真心被JDBC搞死了 MySQL弄了一个星期还是连接报错
win7 + jdk 1.7 + mySQL 5.5 + Tomcat 6
Mysql 安装没问题，命令行进去 show datebases 新建表 加数据乱七八糟都没问题
Tomcat没问题，叮叮当当调了好多servlet 正常
然后 调了这个噩梦般的程序：
- Java code
package org.sunxin.lesson.jsp.bookstore;import javax.servlet.*;import java.io.*;import javax.servlet.http.*;import java.sql.*;public class CreateDBServlet extends HttpServlet{ private String url; private String user; private String password; public String errortext; public void init() throws ServletException { String driverClass=getInitParameter("driverClass"); url=getInitParameter("url"); user=getInitParameter("user"); password=getInitParameter("password"); try { Class.forName(driverClass); } catch(ClassNotFoundException ce) { errortext="加载数据库驱动失败！"; } } public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,IOException { Connection conn=null; Statement stmt=null; try { conn=DriverManager.getConnection(url,user,password); stmt=conn.createStatement(); stmt.executeUpdate("create database bookstore"); stmt.executeUpdate("use bookstore"); stmt.executeUpdate("create table bookinfo(id INT not null primary key,title VARCHAR(50) not null,author VARCHAR(50) not null,bookconcern VARCHAR(100) not null,publish_date DATE not null,price FLOAT(4,2) not null,amount SMALLINT,remark VARCHAR(200)) ENGINE=InnoDB"); stmt.addBatch("insert into bookinfo values(1,'Java从入门到精通','张三','张三出版社','2004-6-1',34.00,35,null)"); stmt.addBatch("insert into bookinfo values(2,'JSP深入编程','李四','李四出版社','2004-10-1',56.00,20,null)"); stmt.addBatch("insert into bookinfo values(3,'J2EE高级编程','王五','王五出版社','2005-3-1',78.00,10,null)"); stmt.executeBatch(); PrintWriter out=resp.getWriter(); out.println(errortext); out.println("success!"); out.close(); } catch(SQLException se) { se.printStackTrace(); } finally { if(stmt!=null) { try { stmt.close(); } catch(SQLException se) { se.printStackTrace(); } stmt=null; } if(conn!=null) { try { conn.close(); } catch(SQLException se) { se.printStackTrace(); } conn=null; } } }}Tomcat6的 web.xml 里配置如下：
- Java code
<context-param> <param-name>driverClass</param-name> <param-value>com.mysql.jdbc.Driver</param-value> </context-param> <context-param> <param-name>url</param-name> <param-value>jdbc:mysql://localhost:3306/mysql</param-value> </context-param> <context-param> <param-name>user</param-name> <param-value>root</param-value> </context-param> <context-param> <param-name>password</param-name> <param-value>root</param-value> </context-param> <servlet> <servlet-name>CreateDBServlet</servlet-name> <servlet-class>org.sunxin.lesson.jsp.bookstore.CreateDBServlet</servlet-class> </servlet>
启动tomcat 访问这个servlet 报错：
- XML code
HTTP Status 500 -------------------------------------------- type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: Servlet.init() for servlet CreateDBServlet threw exception org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291) org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602) org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) java.lang.Thread.run(Unknown Source)root cause java.lang.NullPointerException java.lang.Class.forName0(Native Method) java.lang.Class.forName(Unknown Source) org.sunxin.lesson.jsp.bookstore.CreateDBServlet.init(CreateDBServlet.java:23) javax.servlet.GenericServlet.init(GenericServlet.java:212) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291) org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602) org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) java.lang.Thread.run(Unknown Source)note The full stack trace of the root cause is available in the Apache Tomcat/6.0.33 logs.
真心调的筋疲力竭了，已经下了 mysql-connector-java-5.1.18-bin.jar 放到了D:\Tomcat\lib
[解决办法]
好吧 ，给你分析一下
1. 空指针一定是你的getInitParameter("driverClass")没有取到值。。。因为你用字符串替代后，没有报错空指针。。。
2. stmt.executeUpdate("create database bookstore");
stmt.executeUpdate("use bookstore");
这两句就是你页面空白的原因。
看看你的连接语句：url="jdbc:mysql://localhost:3306/mysql";这里的mysql指的数据库名吧。。。你连接了mysql数据库，进去操作的却是bookstore，本身这么做 就是有问题的。。。这样写代码怎么行？并在mysql命令行打命令才这么去用，你却把它用到了java连接sql的时候，不规范。。。还有你为什么不能直接连接bookstore数据库？
日志中写的很清楚了。你的bookstore数据库已经存在了。你还要用这条命令create database bookstore去再次创建数据库！！！！就出错啦。。。
修改：
去掉stmt.executeUpdate("create database bookstore");
stmt.executeUpdate("use bookstore");
两行代码。。
然后连接url="jdbc:mysql://localhost:3306/bookstore";
[解决办法]
楼主，你这些语句获得的值都是空的，不信你自己打出来看一下
- Java code
String driverClass=getInitParameter("driverClass"); url=getInitParameter("url"); user=getInitParameter("user"); password=getInitParameter("password");
我的异常网推荐解决方案：The server encountered an internal error () that prevented it from fulfilling this request.,http://www.myexception.cn/java-web/317.html