利用JBOSS+MyEclipse完成一个简单的EJB示例
目标：
1、编写一个简单的无状态会话Bean，传入一个字符串参数，返回字符串Hello + 字符串参数。
2、通过JSP页面上输入一个字符串，提交到Servlet，并调用EJB，最后在一个页面上输出处理后的字符串。
工具：
JBOSS 4.2GA + Eclipse 3.2.2 +MyEclipse 5.5GA + JDK 1.6
首先需要搭建好各种环境，这一步比较简单，就不再赘述。唯一需要注意的是在启动JBOSS服务器时可能会出现一些问题。如端口号被占用而导致服务器无法启动。如果出现这个问题可以在%JBOSS%/server/default/deploy/jboss-web.deployer/目录下找到server.xml文件，修改<Connector port="8080" address="${jboss.bind.address}"
maxThreads="250" maxHttpHeaderSize="8192"
emptySessionPath="true" protocol="HTTP/1.1"
enableLookups="false" redirectPort="8443" acceptCount="100"
connectionTimeout="20000" disableUploadTimeout="true" />
中的port属性，然后再重新启动服务器。默认端口是8080。
JBOSS自带了TOMCAT 5.X，当然也可以使用另外的Web服务器，不过后面的程序会稍微有些改动。
环境搭建完成后就需要编写EJB代码。一个EJB至少需要3个类，即Home接口、远程接口、实现类。新建一个EJB Project，项目名为：MyFirstEJB.
1、创建Home接口---HelloHome.java
package com.lovo.interfaces;
public interface HelloHome extends javax.ejb.EJBHome {
public com.lovo.interfaces.Hello create() throws javax.ejb.CreateException,
java.rmi.RemoteException;
}
2、创建远程接口---Hello.java
package com.lovo.interfaces;
public interface Hello extends javax.ejb.EJBObject {
public String sayHello(String message) throws java.rmi.RemoteException;
}
3、创建实现类---HelloBean.java
package com.lovo.ejb;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.EJBException;
import javax.ejb.SessionBean;
import javax.ejb.SessionContext;
public class HelloBean implements SessionBean {
private SessionContext context;
public HelloBean() {}
public void ejbActivate() throws EJBException, RemoteException {}
public void ejbPassivate() throws EJBException, RemoteException {}
public void ejbRemove() throws EJBException, RemoteException {}
public void ejbCreate() throws CreateException {}
public void setSessionContext(SessionContext newContext)
throws EJBException {
this.context = newContext;
}
public String sayHello(String message){
if(message == null)
message = "";
message = "Hello " + message + "!";
return message;
}
}
其中方法sayHello就是我们需要实现的业务。
类建好之后，接下来就需要配置相关的xml文件。在该项目下的META-INF里新建两个xml文件ejb-jar.xml和jboss.xml。具体配置如下：
ejb-jar.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb-jar_2_0.dtd">
<ejb-jar>
<description>
<![CDATA[No Description.]]>
</description>
<display-name>Generated by XDoclet</display-name>
<enterprise-beans>
<session>
<description>
<![CDATA[Description for Hello]]>
</description>
<display-name>Name for Hello</display-name>
<ejb-name>Hello</ejb-name>
<home>com.lovo.interfaces.HelloHome</home>
<remote>com.lovo.interfaces.Hello</remote>
<ejb-class>com.lovo.ejb.HelloBean</ejb-class>
<session-type>Stateless</session-type>
<transaction-type>Container</transaction-type>
</session>
</enterprise-beans>
<assembly-descriptor>
</assembly-descriptor>
</ejb-jar>
jboss.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jboss PUBLIC "-//JBoss//DTD JBOSS 2.4//EN" "http://www.jboss.org/j2ee/dtd/jboss_2_4.dtd">
<jboss>
<enterprise-beans>
<session>
<ejb-name>Hello</ejb-name>
<jndi-name>ejb/Hello</jndi-name>
</session>
</enterprise-beans>
<resource-managers>
</resource-managers>
</jboss>
使用XDoclet来自动生成这些文件还是很方便的，只是同时会生成一些多余的类和代码，需要手动去删除他们。
到这里一个简单的无状态会话Bean就完成了，下面就是将他们部署到Jboss下面。可以将项目打包成jar文件，然后放在
%JBOSS%/server/default/deploy/目录下，这样就算部署完成。还可以使用MyEclipse来帮你进行部署。如果控制台上出现：
01:59:48,640 INFO [EjbModule] Deploying Hello
01:59:48,703 INFO [ProxyFactory] Bound EJB Home 'Hello' to jndi 'ejb/Hello'
01:59:48,703 INFO [EJBDeployer] Deployed: file:/%jboss%/server/default/deploy/MyFirstEJB.jar/
就表示部署成功。下面我们就可以编写客户端程序来调用该EJB。
新建一个Web项目，项目名为testEJB，里面包含两个jsp文件和一个servlet。
EJBServlet.java
package com.lovo.servlet;
import java.io.IOException;
import javax.ejb.CreateException;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.lovo.interfaces.Hello;
import com.lovo.interfaces.HelloHome;
public class EJBServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("gb2312");
String info = request.getParameter("info");
InitialContext context = null;
Hello hello = null;
try
{
context = new InitialContext();
HelloHome home = (HelloHome)context.lookup("ejb/Hello");
hello = home.create();
}
catch (NamingException e)
{
e.printStackTrace();
}
catch (CreateException e)
{
e.printStackTrace();
}
info = hello.sayHello(info);
request.setAttribute("info", info);
request.getRequestDispatcher("message.jsp").forward(request, response);
}
}
从jsp页面上获得表单中的字符串，然后将这个字符串传递到EJB的会话Bean中进行处理。最后将返回的字符串显示在另外一个JSP页面上。
index.jsp
<%@ page language="java" isELIgnored="false" pageEncoding="gb2312"%>
<html>
<head>
<title>EJB</title>
</head>
<body>
<form action="servlet" method="post">
<input type="text" name="info" />
<input type="submit" value="提交">
</form>
</body>
</html>
message.jsp
<%@ page language="java" isELIgnored="false" pageEncoding="utf-8"%>
<html>
<head>
<title>message</title>
</head>
<body>
<h1>${info }</h1>
</body>
</html>
如果Web项目和EJB项目在同一服务器中，那么象上面的程序运行是没什么问题的。如果Web项目和EJB项目不在同一台服务器中，或者同一台服务器中使用的不是JBOSS自带的Tomcat，那么需要修改一下servlet:
修改后的EJBServlet.java
package com.lovo.servlet;
import java.io.IOException;
import java.util.Hashtable;
import javax.ejb.CreateException;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.lovo.interfaces.Hello;
import com.lovo.interfaces.HelloHome;
public class EJBServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("gb2312");
String info = request.getParameter("info");
InitialContext context = null;
Hello hello = null;
/*********************添加的代码*****************************/
Hashtable environment = new Hashtable();
environment.put(Context.INITIAL_CONTEXT_FACTORY,
"org.jnp.interfaces.NamingContextFactory");
environment.put(Context.URL_PKG_PREFIXES,
"org.jboss.naming:org.jnp.interfaces");
environment.put(Context.PROVIDER_URL, "jnp://localhost:1099");
/***********************************************************/
try
{
context = new InitialContext(environment);
HelloHome home = (HelloHome) context.lookup("ejb/Hello");
hello = home.create();
}
catch (NamingException e)
{
e.printStackTrace();
}
catch (CreateException e)
{
e.printStackTrace();
}
info = hello.sayHello(info);
request.setAttribute("info", info);
request.getRequestDispatcher("message.jsp").forward(request, response);
}
}
光修改这里还不够，还需要将%jboss%/client/jbossall-client.jar 和EJB项目的jar包拷贝到web 项目中WEB-INF\lib目录下。
补充：在jsp或servlet中调用EJB时出现下面错误时：
04:03:33,714 INFO [STDOUT] java.rmi.ServerException: EJBException:; nested exception is:
javax.ejb.EJBException: Invalid invocation, check your deployment packaging, method=public abstract test.ejb.TestEJBInterface test.ejb.TestEJBHome.create() throws javax.ejb.CreateException,java.rmi.RemoteException
解决办法有三种：
1、编辑%jboss%/server/default/conf/jboss-service.xml
<mbean code="org.jboss.naming.NamingService"
name="jboss:service=Naming"
xmbean-dd="resource:xmdesc/NamingService-xmbean.xml">
<!-- The call by value mode. true if all lookups are unmarshalled using
the caller's TCL, false if in VM lookups return the value by reference.
-->
<attribute name="CallByValue">false</attribute>
...
</mbean>
将属性CallByValue的值改为true
2、编辑%jboss%/server/default/deploy/ear-deployer.xml
<mbean code="org.jboss.deployment.EARDeployer"
name="jboss.j2ee:service=EARDeployer">
<attribute name="Isolated">false</attribute>
<attribute name="CallByValue">false</attribute>
<attribute name="EnablelibDirectoryByDefault">true</attribute>
</mbean>
将属性Isolated和CallByValue的值改为true
3、编辑%jboss%/server/default/deploy/jboss-web.deployer/META-INF/jboss-service.xml
<attribute name="Java2ClassLoadingCompliance">false</attribute>
<attribute name="UseJBossWebLoader">false</attribute>
将属性Java2ClassLoadingCompliance和UseJBossWebLoader的值改为false，这里默认值一般都是false
一般情况下，使用第二种方式就可以解决该问题。
发表于 @ 2007年08月13日 14:50:00|评论(loading...)|编辑