Java 简单的单例EJB示例
我正在学习EJB,并使用GlassFish 4编写了一个示例程序,但由于某些原因,它不起作用 index.jsp:Java 简单的单例EJB示例,java,ejb,Java,Ejb,我正在学习EJB,并使用GlassFish 4编写了一个示例程序,但由于某些原因,它不起作用 index.jsp: <%@page contentType="text/html" pageEncoding="UTF-8"%> <%@ page import="javax.ejb.EJB" %> <%@ page import="ejbtest.utility.Utility" %> <%@ page import="ejbtest.action.*" %
<%@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>
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;
}
}
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();
}
}
触发器1.java:
<%@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>
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;
}
}
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();
}
}
不需要的输出:
<%@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>
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;
}
}
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();
}
}
计数:1
空指针捕捉
我认为您只能在其他
会话bean
或消息驱动bean
中注入EJB
。在您的代码中,您尝试将它们注入到简单的java类中。您可以使用JNDI查找
在java类中引用它们
如果类Trigger1
和Trigger2
与Utility
Bean不在同一(JavaEE
)应用程序中,那么您需要Remote
访问,因此需要一个接口视图。然后,您可以按如下方式访问Singleton
Bean:
如果您的
Trigger1
和Trigger2
类与您的实用工具
Bean处于相同的应用程序中,那么您已经提供的本地无接口视图就足够了。您可以像这样通过Injection
访问Singleton
Bean,但必须使类会话
Bean(最好是无状态的)。然后您应该再次通过JNDI查找
从主方法访问它们 首先,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,将忽略所有EJB注释。您需要像glassfish或JBoss这样的应用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();
}
}
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;
}
}
Utility.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();
}
}
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;
}
}
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>
EJB测试
你能告诉我什么样的代码需要修改吗?因为我对所有这些术语都还不太熟悉,所以我在Tomcat 7和GlassFish 4中尝试将其作为一个JSP脚本而不是一个主类,但我得到了同样的东西…show scriplet code。如果您的操作与此处的new Trigger1()相同,那么它是错误的。由您自己创建的对象在EJB容器外部创建,并忽略EJB注释。您的Trigger1对象必须由EJB容器创建。正如我所说的,您使用新操作符来获取EJB。这是错误的,您应该使用初始上下文为您的EJB获取链接。比如:InitialContext ic=newinitialcontext();实用工具=(实用工具)ic.lookup(“实用工具”);如果我使用的是EJB3.2,我就不能使用注释来进行查找吗?我以为这就是@Local
、@EJB
和@Remote
等的目的?看看我的编辑。您可以在一个EJB注入其他EJB的过程中使用注释。但如果在jsp页面中使用EJB,则必须使用InitialContext