求助JSP中遇到的奇怪问题？

java中的代码：运行结果是yes
try{
         String ip="127.0.0.1",port="1433",username="sa",password="",dbname="hero";
         Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver"); 
         String db_url="jdbc:microsoft:sqlserver://"+ip+":"+port+";User="+username+";Password="+password+";DatabaseName="+dbname+";";
         conn = DriverManager.getConnection(db_url);  
         stmt = conn.createStatement();
         System.out.print("yes");
       }                                                                         
      catch(Exception e)                                                     
      {  
        System.out.print("no");
      }  
JSP中的代码：运行结果是no     
<% String ip="127.0.0.1",port="1433",username="sa",password="",dbname="hero";
try{
         Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");         
String db_url="jdbc:microsoft:sqlserver://"+ip+":"+port+";User="+username+";Password="+ password+";DatabaseName="+dbname+";";
         conn = DriverManager.getConnection(db_url);  
       stmt = conn.createStatement();                     
        out.println("yes");    
       }                                                                         
      catch(Exception e)                                                     
      {  
        e.printStackTrace();
         out.println("no");
      } 
%>
两段完全一样的代码，运行结果不一样。我发现原来是在JSP中
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver"); 加载驱动程序失败，这句发生异常，但是为什么在JAVA文件中这句执行是成功的？