学习JNDI创建数据库连接池出错

2012-03-06 11:50:23 183 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

Hibernate使用数据库连接池 java应用程序开发中，访问和操作数据库一般通过JDBC等技术实现，在基于数据库的web系统中，简历数据库连接的操作将是系统中代价最大的操作之一，通常成为制约网站速度的瓶颈。使用传统模式时，必须去管理每一个连接，确保它们能被正确关闭，如果出现程序异常而导致某些连接未能关闭，将导致数据库系统中的内存泄漏，最终将不得不重启数据库。连接池技术：初始化时先简历一些连接并存放在连接池中备用，阅读详情

出现这个错误
org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot load JDBC driver class 'com.mysql.jdbc.Driver'
无论是tomcat的lib 还是项目本身的lib 都有mysql-connector-java-5.1.18-bin.jar
Servlet代码：



package Servlet;



import java.io.IOException;

import java.io.PrintWriter;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.ResultSet;

import java.sql.PreparedStatement;

import java.sql.SQLException;



import javax.naming.NamingException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



public class ViewDictionary extends HttpServlet {

	/**

	 * 

	 */

	private static final long serialVersionUID = 1L;



	public void doGet(HttpServletRequest request, HttpServletResponse response)

			throws IOException, ServletException {

		response.setContentType("text/html;charset=UTF-8");

		PrintWriter out = response.getWriter();

		try {

			Connection conn=getFromJNDI();

			//Connection conn=getFromJDBC();

			PreparedStatement pstmt = conn

					.prepareStatement("SELECT * FROM t_dictionary ");

			ResultSet rs = pstmt.executeQuery();

			StringBuilder table = new StringBuilder();

			table.append("<table border='1'>");

			table.append("<tr><td>书名</td><td>价格</td></tr>");

			while (rs.next()) {

				table.append("<tr><td>" + rs.getString("english") + "</td><td>"

						+ rs.getString("chinese") + "</td></tr>");

			}

			table.append("</table>");

			out.println(table.toString());

			pstmt.close();

		} catch (Exception e) {

			System.out.println(e);

		}

	}

	public Connection getFromJNDI() throws NamingException, SQLException{

		javax.naming.Context ctx = new javax.naming.InitialContext();

		javax.sql.DataSource ds = (javax.sql.DataSource) ctx

				.lookup("java:/comp/env/jdbc/webdb");

		Connection conn = ds.getConnection();

		return conn;

	}

	public Connection getFromJDBC() throws ClassNotFoundException, SQLException{

		Class.forName("com.mysql.jdbc.Driver");

		String url="jdbc:mysql://localhost:3306/webdb?characterEncoding=UTF-8";

		Connection conn =DriverManager.getConnection(url,"root","123456");

		return conn;

	}

}

web.xml



<?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>ViewDictionary</servlet-name>

		<servlet-class>Servlet.ViewDictionary</servlet-class>

	</servlet>

	<servlet-mapping>

		<servlet-name>ViewDictionary</servlet-name>

		<url-pattern>/Servlet/ViewDictionary</url-pattern>

	</servlet-mapping>

	<resource-ref>

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

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

		<res-auth>Container</res-auth>

	</resource-ref>



	<welcome-file-list>

		<welcome-file>index.jsp</welcome-file>

	</welcome-file-list>

</web-app>

context.xml



<?xml version="1.0" encoding="UTF-8"?>

<Context>

	<Resource name="jdbc/webdb" quth="Container" type="javax.sql.DataSource"

		driverClassName="com.mysql.jdbc.Driver"

		url="jdbc:mysql://localhost:3306/webdb?characterEncoding=UTF-8"

		username="root" password="123456" maxActive="200" maxIdle="50"

		maxWait="3000" />

</Context>

...全文