jsf-2 - EJB 方法不是从构造函数调用

Question

我创建了一个ejb

@Stateless
@LocalBean   
public class BasitBean {

    public String helloBasit() {

        return "Basit";

    } //end of helloBasit()

} //end of class BasitBean

我是从 JSF 调用它的，比如

<h:body>

    <h:outputLabel value="#{helloBasit.callBasit()}" />

</h:body>

@ManagedBean
@SessionScoped
public class HelloBasit {

    @EJB
    private BasitBean basitBean;

    /** Creates a new instance of HelloBasit */
    public HelloBasit() {         

    }

    public String callBasit() {

        return basitBean.helloBasit();

    } //end of callBasit()

} //end of class HelloBasit

这段代码运行良好。但是当我像这样更改代码时

<h:body>
    <h:outputLabel value="#{helloBasit.label}" />        
</h:body>

@ManagedBean
@SessionScoped
public class HelloBasit {

    @EJB
    private BasitBean basitBean;
    String label;

    /** Creates a new instance of HelloBasit */
    public HelloBasit() {

        System.out.println();
        String label = basitBean.helloBasit();
        System.out.println(label);

    }

    public BasitBean getBasitBean() {
        return basitBean;
    }

    public void setBasitBean(BasitBean basitBean) {
        this.basitBean = basitBean;
    }

    public String getLabel() {
        return label;
    }

    public void setLabel(String label) {
        this.label = label;
    }

} //end of class HelloBasit

然后我得到异常

SEVERE: Error Rendering View[/index.xhtml]
com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: pk.mazars.basitMahmood.HelloBasit.
 at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:193)
 at com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:102)
 ......

为什么我会收到此异常？流程应该是我理解的是当我的页面遇到 #{helloBasit.label} 然后我的构造函数被调用，实例变量被初始化，将 bean 实例注入(inject) basitBean，然后 bean 方法应该调用.但是在这种情况下我在 bean 实例中得到 null 为什么？为什么以前的代码可以工作而不能？我如何从构造函数中调用 bean？

谢谢。

Answer 1

尝试将构造函数的内容移动到后构造函数中......

像这样

@PostConstruct
private void init() {
    System.out.println();
    String label = basitBean.helloBasit();
    System.out.println(label);
}

因为 ejb bean 应该只在托管 bean 启动后注入(inject)

@PostConstruct 在构造函数之后运行(之后托管 bean 本身由 JSF 创建)，然后才将 EJB 注入(inject)到 bean 中并可以访问...