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1. XML文档说明
文档声明
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
1. <?xml ?>: 文档声明,必须位于第一行
2. version属性:xml文档的版本,必须有
3. encoding属性:字符集编码,非必须
4. standalone属性:是否独立(no 依赖外部文件),非必须
约束
在XML技术里,可以编写一个文档来约束一个XML文档的书写规范,这称之为XML约束。
常见的xml约束:DTD、Schema(XSD)
<!DOCTYPE HTMLPUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<note
xmlns="http://www.w3school.com.cn"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3school.com.cn note.xsd">
元素
元素(标签) element
1.举例: <bean></bean>
2.普通元素的结构开始标签、元素体、结束标签组成。例如:<name>zhangsan</name>
2.元素体:元素体可以是元素,也可以是文本,例如:<b><a>你好</a></b>
3.空元素:空元素只有开始标签,而没有结束标签,但元素必须自己闭合,例如:<c/>
4.元素命名:
(1)区分大小写
(2)不能使用空格,不能使用冒号:
(3)不建议以XML、xml、Xml开头
5.格式化良好的XML文档,必须只有一个根元素
属性
1.举例: <bean id="" className="">
2.属性是元素的一部分,它必须出现在元素的开始标签中
3. 属性的定义格式:属性名=属性值,其中属性值必须使用单引或双引
4.一个元素可以有0~N个属性,但一个元素中不能出现同名属性
5.属性名不能使用空格、冒号等特殊字符,且必须以字母开头
转义字符
< <
> >
" "
' '
& &
2. XML解析
2.1 常见的解析方式
开发中比较常见的解析方式有三种,如下:
1.DOM:要求解析器把整个XML文档装载到内存,并解析成一个Document对象。
(1)优点:元素与元素之间保留结构关系,故可以进行增删改查操作。
(2)缺点:XML文档过大,可能出现内存溢出显现。
2.SAX:
是一种速度更快,更有效的方法。它逐行扫描文档,一边扫描一边解析。
并以事件驱动的方式进行具体解析,每执行一行,都将触发对应的事件。(了解)
(1)优点:处理速度快,可以处理大文件
(2)缺点:只能读,逐行后将释放资源。
3.PULL:Android内置的XML解析方式,类似SAX。(了解)
2.2 DOM4J解析xml
- DOM4J是以dom方式解析。一个Java的XML API,具有性能优异、功能强大和极其易使用的特点,它的性能超过sun公司官方的dom技术.
- jar包:dom4j-1.6.1.jar
<?xml version="1.0" encoding="UTF-8" ?>
<students>
<student id="1">
<name>张三</name>
<age>18</age>
<gender>男</gender>
</student>
<student id="2">
<name>李四</name>
<age>17</age>
<gender>女</gender>
</student>
<student id="3">
<name>王五</name>
<age>22</age>
<gender>男</gender>
</student>
</students>
package xml_parse_dom4j;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import java.io.IOException;
import java.io.InputStream;
import java.util.Iterator;
import java.util.List;
public class Demo01 {
public static void main(String[] args) throws DocumentException, IOException {
//1.通过类加载器获取资源输入流对象
InputStream inputStream = Demo01.class.getClassLoader().getResourceAsStream("students.xml");
//2.创建org.dom4j.io包中的SAXReader对象
SAXReader saxReader = new SAXReader();
Document document = null;
try (inputStream) {
//3. 读取输入流 得到文档对象
document = saxReader.read(inputStream);
}
//4.拿到根元素
Element rootElement = document.getRootElement();
//5. 得到内部元素集合
List<Element> elements = rootElement.elements();
//6. 遍历 属性,值
for (Element element : elements) {
String s = null;
String name = element.getName();//拿到元素名
String id = element.attributeValue("id");//拿到元素的属性的值
s = "{" + name + ": " + "属性id=" + id;
List<Element> chileElements = element.elements();//元素的子元素集合
for (Element chileElement : chileElements) {
//遍历
String chileElementName = chileElement.getName();
String chileElementContent = chileElement.getText();//得到子元素内容
s += "\n\t\t" + chileElementName + "=" + chileElementContent + "}";
}
System.out.println(s);
}
}
}
2.3 XPath表达式解析XML
- 由于DOM4J在解析XML时只能一层一层解析,所以当XML文件层数过多时使用会很不方便,结合XPATH就可以直接获取到某个元素。
- 引入jar包:
jaxen-1.1.6.jar
- 在dom4j里面提供了两个方法,用来支持xpath
List<Node> selectNodes("xpath表达式"),用来获取多个节点
Node selectSingleNode("xpath表达式"),用来获取一个节点
xpath表达式
"nodename" 当前节点下的<nodename>元素节点
"/nodename" <文档节点>下的<nodename>元素节点
"//nodename" 全局匹配下的所有<nodename>元素节点
"/nodename1/nodename2" <文档节点>下的<nodename1>下的<nodename2>元素节点
"/nodename1//nodename2" <文档节点>下的<nodename1>下的(子、孙...)所有<nodename2>元素节点
"//@attribubeName" 全局匹配下的所有<attribubeName>属性节点
"/nodename1/nodename2[@id='1']" <文档节点>下的<nodename1>下的属性id=1的<nodename2>元素节点
XPath 语法|菜鸟教程 先别看中文解释,只看表达式,照着练练理解,再理解它的中文解释。
package xml_parse_xpath;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class Demo02 {
public static void main(String[] args) throws DocumentException, IOException {
//1.通过类加载器获取资源输入流对象
InputStream inputStream = Demo02.class.getClassLoader().getResourceAsStream("students.xml");
//2.创建org.dom4j.io包中的SAXReader对象
SAXReader saxReader = new SAXReader();
Document document = null;
try (inputStream) {
//3. 读取输入流 得到文档对象
document = saxReader.read(inputStream);
}
Element studentsElement = document.getRootElement();//<students>
Element studentElement = (Element) studentsElement.elements().get(0); //第一个<student>
//1. "nodename" 查询当前节点下的所有 "nodename" 子节点
System.out.println("\"nodename\"");
System.out.println(document.selectNodes("students")); //查询当前节点(document 文档节点)下的students子节点
//out: [org.dom4j.tree.DefaultElement@276438c9 [Element: <students attributes: []/>]]
System.out.println(studentsElement.selectNodes("students")); //查询<students>下的<students>
//out: []
System.out.println(studentElement.selectNodes("students")); //查询<student>下的students子节点
//out: []
System.out.println("==========================================================================");
//2. "/nodename" 查询<文档>节点下的<nodename>子节点,不管当前节点是谁 / 都从文档节点查
System.out.println("\"/nodename\"");
System.out.println(document.selectNodes("/students"));//查询<文档>下的<students>
//out: [org.dom4j.tree.DefaultElement@276438c9 [Element: <students attributes: []/>]]
System.out.println(studentsElement.selectNodes("/students")); //查询<文档>下的<students>
//out: [org.dom4j.tree.DefaultElement@276438c9 [Element: <students attributes: []/>]]
System.out.println(studentElement.selectNodes("/students")); //查询<文档>下的<students>
//out: [org.dom4j.tree.DefaultElement@276438c9 [Element: <students attributes: []/>]]
System.out.println("==========================================================================");
//3. "//nodename" 查询所有的<nodename>节点,全局匹配
System.out.println("\"//nodename\"");
System.out.println(document.selectNodes("//name"));
//out: [org.dom4j.tree.DefaultElement@701fc37a [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@31206beb [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@21a947fe [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@71248c21 [Element: <name attributes: []/>]]
System.out.println(studentsElement.selectNodes("//name"));
//out: [org.dom4j.tree.DefaultElement@701fc37a [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@31206beb [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@21a947fe [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@71248c21 [Element: <name attributes: []/>]]
System.out.println(studentElement.selectNodes("//name"));
//out: [org.dom4j.tree.DefaultElement@701fc37a [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@31206beb [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@21a947fe [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@71248c21 [Element: <name attributes: []/>]]
System.out.println("==========================================================================");
//4. "nodename1/nodename2" 查询当前节点下的<nodename1>下的<nodename2>节点
System.out.println("\"nodename1/nodename2\"");
System.out.println(document.selectNodes("students/student"));
//out: [org.dom4j.tree.DefaultElement@70beb599 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@15d9bc04 [Attribute: name id value "1"], org.dom4j.tree.DefaultAttribute@473b46c3 [Attribute: name u value "first"]]/>], org.dom4j.tree.DefaultElement@11e21d0e [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@516be40f [Attribute: name id value "2"]]/>], org.dom4j.tree.DefaultElement@37574691 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@3c0a50da [Attribute: name id value "3"], org.dom4j.tree.DefaultAttribute@646be2c3 [Attribute: name uid value "003"]]/>], org.dom4j.tree.DefaultElement@16267862 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@797badd3 [Attribute: name id value "4"], org.dom4j.tree.DefaultAttribute@77be656f [Attribute: name uid value "last"]]/>]]
System.out.println(studentsElement.selectNodes("students/student"));
//[]
System.out.println(studentElement.selectNodes("students/student"));
//[]
System.out.println("==========================================================================");
//5. "nodename1//nodename2" 查询当前节点下的<nodename1>后代中所有<nodename2>节点 , 在<nodename1>下全局匹配<nodename2>
System.out.println("\"nodename1//nodename2\"");
System.out.println(document.selectNodes("students//name"));
//[org.dom4j.tree.DefaultElement@701fc37a [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@31206beb [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@21a947fe [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@71248c21 [Element: <name attributes: []/>]]
System.out.println(studentsElement.selectNodes("student//name")); //<students> -> <students> -> <name>
//[org.dom4j.tree.DefaultElement@701fc37a [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@31206beb [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@21a947fe [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@71248c21 [Element: <name attributes: []/>]]
System.out.println(studentElement.selectNodes("//name"));
//[org.dom4j.tree.DefaultElement@701fc37a [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@31206beb [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@21a947fe [Element: <name attributes: []/>], org.dom4j.tree.DefaultElement@71248c21 [Element: <name attributes: []/>]]
System.out.println("==========================================================================");
//6. "//@id" 全局匹配属性名为id的属性节点
System.out.println("\"//@id\"");
System.out.println(document.selectNodes("//@id"));
//out: [org.dom4j.tree.DefaultAttribute@15d9bc04 [Attribute: name id value "1"], org.dom4j.tree.DefaultAttribute@516be40f [Attribute: name id value "2"], org.dom4j.tree.DefaultAttribute@3c0a50da [Attribute: name id value "3"], org.dom4j.tree.DefaultAttribute@797badd3 [Attribute: name id value "4"]]
System.out.println(studentsElement.selectNodes("//@id"));
//out: [org.dom4j.tree.DefaultAttribute@15d9bc04 [Attribute: name id value "1"], org.dom4j.tree.DefaultAttribute@516be40f [Attribute: name id value "2"], org.dom4j.tree.DefaultAttribute@3c0a50da [Attribute: name id value "3"], org.dom4j.tree.DefaultAttribute@797badd3 [Attribute: name id value "4"]]
System.out.println(studentElement.selectNodes("//@id"));
//out: [org.dom4j.tree.DefaultAttribute@15d9bc04 [Attribute: name id value "1"], org.dom4j.tree.DefaultAttribute@516be40f [Attribute: name id value "2"], org.dom4j.tree.DefaultAttribute@3c0a50da [Attribute: name id value "3"], org.dom4j.tree.DefaultAttribute@797badd3 [Attribute: name id value "4"]]
System.out.println(studentElement.selectNodes("@id"));// <student> -> id属性节点
//out: [org.dom4j.tree.DefaultAttribute@15d9bc04 [Attribute: name id value "1"]]
System.out.println("==========================================================================");
//7. "/students/student[age>18]" //得到age大于18的student元素节点数组
System.out.println(document.selectNodes("/students/student[age>18]"));
//out: [org.dom4j.tree.DefaultElement@37574691 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@3c0a50da [Attribute: name id value "3"], org.dom4j.tree.DefaultAttribute@646be2c3 [Attribute: name uid value "003"]]/>], org.dom4j.tree.DefaultElement@16267862 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@797badd3 [Attribute: name id value "4"], org.dom4j.tree.DefaultAttribute@77be656f [Attribute: name uid value "last"]]/>]]
System.out.println(studentsElement.selectNodes("/students/student[age>18]"));
//out: [org.dom4j.tree.DefaultElement@37574691 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@3c0a50da [Attribute: name id value "3"], org.dom4j.tree.DefaultAttribute@646be2c3 [Attribute: name uid value "003"]]/>], org.dom4j.tree.DefaultElement@16267862 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@797badd3 [Attribute: name id value "4"], org.dom4j.tree.DefaultAttribute@77be656f [Attribute: name uid value "last"]]/>]]
System.out.println(studentElement.selectNodes("/students/student[age>18]"));
//out: [org.dom4j.tree.DefaultElement@37574691 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@3c0a50da [Attribute: name id value "3"], org.dom4j.tree.DefaultAttribute@646be2c3 [Attribute: name uid value "003"]]/>], org.dom4j.tree.DefaultElement@16267862 [Element: <student attributes: [org.dom4j.tree.DefaultAttribute@797badd3 [Attribute: name id value "4"], org.dom4j.tree.DefaultAttribute@77be656f [Attribute: name uid value "last"]]/>]]
}
}
3. 解析XML并封装到类中
- 解析bean.xml文件 并 封装到Teacher类中
- bean.xml文件
<?xml version="1.0" encoding="UTF-8" ?>
<bean className="xml_parse_task.domain.Teacher">
<property name="name" value="张三"></property>
<property name="age" value="16"></property>
<property name="salary" value="88888.88"></property>
</bean>
- 实体类Teacher
package xml_parse_task.domain;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Teacher {
private String name;
private int age;
private double salary;
}
- 过程代码
package xml_parse_task;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import xml_parse_task.domain.Teacher;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
public class Demo02 {
public static void main(String[] args) throws DocumentException, IOException, NoSuchFieldException, InvocationTargetException, InstantiationException, IllegalAccessException, NoSuchMethodException {
method();
}
public static void method() throws DocumentException, IOException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException, NoSuchFieldException {
//解析xml dom4j+XPath
InputStream inputStream = Demo02.class.getClassLoader().getResourceAsStream("bean.xml");
SAXReader saxReader = new SAXReader();
Document document = saxReader.read(inputStream);
inputStream.close();
List<Element> list = document.selectNodes("/bean/property");
//Teacher.class 拿到字节码文件
Class<Teacher> teacherClass = Teacher.class;
//Teacher teacher = teacherClass.newInstance();
//得到空参构造器
Constructor<Teacher> constructor = teacherClass.getConstructor();
//创新Teacher对象
Teacher teacher = constructor.newInstance();
for (Element element : list) {
//根据name 获取字段
String name = element.attributeValue("name");
String value = element.attributeValue("value");
String mName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);
System.out.println(mName);
Field field = teacherClass.getDeclaredField(name);
Class<?> type = field.getType();
System.out.println(type);
if (type == int.class) {
Method method = teacherClass.getMethod(mName,int.class);
int i = Integer.parseInt(value);
method.invoke(teacher, i);
} else if (type == double.class) {
Method method = teacherClass.getMethod(mName,double.class);
double d = Double.parseDouble(value);
method.invoke(teacher, d);
} else if(type == String.class){
Method method = teacherClass.getMethod(mName,String.class);
method.invoke(teacher, value);
}else{
System.out.println("方法参数参数啥也不是");
}
}
System.out.println(teacher);
}
}
4. 参考资料
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