CODEWITHSUNDEEP
javajspstruts2javabeansinterceptorstack
ponder275
ponder275

Reputation: 935

What is the correct way to initialize fields of Action classes in Struts 2?

I have a class which I am using to store data that I retrieve from a database which has objects as fields.

I want to initialize the objects when the class is instantiated to avoid null pointer problems.

I thought I read somewhere that it should not initialize the fields in the field declaration because it may cause problems for Struts (but I can't find the statement now), so I am initializing the fields in the constructor.

My question is:

Does it matter which way you do it? Or should you not do it at all and only put in the new objects after you instantiate the class? In other words should I define my class like this:

public class MenuView implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

private ProjectInfo projectInfo;
private PartyInfo partyInfo;
private RequestTableInfo requestTableInfo;
private PartyRequestInfo partyRequestInfo;

public MenuView(){
    projectInfo = new ProjectInfo();
    partyInfo = new PartyInfo();
    requestTableInfo = new RequestTableInfo();
    partyRequestInfo = new PartyRequestInfo();
}

followed by getters and setters or like this.

public class MenuView implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

private ProjectInfo projectInfo = new ProjectInfo();
private PartyInfo partyInfo = new PartyInfo();
private RequestTableInfo requestTableInfo = new RequestTableInfo();
private PartyRequestInfo partyRequestInfo = new PartyRequestInfo();

public MenuView(){  }

followed by getters and setters or like this:

public class MenuView implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

private ProjectInfo projectInfo;
private PartyInfo partyInfo;
private RequestTableInfo requestTableInfo;
private PartyRequestInfo partyRequestInfo;

public MenuView(){}

followed by getters and setters and then instantiate it like this:

MenuView menu = new MenuView();
menu.setProjectInfo(new ProjectInfo);

Upvotes: 1

Views: 1281

Answers (3)

Phil
Phil

Reputation: 607

Any of the methods above would work but this would be best. The whole point of initializing a class is to avoid null referenced of course and initialize them with preferred values as shown below.

Adding getters and setters would work just fine from there

public class MenuView implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

private ProjectInfo projectInfo;
private PartyInfo partyInfo;
private RequestTableInfo requestTableInfo;
private PartyRequestInfo partyRequestInfo;

public MenuView(int a, int b, int c, int d){
    projectInfo = new ProjectInfo(a);
    partyInfo = new PartyInfo(b);
    requestTableInfo = new RequestTableInfo(c);
    partyRequestInfo = new PartyRequestInfo(d);
}

Upvotes: 2

Roman C
Roman C

Reputation: 1

It doesn't matter for Struts2, only sufficient that a ModelDriven object you should create yourself (if you are using ModelDriven interface).

The framework will create the objects if they are null when the form is submitted. This option is enabled by default. The magic is performed by the params interceptor which is using OGNL under hoods to populate the model from parameters passed to the action.

While this interceptor is being invoked, a flag (ReflectionContextState#CREATE_NULL_OBJECTS) is turned on to ensure that any null reference is automatically created - if possible. See the type conversion documentation and the InstantiatingNullHandler javadocs for more information.

More or less this feature is documented under com.opensymphony.xwork2.conversion.NullHandler.

The beans should comply a JavaBeans spec., so they could be instantiated by the Struts2 framework (if you want to learn more about JavaBeans, see this post What is a JavaBean exactly).

Upvotes: 0

Andrea Ligios
Andrea Ligios

Reputation: 50261

I read somewhere that you should not initialize the fields in the field declaration because that may cause problems for Struts (but I can't find the statement now)

No, not that I know

so I am initializing the fields in the constructor.

You can, but you're not forced to. I never use constructors on actions (I almost never use constructors at all, since I'm using Java EE 6+ and CDI, and in constructors the @Injected objects have not been injected yet - I use a @PostConstruct method instead, when necessary), but that's up to you, it's not a rule.

My question is does it matter which way you do it?

No

Or should you not do it at all and only put in the new objects after you instantiate the class?

Struts2 will handle the nulls for you in the JSP. The only NullPointerExceptions you must handle are on the Java side, so just check for null, or instantiate the objects in the declaration, and don't worry about it anymore.

Just remember that Struts2 will need a no-arg constructor to instantiate beans with JSP values.

Upvotes: 1

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