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我試圖將我的java servlet程序在eclipse IDE中本地連接到我在web主機中創建的遠程SQL數據庫。servlet連接到遠程mysql
AdminLoginServlet-
package dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import model.Model;
public class Dao
{
private static String driver="com.mysql.jdbc.Driver";
private static String url="jdbc:mysql://xyz.com/devadmin_CustomerDatabasev1";
private static String username="USER";
private static String password="Password";
private static Connection con=null;
private static ResultSet rs=null;
public static Connection connect()
{
try
{
Class.forName(driver);
con=DriverManager.getConnection(url,username, password);
}
catch(ClassNotFoundException e)
{
e.printStackTrace();
}
catch(SQLException e)
{
e.printStackTrace();
}
return con;
}
public static ResultSet validate(Model m, String sql)
{
try
{
connect();
PreparedStatement ps=con.prepareStatement("select userid,password from adminlogin where userid='user' and password='password'");
rs=ps.executeQuery();
}
catch(SQLException e)
{
e.printStackTrace();
}
return rs;
}
}
我出現以下錯誤500的錯誤代碼的用戶界面 -
`HTTP Status 500 -type Exception report message description
The server encountered an internal error that prevented it from fulfilling this request.exception
java.lang.NullPointerException
dao.Dao.validate(Dao.java:40)
controller.AdminLoginServlet.doPost(AdminLoginServlet.java:41)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
注根源的完整堆棧跟蹤可在的Apache Tomcat/7.0 .47日誌。
的Apache Tomcat/7.0.47 ` 並在控制檯 -
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1702)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1547)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at dao.Dao.connect(Dao.java:22)
at dao.Dao.validate(Dao.java:39)
at controller.AdminLoginServlet.doPost(AdminLoginServlet.java:41)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [AdminLoginServlet] in context with path [/FirstApp] threw exception
java.lang.NullPointerException
at dao.Dao.validate(Dao.java:40)
at controller.AdminLoginServlet.doPost(AdminLoginServlet.java:41)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
以下錯誤我不知道如何着手或調試一塊code.Thanks的提前任何指針，任何人都可以提供。
編輯：（26個月，2017年） 我發現的Java到MySQL連接器從以下鏈接失蹤： http://www.ccs.neu.edu/home/kathleen/classes/cs3200/JDBCtutorial.pdf
但我不能將其添加到構建路徑作爲外部歸檔。我是得到下面的選項 -
預先感謝任何指針，任何人都可以提供。
'java.lang.ClassNotFoundException：com.mysql.jdbc.Driver'它在運行時在哪裏？ – nitind
@nitin我已經將它加載到lib中，並在主要問題中附加了屏幕截圖供參考。 –
1.將驅動程序jar文件放入Web應用程序庫，就像運行時需要的其他庫一樣（即在WebContent/WEB-INF/LIB）。從構建路徑中刪除它：所有的Web應用程序庫都隱含在構建路徑中。 2.不要在connect（）中捕獲和忽略異常。所有NullPointerExceptions隱藏原始原因：您無法連接。如果無法連接，則不應從connect（）方法返回。你應該拋出一個異常。 3.您的託管服務提供商很有可能不允許其網絡外部的連接。 –