我们可以从servlet打开mysql连接吗？ （使用mysql连接器）

Question

我有一个 DatabaseConnectionOpen.java 类，如下所示：

package db;

import java.sql.*;
public class DatabaseConnectionOpen {

static String dbHost = "jdbc:mysql://localhost:3306/javaweb?useSSL=false";
static String dbUsername = "user";
static String dbPassword = "user";

static Connection myConn = null;
static Statement myStmt = null;
static ResultSet myRes = null;

public void openConnection(){
    try {
        myConn = DriverManager.getConnection(dbHost, dbUsername, dbPassword);
    }
    catch (SQLException e) {
        e.printStackTrace();
    }
}
public ResultSet runQuery(String query){
    try{
        myStmt = myConn.createStatement();
        myRes = myStmt.executeQuery(query);
    }
    catch (SQLException e) {
        e.printStackTrace();
    }
    finally {
        return myRes;
    }
}
public void closeConnection(){
    try {
        if (myRes != null) myRes.close();
        if (myStmt != null) myStmt.close();
        if (myConn != null) myConn.close();
    }
    catch (SQLException e) {
        e.printStackTrace();
    }
}
}

当我从名为ViewUsers.java的类中使用它时，它的工作正常，其代码如下：

package dbImplement;

import db.DatabaseConnectionOpen;

import java.sql.ResultSet;
import java.sql.SQLException;

public class ViewUsers {

public static void main(String[] args) {

    ResultSet myRes = null;

    DatabaseConnectionOpen dbObject = new DatabaseConnectionOpen();

    dbObject.openConnection();

    try {
        myRes = dbObject.runQuery("SELECT * FROM users");
        while (myRes.next()) {
            System.out.println(myRes.getString("fname") + " " + myRes.getString("lname"));
        }
        myRes = dbObject.runQuery("SELECT * FROM users");
        while (myRes.next()) {
            System.out.println(myRes.getString("fname"));
        }
    }
    catch (SQLException e) {
        e.printStackTrace();
    }
    finally {
        dbObject.closeConnection();
    }

    dbObject.closeConnection();

}
}

但是当我想从servlet使用DatabaseConnectionOpen.java时会出现问题，代码如下：

package servlets;

import db.DatabaseConnectionOpen;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.ResultSet;
import java.sql.SQLException;

@WebServlet(name = "FirstServlet", urlPatterns = {"/msg"})

public class FirstServlet extends HttpServlet {

protected void doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) throws javax.servlet.ServletException, IOException {

    response.setContentType("text/html");
    PrintWriter out = response.getWriter();

    ResultSet myRes = null;
    DatabaseConnectionOpen dbObject = new DatabaseConnectionOpen();
    dbObject.openConnection();
    out.println("<h1>Hello Sevlet</h1>");

    try {
        myRes = dbObject.runQuery("SELECT * FROM users");
        while (myRes.next()) {
            out.println("<h3>"+myRes.getString("fname") + " " + myRes.getString("lname")+"</h3>");
        }
    }
    catch (SQLException e) {
        e.printStackTrace();
    }
    finally {
        dbObject.closeConnection();
    }

    dbObject.closeConnection();

}
}

它只打印＆＃34; Hello Servlet＆＃34;但不是h3部分，并说：

> java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/javaweb?useSSL=false
    at java.sql.DriverManager.getConnection(DriverManager.java:689)
    at java.sql.DriverManager.getConnection(DriverManager.java:247)
    at db.DatabaseConnectionOpen.runQuery(DatabaseConnectionOpen.java:28)
    at servlets.FirstServlet.doGet(FirstServlet.java:30)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)
Feb 16, 2017 2:14:30 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /opt/tomcat/webapps/manager
Feb 16, 2017 2:14:30 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deployment of web application directory /opt/tomcat/webapps/manager has finished in 100 ms

它说找不到驱动程序，但我有mysql连接器的外部库，而我的其他类（ViewUsers.java）可以同时工作，但不是Servlet。