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JSP连接数据库异常Context.lookup分析

1.数据库连接访问方式

JSP里面链接数据库操作如下: 

  Context ctx = new InitialContext();
  DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/bookstore");
  Connection conn = ds.getConnection();


   Statement stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
   ResultSet rs = stmt.executeQuery("select * from guestbook order by gst_time desc");
   

2.异常详细信息

登录到JSP页面时,抛出异常如下:

type Exception report

message javax.servlet.ServletException: org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class ‘‘ for connect URL ‘jdbc:mysql://localhost:3306/bookstore?autoReconnect=true‘

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: javax.servlet.ServletException: org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class ‘‘ for connect URL ‘jdbc:mysql://localhost:3306/bookstore?autoReconnect=true‘	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:502)	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:412)	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)	javax.servlet.http.HttpServlet.service(HttpServlet.java:723)

3.通过异常信息,定位问题
通过查看异常信息,发现 driver class为空,说明driver class配置不对
查看server.xml文件,配置如下:
  <Context path="/ch12" docBase="I:\Develop\Code\Chapter12" reloadable="true">
   <Resource name="jdbc/bookstore" auth="Container" type="javax.sql.DataSource"
    maxActive="100" maxIdle="30" maxWait="10000"
    username="root" password="root"
    dirverClassName="com.mysql.jdbc.Driver"
    url="jdbc:mysql://localhost:3306/bookstore?autoReconnect=true" />
  </Context>
通过观察发现,原本应该是“driverClassName”却误写成"dirverClassName"

将修正driverClassName之后,重启Tomcat,JSP网页访问正常

4.Context.lookup参数说明
  DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/bookstore");

说明:java:comp/env 是固定参数
   jdbc/bookstore 对应两个地方:
一个是:server.xml中的Resource  name
另一个:web.xml中的resource-ref  res-ref-name

详细配置:server.xml
(见上面第3步的异常定位)
  <Context path="/ch12" docBase="I:\Develop\Code\Chapter12" reloadable="true">
<Resource name="jdbc/bookstore" auth="Container" type="javax.sql.DataSource"
    maxActive="100" maxIdle="30" maxWait="10000"
    username="root" password="root"
   dirverClassName="com.mysql.jdbc.Driver"
    url="jdbc:mysql://localhost:3306/bookstore?autoReconnect=true" />
  </Context>

详细配置:web.xml

<resource-ref>

  <description>Mysql JDBC DataSource</description>

  <res-ref-name>jdbc/bookstore</res-ref-name>

  <res-type>javax.sql.DataSource</res-type>

  <res-auth>Container</res-auth>

</resource-ref> 

 

程序可以换成:

InitialContext context=new InitialContext();

Context evnContext = (Context)initContext.lookup("java:/comp/env");

DataSource dataSource = (DataSource)evnContext.lookup("jdbc/bookstore");

Connection con = dataSource.getConnection();

5.总结

  1)掌握通过页面抛出的异常信息,快速定位问题,解决问题

  2)掌握JSP的数据库连接方式配置和使用方法