Question

每当我尝试将会话范围的bean注入到我的视图范围的bean中时，我在调用所述bean时会得到NullPointerException。此问题与auto -instantiate a session bean?

直接相关

这是我到目前为止所尝试的内容：

faces-config.xml中

<managed-bean>
    <managed-bean-name>sessionBean</managed-bean-name>
    <managed-bean-class>com.example.SessionBean</managed-bean-class>
    <managed-bean-scope>session</managed-bean-scope>
</managed-bean>
<managed-bean>
    <managed-bean-name>viewBean</managed-bean-name>
    <managed-bean-class>com.example.ViewBean</managed-bean-class>
    <managed-bean-scope>view</managed-bean-scope>
    <managed-property>
        <property-name>sessionBean</property-name>
        <property-class>com.example.SessionBean</property-class>
        <value>#{sessionMBean}</value>
    </managed-property>
</managed-bean>

SessionBean.java：

package com.example;

public class SessionBean {

    public SessionBean() {
        System.out.println("Session is instantiated.");
    }

    public void sayHello() {
        System.out.println("Hello from session");
    }
}

ViewBean.java：

package com.example;

public class ViewBean {

    private SessionBean sessionBean;

    private String text = "Look at me!";

    public ViewBean() {
        System.out.println("View bean is instantiated.");

        sessionBean.sayHello();
    }

    public SessionBean getSessionBean() {
        return sessionBean;
    }

    public void setSessionBean(SessionBean sessionBean) {
        this.sessionBean = sessionBean;
    }

    public String getText() {
        return text;
    }
}

和index.xhtml的相关内容：

<f:view>
    <h:outputText value="#{viewBean.text}"/>
</f:view>

这就是我得到的：

com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: com.example.ViewBean.
...
Caused by: java.lang.NullPointerException
    at com.example.ViewBean.(ViewBean.java:12)

这在weblogic-10.3.6上运行（或者说不运行），并将jsf-2-0.war作为库部署。

我在这里做错了什么？我希望这不是容器错误......

Answer 1

您无法访问@SessionScoped构造函数中的@ViewScoped bean。 @SessionScoped bean将在调用@ViewScoped bean的构造函数之后设置。在某种 init 方法中使用@PostConstruct注释来访问@SessionScoped bean。

public ViewBean() {
  System.out.println("Constructor viewbean");
}

@PostConstruct
public void init() {
  sessionBean.sayHello();
}

进一步的链接：
Why use @PostConstruct?
Spring Injection - access to the injected object within a constructor

从视图范围的bean自动实例化会话范围的bean

1 个答案: