SAX方式解析XML原理

SAX的工作方式簡單地說就是對文件進行順序掃描，當掃描到文件（document）開始與結束,元素（Element）開始與結束、文件（document）結束等地方時通知事件處理函式，由事件處理函式做相應的動作，然後繼續同樣的掃描，直至文件結束。

優點：消耗資源比較少；適合大檔案解析；

缺點：只能讀取不能修改；開發複雜；

SAX方式解析XML示例

1 <?xml version="1.0" encoding="UTF-8"?>
2 <student id="001">
3     <name>張三</name>
4     <
 
sex>男</sex>
5     <age>20</age>
6 </student>

SAX01解析：

 1 package com.java1234.xml;
 2 
 3 import javax.xml.parsers.ParserConfigurationException;
 4 import javax.xml.parsers.SAXParser;
 5 import javax.xml.parsers.SAXParserFactory;
 6 
 7 import org.xml.sax.Attributes;
 8 import org.xml.sax.SAXException;
 
 9 import org.xml.sax.helpers.DefaultHandler;
10 
11 public class SAX01 extends DefaultHandler{
12 
13     @Override
14     public void startDocument() throws SAXException {
15         // TODO Auto-generated method stub
16         System.out.println("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
17
 
     }
18 
19     @Override
20     public void endDocument() throws SAXException {
21         // TODO Auto-generated method stub
22         System.out.println("文件載入完畢！");
23     }
24 
25     @Override
26     public void startElement(String uri, String localName, String qName, 
27             Attributes attributes) throws SAXException {
28         // TODO Auto-generated method stub
29         System.out.println("元素節點開始載入"+qName);
30     }
31 
32     @Override
33     public void endElement(String uri, String localName,
34             String qName) throws SAXException {
35         // TODO Auto-generated method stub
36         System.out.println("元素節點結束載入"+qName);
37     }
38 
39     @Override
40     public void characters(char[] ch, int start, int length) throws SAXException {
41         // TODO Auto-generated method stub
42         System.out.println("掃描文字節點"+new String(ch,start,length));
43     }
44     
45     public static void main(String[] args) throws Exception {
46         SAXParserFactory factory=SAXParserFactory.newInstance();
47         SAXParser parser=factory.newSAXParser();
48         parser.parse("src/demo01.xml", new SAX01());
49     }
50 }

解析更加複雜的資訊；例如形成一個類重新輸出類裡面的數值啥的！

Student類

 1 package com.java1234.model;
 2 
 3 public class Student {
 4     private String name;
 5     private String sex;
 6     private String id;
 7     private int age;
 8     public String getName() {
 9         return name;
10     }
11     public void setName(String name) {
12         this.name = name;
13     }
14     public String getSex() {
15         return sex;
16     }
17     public void setSex(String sex) {
18         this.sex = sex;
19     }
20     public String getId() {
21         return id;
22     }
23     public void setId(String id) {
24         this.id = id;
25     }
26     public int getAge() {
27         return age;
28     }
29     public void setAge(int age) {
30         this.age = age;
31     }
32     @Override
33     public String toString() {
34         // TODO Auto-generated method stub
35         return this.id+","+this.name+","+this.age+","+this.sex;//重寫toString 方法
36     }
37     
38 }

XML如下：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <students>
 3     <student id="001">
 4         <name>張三</name>
 5         <sex>男</sex>
 6         <age>20</age>
 7     </student>
 8     <student id="002">
 9         <name>李四</name>
10         <sex>女</sex>
11         <age>18</age>
12     </student>
13 </students>

 1 package com.java1234.xml;
 2 
 3 import java.util.ArrayList;
 4 import java.util.List;
 5 
 6 import javax.xml.parsers.ParserConfigurationException;
 7 import javax.xml.parsers.SAXParser;
 8 import javax.xml.parsers.SAXParserFactory;
 9 import org.xml.sax.Attributes;
10 import org.xml.sax.SAXException;
11 import org.xml.sax.helpers.DefaultHandler;
12 
13 import com.java1234.model.Student;
14 
15 public class SAX3 extends DefaultHandler{
16     private List<Student>students=null;
17     private Student student=null;
18     private String tag=null;//標記上一個節點
19     
20     @Override
21     public void startDocument() throws SAXException {
22         // TODO Auto-generated method stub
23         System.out.println("開始讀取學生資訊");
24         students=new ArrayList<Student>();
25     }
26 
27     @Override
28     public void endDocument() throws SAXException {
29         // TODO Auto-generated method stub
30         System.out.println("\n 學生資訊讀取完畢");
31     }
32 
33     @Override
34     public void startElement(String uri, String localName, String qName, 
35             Attributes attributes) throws SAXException {
36         // TODO Auto-generated method stub
37         //attributes 屬性節點操作
38         if("student".equals(qName)){
39             student=new Student();
40             student.setId(attributes.getValue(0));
41         }
42         tag=qName;
43     }
44 
45     @Override
46     public void endElement(String uri, String localName,
47             String qName) throws SAXException {
48         // TODO Auto-generated method stub
49         if("student".equals(qName)){
50             students.add(student);
51             student=null;
52         }
53         tag=null;
54     }
55 
56     @Override
57     public void characters(char[] ch, int start, int length) throws SAXException {
58         // TODO Auto-generated method stub
59         if(tag!=null){
60             String content=new String(ch,start,length);
61             if("name".equals(tag)){
62                 student.setName(content);
63             }else if("age".equals(tag)){
64                 student.setAge(Integer.parseInt(content));
65             }else if("sex".equals(tag)){
66                 student.setSex(content);
67             }
68         }
69     }
70     
71     public static void main(String[] args) throws Exception {
72         SAXParserFactory factory=SAXParserFactory.newInstance();
73         SAXParser parser=factory.newSAXParser();
74         SAX3 sax3=new SAX3();
75         parser.parse("src/students.xml", sax3);
76         for(Student s:sax3.students){
77             System.out.println(s);
78         }
79     }
80     
81     
82     
83 }

結果如下所示：