Struts2的学习(3)-ModelDriven接口的应用

1.现在我们有EmployeeAction的Action类如下：

package com.yu.struts2.app;

import java.util.Map;

import org.apache.struts2.interceptor.RequestAware;

public class EmployeeAction implements RequestAware {

private Integer employeeId;

private Dao dao = new Dao();

public String list(){
requestMap.put("emps", dao.getEmployees());
return "list";
}

public String delete(){
dao.delete(employeeId);
return "delete";
}

private String firstName;
private String lastName;
private String email;

public String save(){
Employee emp = new Employee(null, firstName, lastName, email);
dao.save(emp);

return "save";
}

private Map<String, Object> requestMap;

@Override
public void setRequest(Map<String, Object> arg0) {
// TODO Auto-generated method stub
this.requestMap = arg0;
}

public Integer getEmployeeId() {
return employeeId;
}

public void setEmployeeId(Integer employeeId) {
this.employeeId = employeeId;
}

public void setFirstName(String firstName){
this.firstName = firstName;
}

public String getFirstName(){
return this.fristName;
}

public void setLastName(String lastName){
this.lastName = lastName;
}

public String getLastName(){
return this.lastName;
}

public void setEmail(String email){
this.email= email;
}

public String getLastName(){
return this.lastName;
}

}

2.同时，我还编写了一个Employee这个类，如下：

package com.yu.struts2.app;

public class Employee {

private Integer employeeId;
private String firstName;
private String lastName;

private String email;

public Integer getEmployeeId() {
return employeeId;
}

public void setEmployeeId(Integer employeeId) {
this.employeeId = employeeId;
}

public String getFirstName() {
return firstName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

public String getLastName() {
return lastName;
}

public void setLastName(String lastName) {
this.lastName = lastName;
}

public String getEmail() {
return email;
}

public void setEmail(String email) {
this.email = email;
}

public Employee(Integer employeeId, String firstName, String lastName, String email) {
super();
this.employeeId = employeeId;
this.firstName = firstName;
this.lastName = lastName;
this.email = email;
}

public Employee() {
super();
}

}

3.我们可以看出我现在save一个employee， 我在Action类中差不多实现了Employee类的所有成员和方法，我们可以看到Action类太过于繁琐，那么我们可不可以简化一下，把Action中涉及到的Employee类的成员变量和方法去掉，直接将值栈里面的属性值赋给一个Employee对象中，这样的话那么我们要使值栈的第一个对象栈必须是Employee对象，因此ModelDriven接口是处理这种问题解接口。
4.我们可以把EmployeeAction的类改写成：

package com.yu.struts2.app;

import java.util.Map;

import org.apache.struts2.interceptor.RequestAware;

import com.opensymphony.xwork2.ModelDriven;

public class EmployeeAction implements RequestAware ,ModelDriven<Employee>{

private Integer employeeId;

private Dao dao = new Dao();

public String list(){
requestMap.put("emps", dao.getEmployees());
return "list";
}

public String delete(){
dao.delete(employee.getEmployeeId());
return "success";
}

private Employee employee;

public String save(){
// 1.获取请求参数：通过定义对应属性的方式
// 2.调用Dao的save方法
dao.save(employee);

return "success";
}

private Map<String, Object> requestMap;

@Override
public void setRequest(Map<String, Object> arg0) {
// TODO Auto-generated method stub
this.requestMap = arg0;
}

@Override
public Employee getModel() {
// TODO Auto-generated method stub
employee = new Employee();
return employee;
}
}

它的实现很简单，实现ModelDriven这个接口，并且通过getModel()方法得到Employee对象。

5.下面我们来具体分析下这个过程：
(1) 先执行ModelDrivenInterceptor的Intercept方法
代码分析：

public String intercept(ActionInvocation invocation) throws Exception {
// 获取Action对象：Employee对象，此时该Action已经实现了ModelDriven接口
// public class EmployeeAction implements RequestAware ,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()方法返回值压入到值栈的栈顶。实际压入的是EmployeeAction的执行变量
stack.push(model);
}
if (refreshModelBeforeResult) {
invocation.addPreResultListener(new RefreshModelBeforeResult(modelDriven, model));
}
}
return invocation.invoke();
}

(2).执行ParametersInterceptor 的intercept方法：把请求参数的赋值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 Employee对象到值栈的栈顶，但当前Action的employee成员变量却是null

public Employee getModel() {
//employee = new Employee();
return new Employee();
}