通过读取web.xml文件中的配置参数连接数据库
1.问题提出
-javax.servlet.ServletException: Servlet.init() for servlet CreateDBServlet threw exception
这个错误是在看孙鑫老师的那本web编程详解,在第八章遇见的,就是第一个例子
但总是运行不成功。仔细观察发现自己犯了两个错误。
(1)CreateDBServlet.java代码
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 void init() throws ServletException
{
String driverClass=getInitParameter("driverClass");
url=getInitParameter("url");
user=getInitParameter("user");
password=getInitParameter("password");
try
{
Class.forName(driverClass);
}
catch(ClassNotFoundException ce)
{
throw new UnavailableException("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("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;
}
}
}
}
(2)没有修改的web.xml
<?xml version="1.0" encoding="gb2312"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
version="2.4">
<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/bookstore</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>12345678</param-value>
</context-param>
<servlet>
<servlet-name>CreateDBServlet</servlet-name>
<servlet-class>org.sunxin.lesson.jsp.bookstore.CreateDBServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CreateDBServlet</servlet-name>
<url-pattern>/createdb</url-pattern>
</servlet-mapping>
2.问题解决
(1)stmt.executeUpdate("create database bookstore");
将这句代码注释掉,因为还没有创建数据库,那用conn=DriverManager.getConnection(url,user,password);连接数据库时,就会出问题,而且你要自己手动先create一个数据库,(create database bookstore;)这是mysql的命令就不多说了。
(2)编辑web.xml如下(注意修改你的数据库密码)
<servlet>
<servlet-name>CreateDBServlet</servlet-name>
<servlet-class>org.sunxin.lesson.jsp.bookstore.CreateDBServlet</servlet-class>
<init-param>
<param-name>driverClass</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/bookstore</param-value>
</init-param>
<init-param>
<param-name>user</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>password</param-name>
<param-value>1234</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>CreateDBServlet</servlet-name>
<url-pattern>/createdb</url-pattern>
</servlet-mapping>
然后把这个配置文件放到你的应用程序的WEB-INF目录下,注意WEB-INF目录一定要在你的程序的目录下,且为第一层目录。
这里还有一个问题就是,如我们没有手动创建自己的数据库,服务器并不给出错误提示,但也不会得到正确结果,浏览器只显示空白页,不知道为什么,如果谁知道这个问题的解决办法,可以通知我,我会非常的感谢,可以给我留言,也可以qq联系我。
我是用的tomcat6+jdk1.5+mysql5调试成功的。
Qq:124273269