Struts2中的ModelDriven机制及其运用

所谓ModelDriven，意思是直接把实体类当成页面数据的收集对象。比如，有实体类User如下：

package cn.com.leadfar.struts2.actions;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;    }}

假如要写一个Action，用来添加User。

第一种做法是直接在Action中定义所有需要的属性，然后在JSP中直接用属性名称来提交数据：

UserAction:

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

add_input.jsp:

 <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="添加用户">     </form> <br/>

上述做法不好之处是：如果实体类的属性非常多，那么Action中也要定义相同的属性。

第二种做法是将User对象定义到UserAction中，然后在JSP中通过user属性来给user赋值：

UserAction:

public class UserAction {    private User user;    public String add(){       new UserManager().addUser(user);             return "success";    }    public User getUser() {       return user;    }    public void setUser(User user) {       this.user = user;    }}

add_input.jsp:

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

这种做法不好的地方是：JSP页面上表单域中的命名变得太长

第三种做法是利用ModelDriven机制，让UserAction实现一个ModelDriven接口，同时实现接口中的方法：getModel()。如下所示：

public class UserAction implements ModelDriven{    private User user;    @Override    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;    }}

JSP的代码如下：

 <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/>        <input type="submit" name="submit" value="添加用户">     </form> <br/>

可见，第三种做法是比较好的，Action和JSP写起来都比较简单。