一,SAX的概述
SAX(XML的簡單API)是一種XML解析的替代方法。相比於DOM,SAX是一種速度更快,更有效的方法。它逐行掃描文檔,一邊掃描一邊解析。而且相比於DOM ,SAX可以在解析文檔的任意時刻停止解析,但任何事物都有其相反的一面,對於SAX來說就是操作複雜。
-
SAX的優點:
- 解析速度快
- 佔用內存少
-
SAX的缺點:
- 無法知道當前解析標籤(節點)的上層標籤,及其嵌套結構,僅僅知道當前解析的標籤的名字和屬性,要知道其他信息需要程序猿自己編碼
- 只能讀取XML,無法修改XML
- 無法隨機訪問某個標籤(節點)
- SAX解析適用場合
- 對於CPU資源寶貴的設備,如安卓等移動設備
- 對於只需從XML讀取信息而無需修改XML
二,SAX解析的步驟
解析步驟可分爲五步:
1,獲得sax解析工廠
SAXParserFactory factory = SAXParserFactory.newInstance();
2,解析工廠生產sax解析器
SAXParser saxParser = factory.newSAXParser();
3,根據解析工廠創建讀取器
XMLReader xmlReader = saxParser.getXMLReader();
4,根據讀取器設置事件處理器
xmlReader.setContentHandler(new MyHandler());
setContentHandler方法中的參數是ContentHandler的類型的是一個接口,由於接口不能直接新的對象,使用匿名內部類的辦法代碼過於冗長,想到使用其實現的子類的DefaultHandler需要實現的方法太多,從事我們應該想到適配器的概念。於是自己創建一個MyHandler類並擴展DefaultHandler覆蓋部分方法
.5,解析books.xml文件
xmlReader.parse(“xml / books.xml”);
三,實現代碼
(一)
Books.xml的代碼:
自定義SAX解析器:
public class MyHandler extends DefaultHandler {
private List<Bookorder> bookOrderList;
Bookorder bookOrder;
String text;
@Override
public void startDocument() throws SAXException {
// TODO Auto-generated method stub
super.startDocument();
System.out.println("books.xml文檔開始解析...");
}
@Override
public void endDocument() throws SAXException {
// TODO Auto-generated method stub
super.endDocument();
System.out.println("books.xml文檔解析結束...");
}
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
// TODO Auto-generated method stub
super.startElement(uri, localName, qName, attributes);
System.out.print("<" + qName);
//解析屬性
for (int i = 0; i < attributes.getLength(); i++) {
System.out.print(" " + attributes.getLocalName(i) + "=\""+ attributes.getValue(i) + "\"");
}
System.out.print(">");
}
@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
// TODO Auto-generated method stub
super.endElement(uri, localName, qName);
System.out.print("</" + qName + ">");
}
@Override
public void characters(char[] ch, int start, int length) throws SAXException {
// TODO Auto-generated method stub
super.characters(ch, start, length);
//打印標籤中的內容,按格式輸出
System.out.print(new String(ch, start, length));
}
}
測試解析XML文件:
//1、獲得sax解析工廠
SAXParserFactory factory = SAXParserFactory.newInstance();
//2、解析工廠生產sax解析器
SAXParser saxParser = factory.newSAXParser();
//3、根據解析工廠創建讀取器
XMLReader xmlReader = saxParser.getXMLReader();
//4、根據讀取器設置事件處理器
xmlReader.setContentHandler(new MyHandler2());
//5、解析books.xml文件
xmlReader.parse("xml/books.xml");
解析結果:
(二)解析XML文檔並將其封裝在JavaBean的對象中
的books.xml文檔:
編寫JavaBean的代碼
Bookorder1對象
package saxBean;
public class Bookorder1 {
private String id;
private String name;
private String author;
private String price;
public String getPrice() {
return price;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public void setPrice(String price) {
this.price = price;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
@Override
public String toString() {
return "Bookorder1 [id=" + id + ", name=" + name + ", author=" + author + ", price=" + price + "]";
}
}
自定義解析器:
package com.syj.sax;
import java.util.ArrayList;
import java.util.List;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import saxBean.Bookorder1;
public class MyHandler1 extends DefaultHandler {
private List<Bookorder1> bookOrderList;
private Bookorder1 bookOrder;
private String text;
@Override
public void startDocument() throws SAXException {
// TODO Auto-generated method stub
super.startDocument();
System.out.println("books.xml文檔開始解析...");
}
@Override
public void endDocument() throws SAXException {
// TODO Auto-generated method stub
super.endDocument();
for (Bookorder1 bookorder1 : bookOrderList) {
System.out.println(bookorder1);
}
System.out.println("books.xml文檔解析結束");
}
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
// TODO Auto-generated method stub
super.startElement(uri, localName, qName, attributes);
if ("books".equals(qName)) {
bookOrderList = new ArrayList<Bookorder1>();
} else if ("book".equals(qName)) {
bookOrder = new Bookorder1();
}
}
@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
// TODO Auto-generated method stub
super.endElement(uri, localName, qName);
if ("id".equals(qName)) {
bookOrder.setId(text);
} else if ("name".equals(qName)) {
bookOrder.setName(text);
} else if ("author".equals(qName)) {
bookOrder.setAuthor(text);
} else if ("price".equals(qName)) {
bookOrder.setPrice(text);
} else if ("book".equals(qName)) {
bookOrderList.add(bookOrder);
}
}
@Override
public void characters(char[] ch, int start, int length) throws SAXException {
// TODO Auto-generated method stub
super.characters(ch, start, length);
// 打印標籤中的內容,按格式輸出
text = new String(ch, start, length);
}
}
測試代碼:
public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException {
//1、獲得sax解析工廠
SAXParserFactory factory = SAXParserFactory.newInstance();
//2、解析工廠生產sax解析器
SAXParser saxParser = factory.newSAXParser();
//3、解析books.xml文件
saxParser.parse("xml/books.xml", new MyHandler1());
}
結果展示: