配置tomcat5.0连接池遇到的问题，请高人指点

我在使用tomcat5.0连接池功能时，得到的conn对象总是为空，真是郁闷，请高人指点。多谢多谢了！！！！
这是我的server.xml
<?xml version='1.0' encoding='utf-8'?>
<Server>
  <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener"/>
  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener"/>
  <GlobalNamingResources>
    <Environment name="simpleValue" type="java.lang.Integer" value="30"/>
    <Resource auth="Container" description="User database that can be updated and saved" name="UserDatabase" type="org.apache.catalina.UserDatabase"/>
    <Resource name="jdbc/hello" type="javax.sql.DataSource"/>
    <ResourceParams name="UserDatabase">
      <parameter>
        <name>factory</name>
        <value>org.apache.catalina.users.MemoryUserDatabaseFactory</value>
      </parameter>
      <parameter>
        <name>pathname</name>
        <value>conf/tomcat-users.xml</value>
      </parameter>
    </ResourceParams>
    <ResourceParams name="jdbc/hello">
      <parameter>
        <name>url</name>
        <value>jdbc:Oracle:thin@127.0.0.1:1521:jingrui</value>
      </parameter>
      <parameter>
        <name>passWord</name>
        <value>tiger</value>
      </parameter>
      <parameter>
        <name>maxActive</name>
        <value>4</value>
      </parameter>
      <parameter>
        <name>maxWait</name>
        <value>5000</value>
      </parameter>
      <parameter>