初学ejb，在sessionbean里测试数据库的链接
HelloBean.java的源码如下：

package net.eschool.test;

import javax.ejb.*;
import java.util.*;
import java.sql.*;
import javax.sql.DataSource;
import javax.rmi.*;
import javax.naming.*;

public class HelloBean implements SessionBean {
  SessionContext sessionContext;
  public void ejbCreate() throws CreateException {
    /**@todo Complete this method*/
  }
  public void ejbRemove() {
    /**@todo Complete this method*/
  }
  public void ejbActivate() {
    /**@todo Complete this method*/
  }
  public void ejbPassivate() {
    /**@todo Complete this method*/
  }
  public void setSessionContext(SessionContext sessionContext) {
    this.sessionContext = sessionContext;
  }
  public String SayHello()
      throws NamingException, SQLException
  {

    InitialContext ctx = new InitialContext();
    DataSource ds = (DataSource) ctx.lookup("java:/OracleDS");     Connection conn = ds.getConnection();

    conn.close();
    return new String("Hello World");
  }
}

编译打包后在jboss3部署，后台日志无误，在jsp里调用该ejb错误如下：
java.rmi.UnmarshalException: Error unmarshaling return; nested exception
is: 
java.lang.ClassNotFoundException: org.jboss.resource.ResourceException (no security manager: RMI class loader disabled)
at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:217)
at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:133)
at org.jboss.invocation.jrmp.server.JRMPInvoker_Stub.invoke(Unknown Source)
at org.jboss.invocation.jrmp.interfaces.JRMPInvokerProxy.invoke(JRMPInvokerProxy.java:138)
at org.jboss.invocation.InvokerInterceptor.invoke(InvokerInterceptor.java:108)
at org.jboss.proxy.TransactionInterceptor.invoke(TransactionInterceptor.java:77)
at org.jboss.proxy.SecurityInterceptor.invoke(SecurityInterceptor.java:80)
at org.jboss.proxy.ejb.StatelessSessionInterceptor.invoke(StatelessSessionInterceptor.java:111)
at org.jboss.proxy.ClientContainer.invoke(ClientContainer.java:76)
at $Proxy1.SayHello(Unknown Source)
at _school._test__jsp._jspService(/school/test.jsp:43)
at com.caucho.jsp.JavaPage.service(JavaPage.java:75)
at com.caucho.jsp.Page.subservice(Page.java:485)
at com.caucho.server.http.FilterChainPage.doFilter(FilterChainPage.java:182)
at com.caucho.server.http.Invocation.service(Invocation.java:312)
at com.caucho.server.http.CacheInvocation.service(CacheInvocation.java:135)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:221)
at com.caucho.server.http.HttpRequest.handleConnection(HttpRequest.java:163)
at com.caucho.server.TcpConnection.run(TcpConnection.java:137)
at java.lang.Thread.run(Thread.java:536)
Caused by: java.lang.ClassNotFoundException: org.jboss.resource.ResourceException
(no security manager: RMI class loader disabled)
at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:368)
at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:159)
at java.rmi.server.RMIClassLoader$2.loadClass(RMIClassLoader.java:629)
at java.rmi.server.RMIClassLoader.loadClass(RMIClassLoader.java:257)
at sun.rmi.server.MarshalInputStream.resolveClass(MarshalInputStream.java:200)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1503)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1425)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1616)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1264)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1830)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1756)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1636)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1264)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:322)
at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:215)
... 19 more


这是怎么回事？

你把
　　InitialContext ctx = new InitialContext();
    DataSource ds = (DataSource) ctx.lookup("java:/OracleDS");     
换成
  javax.naming.Context jndiContext;
   jndiContext = new InitialContext();
   DataSource ds = (DataSource)jndiContext.lookup("java:/OracleDS");
试试