NullPointerException error when using ModelDriven

Question

I have two classes as following

Address
  int ID
  int unit
  String street 

User 
    int ID 
    String Name
    Address address

my user class

public class user{
    .....
    private Address address;
     ...getters setters...
}

As shown above User class has an object of Address class in it. My code is expected to receive the values of a form and show them on console.

But when I try to access the unit attribute of address class it shows the following error.

"SEVERE: Exception occurred during processing request: null java.lang.NullPointerException"

my controller

@Action
class myclass implements ModelDriven{

   private User user = new User();

   public Register(){
       System.out.println("User's Unit" + user.getAddress().getUnit()); // error is on this line
   }
     @Override
    public Object getModel() {
       return user;
    }

jsp file

<s:form action="Register">
             <s:textfield name="name" label="Name"/>
             <s:textfield name="unit" label="Unit"/>
             <s:textfield name="block" label="Block"/>
</s:form>

where exactly do you want to use your OTHER class attributes? — Rahul, Feb 13 '13 at 04:08
@R.J I need to have access to them in my controller to send them to my model to be saved on database. — Daniel Morgan, Feb 13 '13 at 04:09
**System.out.println("User's Unit" + user.getAddress().getUnit());** - you've already used it. Your question is still too vague. — Rahul, Feb 13 '13 at 04:15
@R.J, I used that as shown on question but it runs into error, I have also updated the question — Daniel Morgan, Feb 13 '13 at 04:19

score 2 · Accepted Answer · edited May 03 '14 at 22:10

2

do the following mate

<s:textfield name="address.unit" label="Unit"/>

edited May 03 '14 at 22:10

BenMorel

34,448
50
182
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answered Feb 13 '13 at 04:35

CodeHunter · Answer 2 · 2013-02-13T06:56:26.777

try this action class this will definitly work

public class myclass extends ActionSupport implements ModelDriven<User>, Preparable{

    private User user = new User();

@Override
public void prepare() throws Exception {
    user=new User();
}

@Override
public User getModel() {
    return user;
}
public Register(){
   System.out.println("User's Unit" + user.getAddress().getUnit()); 
   }
}

and change the jsp

<s:textfield name="address.unit" label="Unit"/>

for setting only unit property

score 1 · Answer 3 · answered Feb 13 '13 at 05:17

 <s:textfield name="name" label="Name"/>

Here struts2 will search for name="name" property in the related DTO's in your respective action, but value-stack will failed to find the property named "name" in your action, because you have created a different bean class Address which is having member "name". So you have to tell your form-element that "name" instance resides in different POJO i.e. Adderess . So make changes like this:

<s:textfield name="address.name" label="name"/>

score 0 · Answer 4 · answered Feb 13 '13 at 04:32

0

the problem as I see it is, you've not newd address object

address = new Address(); in the constructor of User class.

answered Feb 13 '13 at 04:32

Aniket Inge

25,375
5
50
78

score 0 · Answer 5 · answered Feb 13 '13 at 04:34

Looks like when you created the user object using "private User user = new User()" the address object of the user is not initialized. As user.getAddress() is null, when you try to invoke user.getAddress().getUnit() it will result in null pointer exception

NullPointerException error when using ModelDriven

5 Answers5