JSF2:如何在部署时启动服务 [英] JSF2: How to initiate services at deployment

问题描述

对于大学项目，我正在使用JSF开发一个Web应用程序.我的工作是做前端.一个同伴应该做后端的东西.这两部分均设计为实用的应用程序.两者都通过RMI进行通信.我想在部署时打开一次连接.

For university project I am developing a webapplication with JSF. My excercise is to do the frontend. A fellow studend is supposed to do backend stuff. Both parts are designed to be seerate applications. Both communicate through RMI. I want to open the connection once at deployment.

我现在是要建立连接的时候了.我尝试使用@ApplicationScoped ManagedBean做到这一点:

I am at the point to settle up the connection now. I tried to do that with a @ApplicationScoped ManagedBean:

//Constructor of ApplicationScoped ManagedBean  
public Communication() {
    this.connect();
}

有可能吗?我试过了，但是似乎没有调用managedBean.

Is that way possible? I tried it but the managedBean seems not to be called..

您能提出最佳实践建议吗?

Can you advice a Best Practice?

@Brian:不幸的是，我根本不使用EJB -.-

@Brian: Unfortunately I don't use EJB at all -.-

@BalusC的底池: 我创建了一个communicationbean:

@BalusC's pot: I created a communicationbean:

@ManagedBean(name="communication")
@ApplicationScoped
public class Communication {

    public static FrontendCommInterface server;

    public Communication() {
        this.connect();
    }

然后我创建了LoginBean:

Then I created the LoginBean:

@ManagedBean
@ViewScoped
public class Login {

@ManagedProperty(value="#{communication}")
private Communication communicationBean;

public FrontendCommInterface server;

private String username;
private String password;

public Login() {
    server = communicationBean.getConnection();
}

public String login(){
    HttpSession session = (HttpSession) FacesContext.getCurrentInstance().getExternalContext().getSession(true);
    String sessionId = session.getId();

    try {
        server.login(getUsername(), getPassword(), sessionId);
        return "start.xhtml";

    } catch (RemoteException e) {
        e.printStackTrace();
        FacesContext.getCurrentInstance().addMessage(null, new FacesMessage(FacesMessage.SEVERITY_ERROR,"Anmeldung nicht erfolgreich: ", getUsername()+", "+getPassword()+", "+sessionId));
        return "login.xhtml";
    }
}

但不幸的是，它引发了异常:

But unfortunately it throws exceptions:

com.sun.faces.mgbean.ManagedBeanCreationException: Klasse org.dhbw.stg.wwi2008c.mopro.ui.managedBeans.Login can not be instanciated.

java.lang.NullPointerException
    org.dhbw.stg.wwi2008c.mopro.ui.managedBeans.Login.<init>(Login.java:28)

调试之后，我发现我的ManagedProperty为Null！尚未创建！怎么做?我认为通过ManagedProperty引用会创建它-.-

After debuging I found out that my ManagedProperty is Null ! It hasn't been created! How to do that? I thought referencing via managedproperty would create it -.-

推荐答案

仅当EL #{managedBeanName}引用托管bean时才自动创建托管bean，这可以通过按原样访问view或通过作为另一个bean的托管属性注入，或由例如EL手动解析Application#evaluateExpressionGet().

The managed bean is only auto-created whenever it's been referenced by EL #{managedBeanName}, which can happen by either accessing as-is in view, or by being injected as managed property of another bean, or being manually EL-resolved by e.g. Application#evaluateExpressionGet().

在您的特定情况下，您实际上想在webapp启动期间初始化一些内容.您宁愿为此使用 ServletContextListener .

In your particular case, you actually want to intialize some stuff during webapp's startup. You rather want to use ServletContextListener for this.

@WebListener
public class Config implements ServletContextListener {

    public void contextInitialized(ServletContextEvent event) {
        // Do stuff during webapp's startup.
    }

    public void contextDestroyed(ServletContextEvent event) {
        // Do stuff during webapp's shutdown.
    }

}

您甚至可以在必要时在此预先创建一个应用程序范围的托管Bean(如果您的意图是能够通过@ManagedProperty从其他Bean访问它).

You could even pre-create an application scoped managed bean there whenever necessary (if your intent is to be able to access it from other beans by @ManagedProperty).

    public void contextInitialized(ServletContextEvent event) {
        event.getServletContext().setAttribute("bean", new Bean());
    }

JSF将应用程序范围的bean作为ServletContext的属性存储，并且JSF不会自动创建另一个bean，因此JSF将使用与上面的代码示例创建的一个bean相同的对象.也是

JSF stores application scoped beans as an attribute of the ServletContext and JSF won't auto-create another one when one is already present, so the one and the same as created by the above code example will be used by JSF as well.

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