问题:sevlet连接数据库无法加载驱动
sevlet连接数据库加载驱动的时候总是连接不上,但是在测试的程序中是可以连接并且读取的,代码如下所示:web.xml<servlet><servlet-name>DatabaseAccess</servlet-name><servlet-class>DatabaseAccess</servlet-cla...
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sevlet连接数据库加载驱动的时候总是连接不上,但是在测试的程序中是可以连接并且读取的,代码如下所示:
web.xml
<servlet>
<servlet-name>DatabaseAccess</servlet-name>
<servlet-class>DatabaseAccess</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DatabaseAccess</servlet-name>
<url-pattern>/DatabaseAccess</url-pattern>
</servlet-mapping>
DatabaseAccess.java
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class DatabaseAccess
*/
@WebServlet("/DatabaseAccess")
public class DatabaseAccess extends HttpServlet {
private static final long serialVersionUID = 1L;
// JDBC 驱动名及数据库 URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost:3306/RUNOOB";
// 数据库的用户名与密码,需要根据自己的设置
static final String USER = "root";
static final String PASS = "123456";
/**
* @see HttpServlet#HttpServlet()
*/
public DatabaseAccess() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Connection conn = null;
Statement stmt = null;
// 设置响应内容类型
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String title = "Servlet Mysql 测试 - 菜鸟教程";
String docType = "<!DOCTYPE html>\n";
out.println(docType +
"<html>\n" +
"<head><title>" + title + "</title></head>\n" +
"<body bgcolor=\"#f0f0f0\">\n" +
"<h1 align=\"center\">" + title + "</h1>\n");
try{
// 注册 JDBC 驱动器
Class.forName("com.mysql.jdbc.Driver");
// 打开一个连接
conn = DriverManager.getConnection(DB_URL,USER,PASS);
// 执行 SQL 查询
stmt = conn.createStatement();
String sql;
sql = "SELECT id, name, url FROM websites";
ResultSet rs = stmt.executeQuery(sql);
// 展开结果集数据库
while(rs.next()){
// 通过字段检索
int id = rs.getInt("id");
String name = rs.getString("name");
String url = rs.getString("url");
// 输出数据
out.println("ID: " + id);
out.println(", 站点名称: " + name);
out.println(", 站点 URL: " + url);
out.println("<br />");
}
out.println("</body></html>");
// 完成后关闭
rs.close();
stmt.close();
conn.close();
} catch(SQLException se) {
// 处理 JDBC 错误
se.printStackTrace();
} catch(Exception e) {
// 处理 Class.forName 错误
e.printStackTrace();
}finally{
// 最后是用于关闭资源的块
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
}
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
但是在实际测试中是可以的,
package com.company;
import java.sql.*;
public class Main {
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost:3306/runoob";
// 数据库的用户名与密码,需要根据自己的设置
static final String USER = "root";
static final String PASS = "1234";
public static void main(String[] args) throws ClassNotFoundException {
Statement stmt = null;
Connection conn = null;
try{
// 注册 JDBC 驱动器
Class.forName("com.mysql.jdbc.Driver");
System.out.println("数据库加载成功");
// 打开一个连接
conn = DriverManager.getConnection(DB_URL,USER,PASS);
System.out.println("数据库连接成功");
// 执行 SQL 查询
stmt = conn.createStatement();
String sql;
sql = "SELECT id, name, url FROM websites";
ResultSet rs = stmt.executeQuery(sql);
// 展开结果集数据库
while(rs.next()){
System.out.println("读取");
// 通过字段检索
int id = rs.getInt("id");
String name = rs.getString("name");
String url = rs.getString("url");
System.out.println(id+name+url);
// 输出数据
System.out.println("ID: " + id);
System.out.println(", 站点名称: " + name);
System.out.println(", 站点 URL: " + url);
System.out.println("<br />");
}
System.out.println("</body></html>");
// 完成后关闭
rs.close();
stmt.close();
conn.close();
} catch(SQLException se) {
// 处理 JDBC 错误
se.printStackTrace();
} catch(Exception e) {
System.out.println("数据库连接失败");
e.printStackTrace();
}finally{
// 最后是用于关闭资源的块
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
}
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}
}
}
}
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