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    JDBC连接mysql数据库测试的时候可以连接上，但是在Tomcat里面就连接不上了，不知道为啥？
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    0 
    java.sql.SQLException: Unknown character set index for field '255' received from server.
    at com.mysql.jdbc.Connection.getCharsetNameForIndex(Connection.java:1679)
    at com.mysql.jdbc.Field.<init>(Field.java:161)
    at com.mysql.jdbc.MysqlIO.unpackField(MysqlIO.java:510)
    at com.mysql.jdbc.MysqlIO.getResultSet(MysqlIO.java:285)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1325)
    at com.mysql.jdbc.MysqlIO.sqlQuery(MysqlIO.java:1224)
    at com.mysql.jdbc.Connection.execSQL(Connection.java:2248)
    at com.mysql.jdbc.Connection.execSQL(Connection.java:2196)
    at com.mysql.jdbc.Statement.executeQuery(Statement.java:1163)
    at com.mysql.jdbc.Connection.loadServerVariables(Connection.java:3419)
    at com.mysql.jdbc.Connection.initializePropsFromServer(Connection.java:3254)
    at com.mysql.jdbc.Connection.createNewIO(Connection.java:1803)
    at com.mysql.jdbc.Connection.<init>(Connection.java:450)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:411)
    at java.sql.DriverManager.getConnection(DriverManager.java:664)
    at java.sql.DriverManager.getConnection(DriverManager.java:247)
    at com.bmd.util.DbUtil.<clinit>(DbUtil.java:15)
    at com.bmd.dao.mDao.findPaging(mDao.java:161)
    at com.bmd.service.MessageServlet.doPost(MessageServlet.java:75)
    at com.bmd.service.MessageServlet.doGet(MessageServlet.java:28)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    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:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at com.bmd.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:35)
    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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:384)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312)
    at org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:531)
    at org.apache.jsp.index_jsp._jspService(index_jsp.java:129)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:444)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
    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:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at com.bmd.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:35)
    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:494)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
    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:412)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1385)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
五月 12, 2018 8:39:54 下午 org.apache.catalina.core.ApplicationDispatcher invoke
严重: Servlet.service() for servlet [MessageServlet] threw exception
java.lang.NullPointerException
    at com.bmd.dao.mDao.findPaging(mDao.java:163)
    at com.bmd.service.MessageServlet.doPost(MessageServlet.java:75)
    at com.bmd.service.MessageServlet.doGet(MessageServlet.java:28)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    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:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at com.bmd.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:35)
    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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:384)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312)
    at org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:531)
    at org.apache.jsp.index_jsp._jspService(index_jsp.java:129)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:444)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
    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:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at com.bmd.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:35)
    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:494)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
    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:412)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1385)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

    在单个java文件测试的时候是可以连接的，同样环境下面，配置到tomcat后就出现错误

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    • 冷血刺客 普通会员 1楼

      在Tomcat中无法连接MySQL数据库，可能是以下原因：

      1. Tomcat配置错误：请检查Tomcat的配置文件，确认是否正确配置了数据库连接参数（如数据库名、主机名、端口等）。

      2. 数据库服务未启动：确保数据库服务已经启动。可以通过在Tomcat的bin目录下运行以下命令启动数据库服务： catalina.sh run 或者在Web.xml中添加以下语句启动数据库服务： xml <web-app> <servlet> <servlet-name>DBServlet</servlet-name> <servlet-class>com.mysql.jdbc.DriverServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>DBServlet</servlet-name> <url-pattern>/db</url-pattern> </servlet-mapping> </web-app>

      3. 数据库服务器故障：如果数据库服务器出现问题，可能会导致无法连接到数据库。请尝试重启数据库服务器或者联系数据库服务提供商进行问题排查。

      4. 数据库连接池问题：如果Tomcat中没有正确配置数据库连接池，也可能会导致无法连接到数据库。请检查Tomcat的配置文件，确保数据库连接池的配置正确。

      5. MySQL数据库问题：如果MySQL数据库出现问题，也可能会导致无法连接到数据库。请检查MySQL数据库的配置文件，确保数据库配置正确。

      希望以上信息能够帮助您解决问题。如果问题仍然存在，建议您详细描述您的问题，以便我们提供更专业的帮助。

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