请教如何访问MYSQL数据库？

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 ServletException("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
{
stmt=conn.createStatement();
stmt.executeUpdate("create datebase 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-data DATA not null,price FLOAT(4,2) not null,amount SMALLINT,re VARCHAR(200))ENGINE=InnoDB");
stmt.addBatch("insert into bookinfo values(1,'java Web开发','孙鑫','电子工业出版社','2006-4-20',99.00,35,null)");
stmt.executeBatch();
resp.setContentType("text/html;charset=GBK");
PrintWriter out=resp.getWriter();
out.println("数据库加载成功");
out.close();
}
catch (SQLException se)
{
throw new ServletException(se);
}
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;
}
}
}
}
<?xml version="1.0" encoding="gb2312"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5"><servlet>
<servlet-name>CreateDBServlet</servlet-name>
<servlet-class>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</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>12345678</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>CreateDBServlet</servlet-name>
<url-pattern>/createdb</url-pattern>
</servlet-mapping></web-app>启动TOMCAT之后 访问http://localhost:8080/ch04/createdb出现如下错误
HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception java.lang.NullPointerException
CreateDBServlet.doGet(CreateDBServlet.java:38)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.6 logs.
初次使用数据库，还请指点 不胜感激

解决方案 »

  1.   

    当我重新编译时 tomcat提示
    the web application [/ch04] registered the JDBC driver [com.mysql.jdbc.Driver] but failes to unregister it when the web qpplication was stopped. To prevent a memory leak,the JDBC Driver has been forcibly unregistered
      

  2.   


    你已经获得了数据库连接了，但是还报错，我想是你的WEB.XML里没有配置数据库。    <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/数据库名字</param-value>
        </init-param>我的清单：
    <?xml version="1.0" encoding="UTF-8"?>
    <web-app version="2.5" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
      <servlet>
        <servlet-name>CreateDBServlet</servlet-name>
        <servlet-class>com.zhuchao.servlet.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://127.0.0.1:3306/hibernate</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>zhuchao</param-value>
        </init-param>    
      </servlet>
      <servlet-mapping>
        <servlet-name>CreateDBServlet</servlet-name>
        <url-pattern>/CreateDBServlet</url-pattern>
      </servlet-mapping>
      <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
      </welcome-file-list>
    </web-app>package com.zhuchao.servlet;
    import java.io.IOException;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    public class CreateDBServlet extends HttpServlet {
    private static final long serialVersionUID = 4504905042789200456L;
    private static String driverClass;
    private static String url;
    private static String user;
    private static String password;
    public CreateDBServlet() {
    super();
    }
    public void destroy() {
    super.destroy();
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    doPost(request, response);
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    driverClass=getInitParameter("driverClass");
            url=getInitParameter("url");
            user=getInitParameter("user");
            password=getInitParameter("password");         
            System.err.println(driverClass+url+user+password);
    Connection connection=null;
    try {
    Class.forName(driverClass);
    connection = DriverManager.getConnection(url,user,password);
    if (connection!=null) {
    System.err.println("获的连接");
    int i=0;
    PreparedStatement preparedStatement = connection.prepareStatement("SELECT COUNT(*) FROM tb_company WHERE LEVEL =0 ");
    ResultSet resultSet = preparedStatement.executeQuery();
    if(resultSet.next()){
    i=resultSet.getInt(1);
    System.err.println("结果："+i);
    }
    resultSet.close();
    preparedStatement.close();
    connection.close();
    connection.close();
    }else {
    System.err.println("未获取连接");
    }
    } catch (Exception e) {
    e.printStackTrace();
    }
    }
    public void init() throws ServletException {
    driverClass=getInitParameter("driverClass");
            url=getInitParameter("url");
            user=getInitParameter("user");
            password=getInitParameter("password"); 
    }
    }我的结果：
    com.mysql.jdbc.Driverjdbc:mysql://127.0.0.1:3306/hibernaterootzhuchao
    获的连接
    结果：6
      

  3.   

    Connection conn=null;
    stmt=conn.createStatement();
    你没初始化conn就用它了 当然会空指针了
      

  4.   

    确实少了这句，可是加上以后还是不对
    HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: java.sql.SQLException: Can't create database 'bookstore'; database exists
    CreateDBServlet.doGet(CreateDBServlet.java:52)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    root cause java.sql.SQLException: Can't create database 'bookstore'; database exists
    com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
    com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3593)
    com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3525)
    com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1986)
    com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2140)
    com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2620)
    com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1662)
    com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1581)
    CreateDBServlet.doGet(CreateDBServlet.java:40)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    note The full stack trace of the root cause is available in the Apache Tomcat/7.0.6 logs.怎么无法创建bookstore呢
      

  5.   

    这句语法是否有问题呢？小弟不太懂SQL语句，正准备学。呵呵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-data DATA not null,price FLOAT(4,2) not null,amount SMALLINT,re VARCHAR(200))ENGINE=InnoDB");
      

  6.   


    你把
    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-data DATA not null,price FLOAT(4,2) not null,amount SMALLINT,re VARCHAR(200))ENGINE=InnoDB放到查询分析器里 执行一边 如果 可以创建数据库 那就能行了。
      

  7.   

    java.sql.SQLException: Can't create database 'bookstore'; database exists
    这句，已经存在'bookstore'这个database了，改名字或者在database里面删去
      

  8.   

    同样问题总是提示HTTP Status 404错误