JAVA开发基础知识：解析并创建XML文件和Java的反射

一、解析并创建xml文件

在使用Struts2框架时，在web.xml和struts.xml中都有xml代码，xml代码的主要作用就是配置，那在java中如何读取xml中的内容呢？

创建XmlAndReflect的Java项目，在项目中引入dom4j-1.6.1.jar文件，创建struts.xml文件，代码如下。

<mymvc>
<actions>
<action name="list" class="controller.List">
<result name="toListJSP">
</result>
<result name="toShowUserinfoList" type="redirect">
showUserinfoList.ghy
</result>
</action>

<action name="showUserinfoList" class="controller.ShowUserinfoList">
<result name="toShowUserinfoListJSP">
/showUserinfoList.jsp
</result>
</action>
</actions>
</mymvc>

创建Reader.java类，代码如下：

程序运行后的结果如下图：



上面我们读取并解析了xml文件，那如何创建xml文件呢？

创建Java类Writer.java代码如下。

package com.xml.test;

import java.io.FileWriter;

import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.XMLWriter;

public class Writer {

public static void main(String[] args) {

try{
Document document = DocumentHelper.createDocument();
Element mymvcElement = document.addElement("mymvc");
Element actionsElement = mymvcElement.addElement("actions");

Element listActionElement = actionsElement.addElement("action");
listActionElement.addAttribute("name", "list");
listActionElement.addAttribute("class", "controller.List");

Element toListJSPResultElemnt = listActionElement.addElement("result");
toListJSPResultElemnt.addAttribute("name", "toListJSP");
toListJSPResultElemnt.setText("/list.jsp");

Element toShowUserinfoListResultElement = listActionElement.addElement("result");
toShowUserinfoListResultElement.addAttribute("name", "toShowUserinfoList");
toShowUserinfoListResultElement.addAttribute("type","redirect");
toShowUserinfoListResultElement.setText("showUserinfoList.ghy");

Element showUserinfoListActionElement = actionsElement.addElement("action");
showUserinfoListActionElement.addAttribute("name", "showUserinfoList");
showUserinfoListActionElement.addAttribute("class", "controller.ShowUserinfoList");

Element toShowUserinfoListJSPResultElement = showUserinfoListActionElement.addElement("result");
toShowUserinfoListJSPResultElement.setText("/showUserinfoList.jsp");

OutputFormat format = OutputFormat.createPrettyPrint();
XMLWriter writer = new XMLWriter(new FileWriter("ghy.xml"),format);
writer.write(document);
writer.close();
}catch (Exception e) {
e.printStackTrace();
}
}

}

运行程序后，在当前项目中创建了名为ghy.xml的文件，文件内容如下：

二、Java的反射

反射技术可以对对象中的内容进行动态访问，在开发底层框架时经常使用到。

创建测试用的实体类Userinfo.java,代码如下。

package com.xml.test;

import java.util.Date;

public class Userinfo {

private int id;
private String username;
private String password;
private int age;
private Date insertDate;

public Userinfo(int id,String username,String password,int age){
super();
this.id = id;
this.username = username;
this.password = password;
this.age = age;
}

public Userinfo(){
super();
id=100;
username = "DaveBobo";
password = "123456";
age = 20;
insertDate = new Date();
}

public Userinfo(int id,String username,String password,int age,Date insertDate){
super();
this.id = id;
this.username = username;
this.password = password;
this.age = age;
this.insertDate = insertDate;
}

public String printDate(){
System.out.println("调用了printDate()无参方法！");
return "DaveBobo";
}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getUsername() {
return username;
}

public void setUsername(String username) {
this.username = username;
}

public String getPassword() {
return password;
}

public void setPassword(String password) {
this.password = password;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public Date getInsertDate() {
return insertDate;
}

public void setInsertDate(Date insertDate) {
this.insertDate = insertDate;
}
}

创建运行类Run.Java的代码如下：

package com.reflect.test;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

public class Run {

public static void main(String[] args) {

try{
//用3种方式获得Userinfo类的Class对象
Class<?>classRef1 = Class.forName("com.reflect.test.Userinfo");
Class<?>classRef2 = new Userinfo().getClass();
Class<?>classRef3 = Userinfo.class;
System.out.println("证明获取的类名称一模一样："+classRef1.getName()+
"--"+classRef2.getName()+"--"+classRef3.getName());

//使用Class类的newInstance()方法实例化Userinfo对象
Class<?>classRef = Userinfo.class.getClassLoader().loadClass("com.reflect.test.Userinfo");
Userinfo userinfoRef = (Userinfo)classRef.newInstance();
System.out.println("使用Class类的newInstance()方法调用无参的构造函数产生的默认值：id="
+userinfoRef.getId()+"username="
+userinfoRef.getUsername()+"password="
+userinfoRef.getPassword()+"age="
+userinfoRef.getAge()+"insertDate="
+userinfoRef.getInsertDate());

//使用Constructor类的newInstance()方法实例化Userinfo对象
Constructor<?> constructorUserinfo1 = classRef.getDeclaredConstructor(null);
Userinfo userinfoRef1 = (Userinfo)constructorUserinfo1.newInstance(null);
System.out.println("使用Constructor类的newInstance()调用无参的构造函数产生的默认值：id="
+userinfoRef1.getId()+"username="
+userinfoRef1.getUsername()+"password="
+userinfoRef1.getUsername()+"age="
+userinfoRef1.getAge()+"insertDate="
+userinfoRef1.getInsertDate());

//使用Constructor类的newInstance()方法实例化Userinfo对象
Constructor<?> constructorUserinfo2 = classRef.getConstructor(
int.class,String.class,String.class,int.class);
Userinfo userinfoRef2 = (Userinfo)constructorUserinfo2.newInstance(10,"DaveBobo","123456",20);
System.out.println("使用Constructor类的newInstance()方法调用有参的构造函数产生的默认值：id="
+userinfoRef2.getId()+"username="
+userinfoRef2.getUsername()+"password="
+userinfoRef2.getPassword()+"age="
+userinfoRef2.getAge());
System.out.println("打印通过反射对属性进行赋值的password："+userinfoRef2.getPassword());

//对无参方法进行反射调用
Method methodPrintDate = classRef.getDeclaredMethod("printDate");
System.out.println(methodPrintDate.invoke(userinfoRef));

}catch (Exception e) {
e.printStackTrace();
}
}

}
程序运行结果如下所示。
证明获取的类名称一模一样：com.reflect.test.Userinfo--com.reflect.test.Userinfo--com.reflect.test.Userinfo
使用Class类的newInstance()方法调用无参的构造函数产生的默认值：id=100username=DaveBobopassword=123456age=20insertDate=Sun Oct 23 21:45:24 CST 2016
使用Constructor类的newInstance()调用无参的构造函数产生的默认值：id=100username=DaveBobopassword=DaveBoboage=20insertDate=Sun Oct 23 21:45:25 CST 2016
使用Constructor类的newInstance()方法调用有参的构造函数产生的默认值：id=10username=DaveBobopassword=123456age=20
打印通过反射对属性进行赋值的password：123456
调用了printDate()无参方法！
DaveBobo