Struts2中的ModelDriven運用

一、在什麼情況下需要使用ModelDriven

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比如有以下User實體類

public class User {
    private int id;
    private String username;
    private String password;
    private int age;
    private String address;
    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 String getAddress() {
       return address;
    }
    public void setAddress(String address) {
       this.address = address;
    }
    public int getId() {
       return id;
    }
    public void setId(int id) {
       this.id = id;
    }
} 

假如現在要實現添加User的功能，剛學strust2的時候我們都是現在action中定義相應屬性的get、set方法以設置跟獲取相應的值。但是這無疑十分麻煩，當屬性十分多的時候，顯得代碼十分臃腫。
如下爲UserAction

Class UserAction{
    private int id;
    private String username;
    private String password;
    private int age;
    private String address;
    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 String getAddress() {
       return address;
    }
    public void setAddress(String address) {
       this.address = address;
    }
    public int getId() {
       return id;
    }
    public void setId(int id) {
       this.id = id;
    }

    public String add(){
        User user = new User();
        user.setId(id);
        user.setUsername(username);
        user.setPassword(password);
        user.setAge(age);
        user.setAddress(address);

        new UserManager().addUser(user);

        return "success";
    }
}

增加User用戶的add.jsp頁面

 <form action="test/user.action" method="post">
     <input type="hidden" name="method:add">
     username:<input type="text" name="username"> <br/>
     password:<input type="text" name="password"> <br/>
     age:<input type="text" name="age"> <br/>
     address:<input type="text" name="address"> <br/>
     <input type="submit" name="submit" value="添加用戶">
 </form>

可以看到，在action類裏面又要重複寫一次在user實體類裏面的get、set方法。

二、如何使用ModelDriven來減少action中不必要的get、set方法

public class UserAction implements ModelDriven{

    private User user;

    public Object getModel() {
       if(user == null){
           user = new User();
       }
       return user;
    }

    public String add(){

       new UserManager().addUser(user);

       return "success";
    }

    public User getUser() {
       return user;
    }

    public void setUser(User user) {
       this.user = user;
    }
}

這樣就可以減少很多重複的代碼