Struts2中Action对象的set方法和get方法调用规则

    Struts的Action是采用的是多实例多线程设计，而不是像Servlet那样采用单实例多线程设计，因此在struts中，一个请求就对应一个Action对象，个对象之间的数据相互之间互不干扰。没接到一个新的请求，就产生一个新的Action对象，并对Action对象的各属性赋予默认初始值。之后再根据一定的规则调用set方法给各属性赋值，并根据一定规则调用get方法。也就是说，Action对象不是一开始就必须调用set方法的。本文重点讲Action对象调用set和get方法的规则：

1.get方法的调用规则

    Action对象get方法的调用规则相对简单，因此先说get方法的调用规则。调用get方法方法是为了获取属性值，这一点不仅仅在struts中是这样，在任何java程序中，都是这样的。那么什么时候才需要一个Action对象的属性值呢？就目前本人探索和总结的结果来看，分为以下三种情况：

（一）、在Action请求转发到下一个Action时（即result的type属性为chain时），下一个Action有对应属性的set方法；

    这种情况是为了传递数据，让数据跟着Action流程的流转而进入到下一个Action对象，因此是非常重要的。但是呢，这种传递不一定能达到想要的目的，意外出现在如果最初的http请求本身就有了对应的查询参数值，则目标Action会在获得了源Action的get值之后，再次去过的请求的查询参数值，并用这个值作为set方法的传入参数，在这种情况下，目标Filed的值还是http请求的查询参数值。

（二）、在struts.xml配置文件中引用了相应的Action属性；

    这种情况其实是显式调用了get方法，所以一定会被调用，也没什么好说的。

（三）有对应的request.getAttribute()，且之前没有用过相应的request.setAttribute()。

   这里说的request.getAttribute()一般出现在视图中，比如jsp的requestScope.filedName，或者显示的request.getAttribute() java 代码。

  Action对象get方法调用的具体规则流程如下：

需要强调的是，只有在真正需要数据的时候，才会调用get方法，而不是在离开Action的时候。所以，在下一个Action的拦截器之后，到达Action时，上一个Action的get方法才被调用（因为这时需要给目标Action赋值了，而赋值需要值的来源，所以就要调用上一个Action的get方法以获得赋值的来源）。

还有需要强调的是，需要get方法时，总是调用最近Action对象的get方法，如果最近的Action没有get方法，则调用次近的，知道最开始的那个Action。

2.set方法的调用规则

    Action对象set方法的调用规则相对于get方法来说比较复杂。同样，在任何java程序中，set方法都是为了给对象的属性赋值，因此，set方法的调用规则关乎到Action对象的数据是怎么获取的，因此显得尤为重要。

    因为set方法是给Action对象数据赋值的，所以，要知道set方法的调用规则，首先要清楚Action对象的属性数据的来源有哪些。就本人目前探索和总结来看，Action对象的属性数据的来源有以下两类：（1）上一个Action的get方法、（2）http请求参数。这两类数据来源也就对应了set方法的调用规则。

（一）从源Action的get方法中获得

    这种情况对应于get方法调用规则中的第一种情况，也是在Action转发时发生的，而且和get方法的第一种情况总是同时发生的，也就是说，这两张情况要么都发生，要么都不发生。两种情况共同完成Action对象的数据传递。

（二）从请求参数中来

    如果有对应的请求参数值，则这种情况一定会发生，及时上一种情况已经发生过了。这样，如果源Action有对应的get方法，请求中也有对应的请求参数值（注意是getParameter到的值，而不是getAttribute到的值，Action是不能从request的Attribute中得到属性值的），则一个get方法会被调用两次，后面一次获取的是请求参数中的值，最终的属性值和请求参数一致。

    set方法调用规则的流程如下：

测试用的代码如下：LoginAction是源Action，LoginAction2是目标Action。

 1 import com.opensymphony.xwork2.ActionSupport;
 2 import org.apache.logging.log4j.LogManager;
 3 import org.apache.logging.log4j.Logger;
 4 import org.apache.struts2.ServletActionContext;
 5 
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 
 9 public class LoginAction2 extends ActionSupport{
10     private final Logger log = LogManager.getLogger(getClass());
11     private String username;
12     private String password;
13     private String usernameAndPassword;
14     private int age;
15 
16     public String getUsername() {
17         log.trace("getUsername is in invoked");
18 
19         return username;
20     }
21 
22     public void setUsername(String username) {
23         log.trace("setUsername is in invoked");
24 
25         this.username = username;
26     }
27 
28     public String getPassword() {
29         return password;
30     }
31 
32     public void setPassword(String password) {
33         this.password = password;
34     }
35 
36     public String getUsernameAndPassword() {
37         log.trace("getUsernameAndPassword is in invoked");
38 
39         return usernameAndPassword;
40     }
41 
42     public void setUsernameAndPassword(String usernameAndPassword) {
43         log.trace("setUsernameAndPassword is in invoked");
44 
45         this.usernameAndPassword = usernameAndPassword;
46     }
47 
48     @Override
49     public void validate() {
50         log.trace("validate is invoked");
51         HttpServletRequest request = ServletActionContext.getRequest();
52         HttpServletResponse response = ServletActionContext.getResponse();
53         System.out.println( request.getAttribute("age"));
54     }
55 
56     public int getAge() {
57         log.trace("getAge is invoked");
58         System.out.println("getAge:  "+age);
59 
60         return 70;
61     }
62 
63 //    public void setAge(int age) {
64 //        log.trace("setAge is invoked");
65 //        System.out.println("setAge:  "+age);
66 //        this.age = age;
67 //    }
68 }
  1 package edu.whu.swe.learnstruts2;
  2 
  3 import com.opensymphony.xwork2.ActionContext;
  4 import com.opensymphony.xwork2.ActionSupport;
  5 import edu.whu.swe.learnstruts2.service.LoginService;
  6 import edu.whu.swe.learnstruts2.service.impl.LoginServiceImpl;
  7 import org.apache.logging.log4j.LogManager;
  8 import org.apache.logging.log4j.Logger;
  9 import org.apache.struts2.ServletActionContext;
 10 
 11 import javax.servlet.RequestDispatcher;
 12 import javax.servlet.ServletContext;
 13 import javax.servlet.http.HttpServletRequest;
 14 import javax.servlet.http.HttpServletResponse;
 15 
 16 
 17 public class LoginAction extends ActionSupport {
 18     private final Logger log = LogManager.getLogger(getClass());
 19     private String username;
 20     private String password;
 21     private String alianname;
 22     private String othertest;
 23     private int age;
 24 
 25     private final LoginService loginService = new LoginServiceImpl();
 26 
 27 
 28     public String execute() throws Exception {
 29 
 30 
 31         if (!loginService.isLogin(username, password)) {
 32 
 33             return INPUT;
 34 
 35         }
 36         HttpServletRequest request = ServletActionContext.getRequest();
 37         HttpServletResponse response = ServletActionContext.getResponse();
 38 //        request.setAttribute("age", 22);
 39 //        this.age=22;
 40 
 41 /** 因为是使用的框架，所以重定向语句之后的代码依旧会执行，但是业务逻辑已经转到定向后的地方了 */
 42 //        ServletContext context =request.getSession().getServletContext();
 43 //        RequestDispatcher dispatcher=context.getRequestDispatcher("/usernameInvalide.jsp");
 44 //        System.out.println("print this before dispatcher");
 45 //        dispatcher.forward(request,response);
 46 //        System.out.println("print this after dispatcher");
 47 //        age+=1000;
 48 
 49 
 50         //
 51         System.out.println("LoginAction is executed");
 52         return SUCCESS;
 53 
 54     }
 55 
 56     public String getUsernameAndPassword() {
 57         log.trace("getUsernameAndPassword is in invoked");
 58         return username + password;
 59     }
 60 
 61     public void setUsernameAndPassword(String usernameAndPassword) {
 62         log.trace("setUsernameAndPassword is in invoked");
 63 
 64     }
 65 
 66 
 67     public String getUsername() {
 68         log.trace("getUsername is in invoked");
 69         return username;
 70     }
 71 
 72     public void setUsername(String username) {
 73         log.trace("setUsername is in invoked");
 74         this.username = username;
 75     }
 76 
 77     public String getPassword() {
 78         return password;
 79     }
 80 
 81     public void setPassword(String password) {
 82         this.password = password;
 83     }
 84 
 85 
 86     public String getAlianame() {
 87         log.trace("getAlianame is in invoked");
 88 
 89         return alianname;
 90     }
 91 
 92     public void setAlianame(String alianname) {
 93         log.trace("setAlianame is in invoked");
 94 
 95         this.alianname = alianname;
 96     }
 97 
 98     public String getOthertest() {
 99         return othertest;
100     }
101 
102     public void setOthertest(String othertest) {
103         this.othertest = othertest;
104     }
105 
106 
107     @Override
108     public void validate() {
109         log.trace("validate is invoked");
110     }
111 
112     public void setAge(int age) {
113         log.trace("setAge is invoked");
114         this.age = age + 33;
115     }
116 
117     public int getAge() {
118         log.trace("setAge is invoked");
119         return 55;
120     }
121 }

关键的struts.xml配置如下：

<action name="login1" class="edu.whu.swe.learnstruts2.LoginAction2">
            <result name="success">/welcome.jsp</result>
</action>


<action name="login" class="edu.whu.swe.learnstruts2.LoginAction">
            <result name="success" type="chain">
                <param name="actionName">login1</param>
                <param name="namespace">/</param>
            </result>
</action>

 测试结果如下：

不输入age
2018-01-12 16:34:58.876 TRACE edu.whu.swe.learnstruts2.LoginAction setUsername - " setUsername is in invoked " 
2018-01-12 16:34:58.877 TRACE edu.whu.swe.learnstruts2.LoginAction validate - " validate is invoked " 
LoginAction is executed
2018-01-12 16:34:58.877 TRACE edu.whu.swe.learnstruts2.LoginAction getAge - " setAge is invoked " 
2018-01-12 16:34:58.878 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
2018-01-12 16:34:58.878 TRACE edu.whu.swe.learnstruts2.LoginAction getUsername - " getUsername is in invoked " 
2018-01-12 16:34:58.878 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:34:58.878 TRACE edu.whu.swe.learnstruts2.LoginAction getUsernameAndPassword - " getUsernameAndPassword is in invoked " 
2018-01-12 16:34:58.879 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsernameAndPassword - " setUsernameAndPassword is in invoked " 
2018-01-12 16:34:58.879 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:34:58.880 TRACE edu.whu.swe.learnstruts2.LoginAction2 validate - " validate is invoked " 
2018-01-12 16:34:58.883 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsername - " getUsername is in invoked " 
2018-01-12 16:34:58.883 TRACE edu.whu.swe.learnstruts2.LoginAction2 getAge - " getAge is invoked " 
2018-01-12 16:34:58.884 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsernameAndPassword - " getUsernameAndPassword is in invoked " 

输入了age
2018-01-12 16:35:36.356 TRACE edu.whu.swe.learnstruts2.LoginAction setAge - " setAge is invoked " 
2018-01-12 16:35:36.356 TRACE edu.whu.swe.learnstruts2.LoginAction setUsername - " setUsername is in invoked " 
2018-01-12 16:35:36.357 TRACE edu.whu.swe.learnstruts2.LoginAction validate - " validate is invoked " 
LoginAction is executed
2018-01-12 16:35:36.358 TRACE edu.whu.swe.learnstruts2.LoginAction getAge - " setAge is invoked " 
2018-01-12 16:35:36.358 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
2018-01-12 16:35:36.358 TRACE edu.whu.swe.learnstruts2.LoginAction getUsername - " getUsername is in invoked " 
2018-01-12 16:35:36.359 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:35:36.359 TRACE edu.whu.swe.learnstruts2.LoginAction getUsernameAndPassword - " getUsernameAndPassword is in invoked " 
2018-01-12 16:35:36.359 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsernameAndPassword - " setUsernameAndPassword is in invoked " 
2018-01-12 16:35:36.360 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
2018-01-12 16:35:36.360 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:35:36.360 TRACE edu.whu.swe.learnstruts2.LoginAction2 validate - " validate is invoked " 
2018-01-12 16:35:36.363 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsername - " getUsername is in invoked " 
2018-01-12 16:35:36.363 TRACE edu.whu.swe.learnstruts2.LoginAction2 getAge - " getAge is invoked " 
2018-01-12 16:35:36.363 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsernameAndPassword - " getUsernameAndPassword is in invoked " 


没有age表单
2018-01-12 16:37:41.549 TRACE edu.whu.swe.learnstruts2.LoginAction setUsername - " setUsername is in invoked " 
2018-01-12 16:37:41.591 TRACE edu.whu.swe.learnstruts2.LoginAction validate - " validate is invoked " 
LoginAction is executed
2018-01-12 16:37:41.610 TRACE edu.whu.swe.learnstruts2.LoginAction getAge - " setAge is invoked " 
2018-01-12 16:37:41.611 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
2018-01-12 16:37:41.611 TRACE edu.whu.swe.learnstruts2.LoginAction getUsername - " getUsername is in invoked " 
2018-01-12 16:37:41.611 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:37:41.612 TRACE edu.whu.swe.learnstruts2.LoginAction getUsernameAndPassword - " getUsernameAndPassword is in invoked " 
2018-01-12 16:37:41.612 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsernameAndPassword - " setUsernameAndPassword is in invoked " 
2018-01-12 16:37:41.615 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:37:41.622 TRACE edu.whu.swe.learnstruts2.LoginAction2 validate - " validate is invoked " 
2018-01-12 16:37:41.741 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsername - " getUsername is in invoked " 
2018-01-12 16:37:41.741 TRACE edu.whu.swe.learnstruts2.LoginAction2 getAge - " getAge is invoked " 
2018-01-12 16:37:41.742 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsernameAndPassword - " getUsernameAndPassword is in invoked " 

没有age表单，在源Action有getAge{return age+55}和setAge{this.age=age+33},返回页面结果是：age:55
2018-01-12 16:47:33.884 TRACE edu.whu.swe.learnstruts2.LoginAction setUsername - " setUsername is in invoked " 
2018-01-12 16:47:33.933 TRACE edu.whu.swe.learnstruts2.LoginAction validate - " validate is invoked " 
LoginAction is executed
2018-01-12 16:47:33.955 TRACE edu.whu.swe.learnstruts2.LoginAction getAge - " setAge is invoked " 
2018-01-12 16:47:33.955 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
2018-01-12 16:47:33.956 TRACE edu.whu.swe.learnstruts2.LoginAction getUsername - " getUsername is in invoked " 
2018-01-12 16:47:33.956 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:47:33.956 TRACE edu.whu.swe.learnstruts2.LoginAction getUsernameAndPassword - " getUsernameAndPassword is in invoked " 
2018-01-12 16:47:33.957 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsernameAndPassword - " setUsernameAndPassword is in invoked " 
2018-01-12 16:47:33.960 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:47:33.971 TRACE edu.whu.swe.learnstruts2.LoginAction2 validate - " validate is invoked " 
2018-01-12 16:47:34.132 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsername - " getUsername is in invoked " 
2018-01-12 16:47:34.133 TRACE edu.whu.swe.learnstruts2.LoginAction2 getAge - " getAge is invoked " 
2018-01-12 16:47:34.134 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsernameAndPassword - " getUsernameAndPassword is in invoked " 


输入age表单值为666，在源Action有getAge{return age+55}和setAge{this.age=age+33},在目标Action中打印相应的Filed。返回页面结果是：age:22
2018-01-12 17:19:51.730 TRACE edu.whu.swe.learnstruts2.LoginAction setAge - " setAge is invoked " 
2018-01-12 17:19:51.731 TRACE edu.whu.swe.learnstruts2.LoginAction setUsername - " setUsername is in invoked " 
2018-01-12 17:19:51.731 TRACE edu.whu.swe.learnstruts2.LoginAction validate - " validate is invoked " 
LoginAction is executed
2018-01-12 17:19:51.734 TRACE edu.whu.swe.learnstruts2.LoginAction getAge - " setAge is invoked " 
2018-01-12 17:19:51.734 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
setAge:  754
2018-01-12 17:19:51.735 TRACE edu.whu.swe.learnstruts2.LoginAction getUsername - " getUsername is in invoked " 
2018-01-12 17:19:51.736 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 17:19:51.736 TRACE edu.whu.swe.learnstruts2.LoginAction getUsernameAndPassword - " getUsernameAndPassword is in invoked " 
2018-01-12 17:19:51.736 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsernameAndPassword - " setUsernameAndPassword is in invoked " 
2018-01-12 17:19:51.737 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
setAge:  666
2018-01-12 17:19:51.737 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 17:19:51.738 TRACE edu.whu.swe.learnstruts2.LoginAction2 validate - " validate is invoked " 
2018-01-12 17:19:51.741 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsername - " getUsername is in invoked " 
2018-01-12 17:19:51.741 TRACE edu.whu.swe.learnstruts2.LoginAction2 getAge - " getAge is invoked " 
getAge:  666
2018-01-12 17:19:51.742 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsernameAndPassword - " getUsernameAndPassword is in invoked " 



输入age表单值为666，在源Action有getAge{return age+55}和setAge{this.age=age+33},设置setAttribute("age",22);在目标Action中打印相应的Filed。返回页面结果是：age:22
2018-01-12 16:56:50.179 TRACE edu.whu.swe.learnstruts2.LoginAction setAge - " setAge is invoked " 
2018-01-12 16:56:50.195 TRACE edu.whu.swe.learnstruts2.LoginAction setUsername - " setUsername is in invoked " 
2018-01-12 16:56:50.229 TRACE edu.whu.swe.learnstruts2.LoginAction validate - " validate is invoked " 
LoginAction is executed
2018-01-12 16:56:50.249 TRACE edu.whu.swe.learnstruts2.LoginAction getAge - " setAge is invoked " 
2018-01-12 16:56:50.250 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
setAge:  754
2018-01-12 16:56:50.250 TRACE edu.whu.swe.learnstruts2.LoginAction getUsername - " getUsername is in invoked " 
2018-01-12 16:56:50.250 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:56:50.251 TRACE edu.whu.swe.learnstruts2.LoginAction getUsernameAndPassword - " getUsernameAndPassword is in invoked " 
2018-01-12 16:56:50.251 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsernameAndPassword - " setUsernameAndPassword is in invoked " 
2018-01-12 16:56:50.253 TRACE edu.whu.swe.learnstruts2.LoginAction2 setAge - " setAge is invoked " 
setAge:  666
2018-01-12 16:56:50.255 TRACE edu.whu.swe.learnstruts2.LoginAction2 setUsername - " setUsername is in invoked " 
2018-01-12 16:56:50.263 TRACE edu.whu.swe.learnstruts2.LoginAction2 validate - " validate is invoked " 
2018-01-12 16:56:50.414 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsername - " getUsername is in invoked " 
2018-01-12 16:56:50.415 TRACE edu.whu.swe.learnstruts2.LoginAction2 getUsernameAndPassword - " getUsernameAndPassword is in invoked "
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原文地址：https://www.cnblogs.com/JMLiu/p/8277435.html