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:

<form action="test/user.action" method="post">
<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