Struts2中的ModelDriven接口

若没有实现ModelDriven的接口，Controll的代码会比较冗余，不能实现Controll和Model代码的分离

下面是没有实现ModelDriven接口的SuggestAction

 package dayday.controll;

 import com.opensymphony.xwork2.ActionSupport;
 import com.opensymphony.xwork2.ModelDriven;
 import dayday.model.Product;
 import dayday.model.Suggest;
 import dayday.service.AddSuggest;

 /**
  * Created by I am master on 2017/2/22.
  */
 public class SuggestAction extends ActionSupport{
     //保存对象的信息
     private Suggest suggest;
     private AddSuggest addSuggest;

     private String sugName;
     private String sugEmail;
     private String sugPhone;
     private String sugContent;

     public String getSugName() {
         return sugName;
     }

     public void setSugName(String sugName) {
         this.sugName = sugName;
     }

     public String getSugEmail() {
         return sugEmail;
     }

     public void setSugEmail(String sugEmail) {
         this.sugEmail = sugEmail;
     }

     public String getSugPhone() {
         return sugPhone;
     }

     public void setSugPhone(String sugPhone) {
         this.sugPhone = sugPhone;
     }

     public String getSugContent() {
         return sugContent;
     }

     public void setSugContent(String sugContent) {
         this.sugContent = sugContent;
     }

     @Override
     public String execute()throws Exception{
         suggest.setSugContent(getSugContent());
         suggest.setSugEmail(getSugEmail());
         suggest.setSugName(getSugName());
         suggest.setSugPhone(getSugPhone());
         addSuggest.insertSuggest(suggest);
         return SUCCESS;
     }
 }

实现了ModelDriven接口的SuggestAction接口以后的代码

 package dayday.controll;

 import com.opensymphony.xwork2.ActionSupport;
 import com.opensymphony.xwork2.ModelDriven;
 import dayday.model.Product;
 import dayday.model.Suggest;
 import dayday.service.AddSuggest;

 /**
  * Created by I am master on 2017/2/22.
  */
 public class SuggestAction extends ActionSupport implements ModelDriven<Suggest>{
     //保存对象的信息
     private Suggest suggest;
     private AddSuggest addSuggest;

     @Override
     public String execute()throws Exception{
         addSuggest.insertSuggest(suggest);
         return SUCCESS;
     }

     @Override
     public Suggest getModel() {
         suggest=new Suggest();
         return suggest;
     }
 }

明显代码量减少了很多，实现了分离

Action实现ModelDriven接口运行的原理

 1). 先会执行 ModelDrivenInterceptor 的 intercept 方法. 

     public String intercept(ActionInvocation invocation) throws Exception {
         //获取 Action 对象: SuggestAction 对象, 此时该 Action 已经实现了 ModelDriven 接口
         //public class SuggestAction extends ActionSupport, implements ModelDriven<Employee>
         Object action = invocation.getAction();

         //判断 action 是否是 ModelDriven 的实例
         if (action instanceof ModelDriven) {
             //强制转换为 ModelDriven 类型
             ModelDriven modelDriven = (ModelDriven) action;
             //获取值栈
             ValueStack stack = invocation.getStack();
             //调用 ModelDriven 接口的 getModel() 方法
             //即调用 EmployeeAction 的 getModel() 方法
             /*
             public Employee getModel() {
                 employee = new Employee();
                 return employee;
             }
             */
             Object model = modelDriven.getModel();
             if (model !=  null) {
                 //把 getModel() 方法的返回值压入到值栈的栈顶. 实际压入的是 EmployeeAction 的 employee 成员变量
                 stack.push(model);
             }
             if (refreshModelBeforeResult) {
                 invocation.addPreResultListener(new RefreshModelBeforeResult(modelDriven, model));
             }
         }
         return invocation.invoke();
     }

 2). 执行 ParametersInterceptor 的 intercept 方法: 把请求参数的值赋给栈顶对象对应的属性. 若栈顶对象没有对应的属性, 则查询
 值栈中下一个对象对应的属性...

 3). 注意: getModel 方法不能提供以下实现. 的确会返回一个 Suggest 对象到值栈的栈顶. 但当前 Action
 的 suggest 成员变量却是 null. 

 public Suggest getModel() {
     return new Suggest();
 }