服务器出现java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/mydb2的问题

Servlet问题与解决

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• ​​1.发现问题​​
• ​​2.归根结底能让一个Servlet连接数据库就是​​
• • • 
      
  • ​​2.1配置web.xml；（或者使用注解的方式）​​
  • ​​2.2创建Servlet服务器对象​​
  • ​​2.3在服务器对象的WEB-INF—lib—mysql.jdbc.×××（选择你数据库相对对应的版本）；​​
  • ​​2.4规范你的连接数据步骤，定不要忘记了写创建驱动的代码，否则Servlet会识别不了连接数据库的代码​​
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1.发现问题

1.1出现java.sql.SQLException等问题

​​废话不多说直接上图​​

java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/mydb2
  at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:703)
  at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:229)
  at xiaoge.DemoServlet.doPost(DemoServlet.java:26)
  at xiaoge.DemoServlet.doGet(DemoServlet.java:38)
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
23-Mar-2020 23:16:26.984 信息 [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory 把web 应用程序部署到目录 [G:\Tomcat8\apache-tomcat-8.5.51-windows-x64\apache-tomcat-8.5.51\webapps\manager]
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
  at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
  at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
  at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
  at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
  at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
  at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
  at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
  at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:543)
  at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
  at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
  at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:688)
  at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
  at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
  at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:609)
  at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
  at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:818)
  at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1623)
  at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
  at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
  at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
  at java.base/java.lang.Thread.run(Thread.java:844)

先看看我的代码

package xiaoge;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

/**
 * Created by Administrator on 2020/3/23 22:11
 * @author Administrator
 */
public class DemoServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String url = getServletConfig().getInitParameter("url");
        String username = getServletConfig().getInitParameter("username");
        String password = getServletConfig().getInitParameter("password");
        String driver = getServletConfig().getInitParameter("driver");
        try {
            Connection connection = DriverManager.getConnection(url,username,password);
        } catch (SQLException  e) {
            e.printStackTrace();
        }finally {
            {

            }
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

首先我是想使用最基础的web.xml来温习一下不使用框架自己写配置文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">
    <servlet>
        <servlet-name>testServlet</servlet-name>
        <servlet-class>xiaoge.DemoServlet</servlet-class>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/mydb2</param-value>
        </init-param>
        <init-param>
            <param-name>username</param-name>
            <param-value>root</param-value>
        </init-param>
        <init-param>
            <param-name>password</param-name>
            <param-value>1234</param-value>
        </init-param>
        <init-param>
            <param-name>driver</param-name>
            <param-value>com.jdbc.mysql.Driver</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>testServlet</servlet-name>
        <url-pattern>/demo01</url-pattern>
    </servlet-mapping>
</web-app>

​​（配置文件是没有问题的）​​ 但是为什么会出现上述的问题呢，我也思考了好久终结了下面几种的情况

我在创建这个Servlet连接数据库时出现了几个问题（我开始搞不明白）：

1.为什么在​​测试类中​​​创建一个连接数据库时，​​不用写数据库驱动​​​就可以连接，而在​​Servlet​​服务器不行？

​​测试类（非服务器）Test连接数据库​​

package xiaoge;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
 * Created by Administrator on 2020/3/23 22:59
 */
public class Test {
    public static void main(String[] args) {
        try {
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb2","root","1234");
            System.out.println(connection);
        } catch (SQLException e) {
            e.printStackTrace();
        }

    }

​​Servlet服务器类​​

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String url = getServletConfig().getInitParameter("url");
        String username = getServletConfig().getInitParameter("username");
        String password = getServletConfig().getInitParameter("password");
        String driver = getServletConfig().getInitParameter("driver");
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection connection = DriverManager.getConnection(url,username,password);
        } catch (SQLException | ClassNotFoundException e) {
            e.printStackTrace();
        }finally {
            {

            }
        }
    }

2.​​为什么连接数据库的jar包导在所有的类中，Servlet识别不了？非要你在WEB-INF下创建一个lib目录放进去连接jar包？​​（`所谓配置好了是，你能在测试类中可以连接数据库，而在服务器端连不上）
解决方法就是下图

2.归根结底能让一个Servlet连接数据库就是

2.1配置web.xml；（或者使用注解的方式）

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">
    <servlet>
        <servlet-name>testServlet</servlet-name>
        <servlet-class>xiaoge.DemoServlet</servlet-class>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/mydb2</param-value>
        </init-param>
        <init-param>
            <param-name>username</param-name>
            <param-value>root</param-value>
        </init-param>
        <init-param>
            <param-name>password</param-name>
            <param-value>1234</param-value>
        </init-param>
        <init-param>
            <param-name>driver</param-name>
            <param-value>com.jdbc.mysql.Driver</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>testServlet</servlet-name>
        <url-pattern>/demo01</url-pattern>
    </servlet-mapping>
</web-app>

2.2创建Servlet服务器对象

2.3在服务器对象的WEB-INF—lib—mysql.jdbc.×××（选择你数据库相对对应的版本）；

2.4规范你的连接数据步骤，定不要忘记了写创建驱动的代码，否则Servlet会识别不了连接数据库的代码

代码是：

​​Class.forname("com.jdbc.mysql.Driver");​​ 这个放在要连接的数据库connnerction 对象的前面；