反射技術動態獲取屬性
知道struts2的流程的鄉親們都知道。struts2採用了動態獲取屬性的方法，
將表單裏的數據傳給了Action。
將表單裏的數據傳給了Action。
例如;
在struts2裏有如下配置文件
在struts2裏有如下配置文件
<action name="MyAction" class="com.lin.test.ActionTest" method="execute">
<result name="success">success.jsp</result>
<result name="fail">fail.jsp</result>
<result name="fail">fail.jsp</result>
</action>
com.lin.test.ActionTest的實現如下：
package com.lin.test;
package com.lin.test;
public class ActionTest {
private String userName;
private String passWord;
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 String execute(){
if((userName==null)||(userName.equals("")))
{
System.out.println("text爲空。。。。");
return "fail";
}else{
System.out.println("username: "+userName);
return "success";
}
}
}
private String userName;
private String passWord;
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 String execute(){
if((userName==null)||(userName.equals("")))
{
System.out.println("text爲空。。。。");
return "fail";
}else{
System.out.println("username: "+userName);
return "success";
}
}
}
把test.jsp文件的表單數據提交給struts2 配置的Action裏，這裏叫做MyAction
<%@ page language="java" contentType="text/html; charset=GB18030"
pageEncoding="GB18030"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>登陸</title>
</head>
<body>
<s:form action="MyAction" method="post">
<s:textfield label="用戶名" name="userName"/><!--標籤的name 屬性是針對於後臺，id是對前臺-->
<s:textfield label="密碼" name="passWord"/>
<s:submit value="提交"/>
</s:form>
</body>
</html>
pageEncoding="GB18030"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>登陸</title>
</head>
<body>
<s:form action="MyAction" method="post">
<s:textfield label="用戶名" name="userName"/><!--標籤的name 屬性是針對於後臺，id是對前臺-->
<s:textfield label="密碼" name="passWord"/>
<s:submit value="提交"/>
</s:form>
</body>
</html>
測試：
輸入用戶名後點擊確定，Action的java代碼裏在控制檯裏成功的輸出的text的值
若text的內容爲空
點擊確定後，由於在Action的方法裏對輸入的內容進行了判斷，此時輸出
text爲空。
通過以上例子，Action獲取了輸入的值，並且進行了判斷。
那麼這個原理是怎麼實現的呢？
答案：反射機制
，對於任意一個類，都能夠知道這個類的所有屬性和方法；對於任意一個對象，都能夠調用它的任意一個方法。
demo
User類，加上tostring方法，方便打印
class User {
public User(){}
public User(){}
private String username;
private String userid;
public String getUserid() {
return userid;
}
return userid;
}
@Override
public String toString() {
return "User [username=" + username + ", userid=" + userid + "]";
}
public String toString() {
return "User [username=" + username + ", userid=" + userid + "]";
}
public void setUserid(String userid) {
this.userid = userid;
}
this.userid = userid;
}
public String getUsername() {
return username;
}
return username;
}
public void setUsername(String username) {
this.username = username;
}
}
this.username = username;
}
}
public class Reflect {
public static void main(String[] args) throws Exception {
//創建user1對象
User user1 = new User();
user1.setUsername("arthinking");
user1.setUserid("001");
String username = "arthinking";
String userid = "001";
//通過user1對象獲取Class
Class<?> classType = user1.getClass();
public static void main(String[] args) throws Exception {
//創建user1對象
User user1 = new User();
user1.setUsername("arthinking");
user1.setUserid("001");
String username = "arthinking";
String userid = "001";
//通過user1對象獲取Class
Class<?> classType = user1.getClass();
//生成user2對象
Object user2 = classType.getConstructor(new Class[]{}).newInstance(new Object[]{});
//從user1對應的Class對象中獲取所有的屬性
Field[] fields = classType.getDeclaredFields();
for(int i=0; i<fields.length; i++){
Object user2 = classType.getConstructor(new Class[]{}).newInstance(new Object[]{});
//從user1對應的Class對象中獲取所有的屬性
Field[] fields = classType.getDeclaredFields();
for(int i=0; i<fields.length; i++){
Field field = fields;
//動態生成getter和setter方法
String fieldName = field.getName();
String firstChar = fieldName.substring(0,1).toUpperCase();
//動態生成getter和setter方法
String fieldName = field.getName();
String firstChar = fieldName.substring(0,1).toUpperCase();
String getterName = "get" + firstChar + fieldName.substring(1);
String setterName = "set" + firstChar + fieldName.substring(1);
Method getter = classType.getMethod(getterName);
String setterName = "set" + firstChar + fieldName.substring(1);
Method getter = classType.getMethod(getterName);
Method setter = classType.getMethod(setterName, new Class[]{field.getType()});
Object result = getter.invoke(user1);
setter.invoke(user2, new Object[]{result});
}
Object result = getter.invoke(user1);
setter.invoke(user2, new Object[]{result});
}
Syso（“User1”+user1）；
System.out.println("user2 "+user2);
}
System.out.println("user2 "+user2);
}
}
有相同的輸出
有相同的輸出