "Product{" +
"id=" + id +
", name='" + name + '\'' +
", price=" + price +
", inventory=" + inventory +
'}';
}
}
SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();
SAXParser saxParser = saxParserFactory.newSAXParser();
SaxHandler saxHandler = new SaxHandler("product");
saxParser.parse(new InputSource("store.xml"), saxHandler);
List<Product> products = saxHandler.getProducts();
products.forEach(System.out::println);
四、JDOM/Dom4J
<dependency>
<groupId>dom4j</groupId>
<artifactId>dom4j</artifactId>
<version>1.6.1</version>
</dependency>
SAXReader saxReader = new SAXReader();
Document document = saxReader.read(new File("store.xml"));
Element rootElement = document.getRootElement();
List<Element> elements = rootElement.elements();
List<Product> products = new ArrayList<>();
for(Element element : elements){
Integer id = Integer.valueOf(element.attributeValue("id"));
String name = element.element("name").getText();
Double price = Double.valueOf(element.element("price").getText());
Integer inventory = Integer.valueOf(element.elementText("inventory"));
Product product = new Product();
product.setId(id);
product.setName(name);
product.setPrice(price);
product.setInventory(inventory);
products.add(product);
}
products.forEach(System.out::println);
All codes are here：this page
