Spring UI Scope

Spring UI Scope

The add-on has defined custom Spring scope: UI.

Please analyze sample application 'Simple Bank' to see how scope UI is used to create Spring powered Vaadin application in Model-View-Presenter architecture

Keep the following rules:

1. Model (pojo) usually is singleton Spring bean
2. Presenter (pojo) is UI-scope proxy Spring bean
3. View (Vaadin component) is UI-scope Spring bean

Restrictions are cause by circular dependency between View and Presenter. Spring allows that only if one party is a proxy. If View is a proxy, Vaadin framework fails. Possible reason is that the framework use protected or package methods, which are not handled by proxy; only public methods are handled. Therefore, View must be UI-scope normal class and Presenter must be UI-scope proxy bean.

Sample code

<dependency>
    <groupId>com.cybercom</groupId>
    <artifactId>spring-ui-scope</artifactId>
    <version>0.0.2</version>
</dependency>

@Configuration
public class Conf {
	
	@Bean static UIScope uiScope() {
		return new UIScope();
	}
}

/**
 * Never define View bean as Spring Proxy. 
 * That means circular dependency between 2 views is not possible with scope UI
 */
@Component
@Scope(value = "ui")
public class AccountView extends HorizontalLayout {

	private Table accountTable;
	
	private Table operationTable;

	private BeanItemContainer<Account> accounts = new BeanItemContainer<Account>(Account.class);

	private BeanItemContainer<Operation> operations = new BeanItemContainer<Operation>(Operation.class);

	@Autowired
	private AccountPresenter presenter;
	
	/**
	 * @see TopView#construct()
	 */
	@PostConstruct
	private void construct() {
		accountTable = new Table("Accounts - click entry for details", accounts);
		accountTable.setImmediate(true);
		accountTable.setSelectable(true);
		addComponent(accountTable);

		accountTable.addValueChangeListener(new Property.ValueChangeListener() {

			@Override
			public void valueChange(ValueChangeEvent event) {
				presenter.accountClicked((Account)accountTable.getValue());
			}
		});
		
		operationTable = new Table("Operations", operations);
		addComponent(operationTable);

	}

	public void attach() {
		/*
		 * There is a problem where view initialization;
		 * 1. Presenter has logic to initialize View
		 * 2. But Presenter cannot be called in @PostConstruct (circular reference)
		 * 
		 * I decided to defer initialization to method attach()
		 */
		presenter.initAccounts();

		super.attach();
	}

	public BeanItemContainer<Account> getAccounts() {
		return accounts;
	}
	
	public BeanItemContainer<Operation> getOperations() {
		return operations;
	}
}

/**
 * There is a circular reference between View and Presenter. It is typical
 * for MVP, but Spring guys don't like it. Only singleton beans may have circular reference.
 * Then, one side of relation must be proxy. View cannot be proxy because Vaadin is really confused.
 * Simply, Presenter must be the proxy.
 * 
 */
@Component
@Scope(value="ui", proxyMode=ScopedProxyMode.TARGET_CLASS)
public class AccountPresenter {
	
	@Autowired
	private AccountView view;
	
	@Autowired
	private AccountModel model;
	

	public void initAccounts() {
		List<Account> accounts = model.getAccounts();
		view.getAccounts().addAll(accounts);
	}


	public void accountClicked(Account account) {
		if (account == null) {
			view.getOperations().removeAllItems();
			return;
		}
		List<Operation> operations = model.getOperations(account);
		view.getOperations().removeAllItems();
		view.getOperations().addAll(operations);
	}

}

Links

• Example Source code
• Source Code

Compatibility