简单的Singleton EJB示例

Question

简单的Singleton EJB示例

我正在学习EJB，并且已经使用GlassFish 4编写了一个示例程序，但是由于某种原因它无法正常工作。

index.jsp：

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@ page import="javax.ejb.EJB" %>
<%@ page import="ejbtest.utility.Utility" %>
<%@ page import="ejbtest.action.*" %>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>EJB Test</title>
    </head>
    <body>
        <%
            try {
                Utility utility = new Utility();
                out.println("count: " + utility.getCount() + "<br/><br/>");
                Trigger1 trigger1 = new Trigger1();
                out.println("trigger1 count: " + trigger1.getTriggerCount());
            } catch (NullPointerException npe) {
                out.println("Nullpointer caught");
            }
        %>
    </body>
</html>

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Utility.java：

package ejbtest.utility;

import javax.ejb.Singleton;
import javax.ejb.Startup;

@Startup
@Singleton
public class Utility {

    int count;

    public Utility() throws NullPointerException {
        count = 0;
        count++;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }
}

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Trigger1.java：

package ejbtest.action;

import ejbtest.utility.Utility;
import javax.faces.bean.ApplicationScoped;
import javax.inject.Inject;

@ApplicationScoped
public class Trigger1 {

    @Inject
    Utility utility;

    public Integer getTriggerCount() {
        return utility.getCount();
    }

}

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不良输出：

数：1

空指针被抓住

Answer 1

Fir*_*rks 5

首先，您要在标准JVM中启动EJB。但是EJB只能存在于EJB容器中。当您仅使用main方法启动应用程序时，所有EJB注释都将被忽略。您需要像glassfish或JBoss这样的应用程序服务器来测试您的应用程序。
这里是您的改进示例：

Trigger1.java

package ejbtest.action;

import javax.ejb.EJB;
import javax.ejb.Stateless;

import ejbtest.utility.Utility;

@Stateless
public class Trigger1 {

    @EJB
    private Utility utility;

    public Integer getTriggerCount() {
        return utility.getCount();
    }
}

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Utility.java

package ejbtest.utility;

import javax.annotation.PostConstruct;
import javax.ejb.Singleton;

@Singleton
public class Utility {
    int count = 0;

    @PostConstruct
    public void init() {
        count++;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }
}

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index.jsp

<%@page import="ejbtest.action.Trigger1"%>
<%@page import="ejbtest.utility.Utility"%>
<%@page import="javax.naming.InitialContext"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>EJB Test</title>
    </head>
    <body>
    <%
        InitialContext ic = new InitialContext();
        Utility utility = (Utility) ic.lookup("java:module/Utility");
        out.println("count: " + utility.getCount() + "<br/><br/>");
        Trigger1 trigger1 = (Trigger1) ic.lookup("java:module/Trigger1");
        out.println("trigger1 count: " + trigger1.getTriggerCount());
    %>
    </body>
</html>

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