XML编程CRUD
XML解析技术概述
- XML解析方式分别两种:
- dom:(Document Object Model,即文档对象模型)W3C组织推荐的解析XML的一种方式。
- 缺点:内存消耗大
- 优点:对文档增查改删容易
- sax:(Simple API for XML)不是官方标准,但是XML社区事实上的标准,几乎所有的XML解析器都支持。
- 缺点:不适合对文档增查改删,只适合读取
- 优点:内存消耗小,解析速度快
- 网易云课堂:调整jvm内存大小
- jvm默认开辟64M内存
- dom:(Document Object Model,即文档对象模型)W3C组织推荐的解析XML的一种方式。
- XML解析开发板
- Jaxp(sun)、Jdom、dom4j
JAXP
- JAXP开发包是J2SE的一部分,它由java.xml、org.w3c.dom、org.xml.sax包及其子包组成。
- 在javax.xml.parsers包中,定义了几个工厂类,程序员调用这些工厂类,可以得到xml文件的DOM或SAX的解析器,从而实现对xml文档的解析。
使用JAXP进行DOM解析
- javax.xml.parsers包中的DocumentBuilderFactory用于创建DOM模式的解析器对象,DocumentBuilderFactory是一个抽象工厂类,它不能直接实例化,但该类提供了一个newInstance方法,这个方法会根据本地平台默认安装的解析器,自动创建一个工厂的对象并返回。
- dom解析下,xml文档的每一个组成部分都会用一个对象表示,例如标签用Element、属性用Attr、但不管什么对象,都是Node的子类,在开发中可以把获取到的任意节点都当作Node对待。
Demo1.java
package cn.itcast.xml;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
public class Demo1 {
public static void main(String[] args) throws Exception{
//创建工程
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
//得到dom解析器
DocumentBuilder builder = factory.newDocumentBuilder();
//解析xml文档,得到代表文档的document
Document document = builder.parse("src/book.xml");
}
}
更新XML文件
- javax.xml.transform包中的Transformer类用于把代表XML文件的Document对象转换为某种格式后进行输出,例如把xml文件应用样式表后转成一个html文档。利用这个对象,当然也可以把Document对象又重新写入到一个XML文件中。
- Transformer类通过transform方法完成转换操作,该方法接收一个源和一个目的地。
- javax.xml.transform.dom.DOMSource类来关联要转换的document对象
- 用javax.xml.transform.stream.StreamResult对象来表示数据的目的地
- Transformer对象通过TransformerFactory获得。
DOM方式解析XML文件
- DOM解析编程:
- 遍历所有节点
- 查找某一个节点
- 删除节点
- 更新节点
- 添加节点
- 编程练习:
Demo2.java
package cn.itcast.xml;
import java.io.FileOutputStream;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
//使用dom方式对xml文档进行crud
public class Demo2 {
//读取xml文档中:<书名>JavaScript网页开发</书名> 节点中的值
@Test
public void read1() throws Exception {
//创建工程
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
//得到dom解析器
DocumentBuilder builder = factory.newDocumentBuilder();
//解析xml文档,得到代表文档的document
Document document = builder.parse("src/book.xml");
NodeList list = document.getElementsByTagName("书名");
Node node = list.item(1);
String content = node.getTextContent();
System.out.println(content);
}
//读取xml文档中的所有标签
@Test
public void read2() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
//得到根节点
Node root = document.getElementsByTagName("书架").item(0);
list(root);
}
public void list(Node node) {
if(node instanceof Element) {
System.out.println(node.getNodeName());
}
NodeList list = node.getChildNodes();
for(int i = 0; i < list.getLength(); i ++) {
Node child = list.item(i);
list(child);
}
}
//读取xml文档中标签属性的值:<书名 name="xxxx">Java就业培训教程</书名>
@Test
public void read3() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
Element bookname = (Element) document.getElementsByTagName("书名").item(0);
String value = bookname.getAttribute("name");
System.out.println(value);
}
//向xml文档中添加节点:<售价>59.00元</售价>
@Test
public void add1() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
//创建节点
Element price = document.createElement("售价");
price.setTextContent("59.00元");
//把创建的节点挂到第一本书上
Element book = (Element) document.getElementsByTagName("书").item(0);
book.appendChild(price);
//把更新后内存写回xml文档
TransformerFactory tffactory = TransformerFactory.newInstance();
Transformer tf = tffactory.newTransformer();
tf.transform(new DOMSource(document), new StreamResult(new FileOutputStream("src/book.xml")));
}
//向xml文档中指定位置添加节点:<售价>59.00元</售价>
@Test
public void add2() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
//创建节点
Element price = document.createElement("售价");
price.setTextContent("59.00元");
//得到参考节点
Element refNode = (Element) document.getElementsByTagName("售价").item(0);
//得到要挂新节点的节点
Element book = (Element) document.getElementsByTagName("书").item(0);
//往book节点的指定位置插入新节点
book.insertBefore(price, refNode);
//把更新后内存写回xml文档
TransformerFactory tffactory = TransformerFactory.newInstance();
Transformer tf = tffactory.newTransformer();
tf.transform(new DOMSource(document), new StreamResult(new FileOutputStream("src/book.xml")));
}
//向xml文档节点添加属性:<书名>Java就业培训教程</书名> 添加name="xxxx"
@Test
public void addAttr() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
Element bookname = (Element) document.getElementsByTagName("书名").item(0);
bookname.setAttribute("name", "xxxx");
//把更新后内存写回xml文档
TransformerFactory tffactory = TransformerFactory.newInstance();
Transformer tf = tffactory.newTransformer();
tf.transform(new DOMSource(document), new StreamResult(new FileOutputStream("src/book.xml")));
}
//向xml文档中删除节点:<售价>59.00元</售价>
@Test
public void delete1() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
//得到要删除的节点
Element e = (Element) document.getElementsByTagName("售价").item(0);
//得到要删除节点的父节点
Element book = (Element) document.getElementsByTagName("书").item(0);
//父节点删除节点
book.removeChild(e);
//把更新后内存写回xml文档
TransformerFactory tffactory = TransformerFactory.newInstance();
Transformer tf = tffactory.newTransformer();
tf.transform(new DOMSource(document), new StreamResult(new FileOutputStream("src/book.xml")));
}
//向xml文档中删除节点:<售价>59.00元</售价>
@Test
public void delete2() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
//得到要删除的节点
Element e = (Element) document.getElementsByTagName("售价").item(0);
e.getParentNode().removeChild(e);
// e.getParentNode().getParentNode().removeChild(e.getParentNode()); //将需删除节点的父节点删除
//把更新后内存写回xml文档
TransformerFactory tffactory = TransformerFactory.newInstance();
Transformer tf = tffactory.newTransformer();
tf.transform(new DOMSource(document), new StreamResult(new FileOutputStream("src/book.xml")));
}
//更新售价
@Test
public void updata() throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("src/book.xml");
Element e = (Element) document.getElementsByTagName("售价").item(0);
e.setTextContent("109元");
//把更新后内存写回xml文档
TransformerFactory tffactory = TransformerFactory.newInstance();
Transformer tf = tffactory.newTransformer();
tf.transform(new DOMSource(document), new StreamResult(new FileOutputStream("src/book.xml")));
}
}