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对于初学像我这样初学EJB的菜鸟来讲，EJB的配置是一件非常繁琐的事情，不堪回首啊。呵呵，今天终于明白了昨天晚上遇到的一个白痴错误，所以将一个简单的例子写下来。
我这个例子的前提是EJB已经发布成功，在servlet中对已经发布的EJB的调用。
首先已要做的就是将已发布的EJB组件的jar文件拷贝到当前Web工程的lib下，其目录结构为：
EJB端：
    EJBFolderName
          |
          |------classes 
          |            |
          |            |-------hello
          |            |           |---------hello.class   //Remote
          |            |           |---------helloHome.class   //Home
          |            |           | ---------helloBean.class  //Bean
          |            |
          |            |--------META-INF
          |                           |------ejb-jar.xml  //EJB配置文件
            |                           |------MANIFEST.MF  //Manifest-Version: 1.0  Class-Path:
          | 
          |-----------src
                       |
                       |-------hello
                       |           |---------hello.java    //Remote
                       |           |---------helloHome.java    //Home
                       |           | ---------helloBean.java  //Bean
                       |
                       |--------META-INF
                                     |----ejb-jar.xml //servlet配置文件
                                     |-----MANIFEST.MF  //Manifest-Version: 1.0  Class-Path:

servlete端：
ServletFolderName
          |
          |----------src
          |            |-------hello
          |            |          |--------TestEJB.java  //被Servlet（只为目标清晰，也可直接写到Servlet内）
          |            |
          |            |-------TestEJBServlet.java  //一个Servlet  调用 包hello 中的方法。
          |
          |
          |----------WebRoot

                           |----------META-INF
                           |                  |--------MANIFEST.MF    //Manifest-Version: 1.0       Class-Path:
                           |
                           |----------WEB-INF
                                            |----------classes
                                            |               |-----------TestEJBServlet.class
                                            |               |
                                            |               | -----------hello                                              |                               |----------TestEJB.class
                                            |-----------lib              
                                            |            |----------FirstEJB.jar   //EJB打好的一个Jar包！EJB2.0不可缺少  

                                            |                           
                                            |------------web.xml   //Servlet配置文件             

基本文件结构就是这样。结束！         

*/下面是针对每个文件的详细说明：//首先是Servlet端，Servlet有一个servlet文件，实现doGet方法和doPost方法，还有一个Servlet配置文件 web.xml
//TestEJBServlet.java：

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import hello.TestEJB;
public class TestEJBServlet extends HttpServlet {
protected void doGet(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
this.doPost(request,response);  //直接以页面的形式调用Servlet 调用的事doGet方法，
//也可以直接在doGet方法中调用EJB
}
public void doPost(HttpServletRequest request, HttpServletResponse response){
try{
new TestEJB("iiop://localhost:2809/").test();  //调用 TestEJB.java 中的test()方法。
} catch(Exception e){
e.printStackTrace();
}
}
}

//TestEJB.java:

package hello;
import javax.naming.Context;
import java.util.Properties;
import javax.naming.NamingException;
import javax.naming.InitialContext;
import javax.rmi.PortableRemoteObject;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
public class TestEJB {
private static final String JNDI_NAME = "HelloEJB";  //EJB上传websphere时用的JNDI Name
private String url;
private HelloHome home;
public TestEJB(String url) throws NamingException{
this.url = url;
home = lookUpHome();
}
private Context getInitialContext() throws NamingException {
Properties prop = new Properties();
prop.put(Context.INITIAL_CONTEXT_FACTORY,"com.ibm.websphere.naming.WsnInitialContextFactory");
prop.put(Context.PROVIDER_URL, url);
return new InitialContext(prop);
}
private HelloHome lookUpHome() throws NamingException{
Context ctx = getInitialContext();
Object home = ctx.lookup(JNDI_NAME);
return (HelloHome)PortableRemoteObject.narrow(home,HelloHome.class);
}
public void test() throws RemoteException,CreateException,NamingException {
Hello hello = (Hello)PortableRemoteObject.narrow(home.create(),Hello.class);
System.out.println(hello.sayHello());
}
/*public static void main(String args[]) throws Exception{
try{
new TestEJB("iiop://localhost:2809/").test();
}catch(Exception e){
e.printStackTrace();
}
}*/
}

//Servlet 配置文件 web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet>
<servlet-name>TestEJB</servlet-name>
<servlet-class>TestEJBServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>TestEJBServlet</servlet-name>  //Servlet映射到web服务器上的名字
<url-pattern>/servlet/TestEJBServlet</url-pattern>//Servlet映射到web服务器上的路径
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>//默认开始页面（可有可无）
</welcome-file-list>
</web-app>

接下来是EJB端：三个java文件（Home.java,Remote.java,Bean.java）和一个ejb-jar配置文件
helloHome.java(就是Home.java  本地接口)

package hello;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.EJBHome;
public interface HelloHome extends EJBHome {
public Hello create()throws CreateException,RemoteException;
}

hello.java(就是Remote.java  远程接口)

package hello;
import java.rmi.RemoteException;
import javax.ejb.EJBObject;
public interface Hello extends EJBObject {
public String sayHello()throws RemoteException;
}

helloBean.java(就是Bean.java 实现类)

package hello;
import java.rmi.RemoteException;
import javax.ejb.EJBException;
import javax.ejb.CreateException;
import javax.ejb.SessionBean;
import javax.ejb.SessionContext;
public class HelloBean implements SessionBean {
private SessionContext ctx;
private String words ;
public String sayHello(){
System.out.println("i am in an EJB server."+words);
return words;
}
public void ejbCreate() throws CreateException{
this.words = "hello world";
}
public void ejbActivate() throws EJBException, RemoteException {
// TODO Auto-generated method stub
}
public void ejbPassivate() throws EJBException, RemoteException {
// TODO Auto-generated method stub
}
public void ejbRemove() throws EJBException, RemoteException {
// TODO Auto-generated method stub
}
public void setSessionContext(SessionContext arg0) throws EJBException,
RemoteException {
this.ctx = arg0;
}
}

还有一个配置文件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>
<display-name>HelloEjb</display-name>
<enterprise-beans>
<session>
<ejb-name>FirstEJB</ejb-name>
<home>hello.HelloHome</home>
<remote>hello.Hello</remote>
<ejb-class>hello.HelloBean</ejb-class>
<session-type>Stateless</session-type>
<transaction-type>Container</transaction-type>
</session>
</enterprise-beans>
<assembly-descriptor>
<container-transaction>
<method>
<ejb-name>FirstEJB</ejb-name>
<method-intf>Remote</method-intf>
<method-name>*</method-name>
</method>
<trans-attribute>Required</trans-attribute>
</container-transaction>
</assembly-descriptor>
</ejb-jar>

最后还想说一下对EJB的调用的集中方式，主要有三种：
1、用property帮助设置环境

Properties properties = System.getProperties();
properties.put(Context.PROVIDER_URL, "iiop://localhost:2809");
properties.put(Context.INITIAL_CONTEXT_FACTORY,"com.ibm.websphere.naming.WsnInitialContextFactory");
Context ctx = new InitialContext(properties);

2、用Hashtable帮助设置环境

Hashtable environment = new Hashtable();
environment.put(Context.INITIAL_CONTEXT_FACTORY,"com.ibm.websphere.naming.WsnInitialContextFactory");
environment.put(Context.PROVIDER_URL, "iiop://localhost:2809");  //可选，同“corbaloc:iiop:localhost:2809”的效果一样。
Context ctx= new InitialContext(environment);

3、WAS默认的方法