pst = conn.prepareStatement("select * from admin where userName=?");    pst.setString(1,userName);

    ResultSet rs=pst.executeQuery();

    boolean isExist=false;

 if(rs.next()){isExist=true;}        out.println(isExist);

} catch (SQLException e) {

e.printStackTrace();

}      

out.close();

}

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

    }

    public void init() throws ServletException {

    }

}

4.3  web.xml配置文件中Servlet说明

…

<servlet>

<servlet-name>CheckUserName</servlet-name>    <servlet-class>czz.com.CheckUserName</servlet-class>

  </servlet>

<servlet_mapping>

 <servlet-name>CheckUserName</servlet-name>    <url-pattern>/CheckUserName</url-pattern>

</servlet-mapping>

…

4.4  运行效果

站点的部署在此不做讲述，运行成功后，如图2所示。用户可以输入信息进行注册了。

图 2 注册页面