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截止目前，同学们一共提了 132604个问题

老师，我io流输出了乱码怎么解决呢，代码都是一样的，是我idea编码有问题吗，怎么解决呢呢

JAVA 全系列/第二阶段：JAVA 基础深化和提高/网络编程 24886楼

老师，为啥对象的引用要向上呢，实例化自己不是更加确切嘛

JAVA 全系列/第二阶段：JAVA 基础深化和提高/容器（旧） 24887楼

wine_x,wine_y = datasets.load_wine(return_X_y=True)
return_X_y=True这个是什么意思？

Python 全系列/第二十三阶段：人工智能基础_机器学习理论与实战/KMeans聚类与降维算法 24888楼

哪里错啦

"C:\Program Files\Java\jdk-19\bin\java.exe" "-javaagent:D:\Program Files\IntelliJ IDEA 2022.3.2\lib\idea_rt.jar=1574:D:\Program Files\IntelliJ IDEA 2022.3.2\bin" -Dfile.encoding=UTF-8 -Dsun.stdout.encoding=UTF-8 -Dsun.stderr.encoding=UTF-8 -classpath C:\Users\hkn\IdeaProjects\jdbcdemo\out\production\jdbcdemo;C:\Users\hkn\IdeaProjects\jdbcdemo\lib\mysql-connector-java-5.1.48.jar itbaizhan.Test

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'valuer(default,'hkn',21)' at line 1

at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:67)

at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)

at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:484)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)

at com.mysql.jdbc.Util.getInstance(Util.java:408)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:944)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3933)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3869)

at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2524)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2675)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2439)

at com.mysql.jdbc.StatementImpl.executeInternal(StatementImpl.java:829)

at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:729)

at itbaizhan.StatementTest.insertUsers(StatementTest.java:25)

at itbaizhan.Test.main(Test.java:9)

Process finished with exit code 0

JAVA 全系列/第三阶段：数据库编程/JDBC技术 24889楼

有一个问题突然不明白了，就是在一对一users和roles，在对RolesMapper，我们构建的抽象类是Roles类型，然而在一对多里面，在OrdersMapper接口的抽象方法，返回的是List<Orders>，我自己的理解是：一对一，只有一条数据，就是返回Roles类型，如果是多条数据，我们就要用List泛型对吧？？

JAVA 全系列/第六阶段：项目管理与SSM框架/Mybatis 24890楼

webdemo.zip

老师我这不管输入用户名密码正确还是错误都报用户名密码错误，控制台会报下面的错误，是我数据库的问题吗麻烦老师帮我看看

java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/bjsxt?useUnicode=true&characterEncoding=utf-8
	at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:702)
	at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228)
	at com.bjsxt.commens.JdbcUtils.getConnection(JdbcUtils.java:30)
	at com.bjsxt.dao.impl.UserLoginDaoImpl.selectUsersByUserNameAndUserPwd(UserLoginDaoImpl.java:17)
	at com.bjsxt.service.Impl.UserLoginServiceImpl.userLogin(UserLoginServiceImpl.java:21)
	at com.bjsxt.web.servlet.UserLoginServlet.doPost(UserLoginServlet.java:29)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
	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 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
	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:690)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.base/java.lang.Thread.run(Thread.java:834)
java.lang.NullPointerException
	at com.bjsxt.dao.impl.UserLoginDaoImpl.selectUsersByUserNameAndUserPwd(UserLoginDaoImpl.java:18)
	at com.bjsxt.service.Impl.UserLoginServiceImpl.userLogin(UserLoginServiceImpl.java:21)
	at com.bjsxt.web.servlet.UserLoginServlet.doPost(UserLoginServlet.java:29)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
	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 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
	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:690)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.base/java.lang.Thread.run(Thread.java:834)

JAVA 全系列/第五阶段：JavaWeb开发/Web实战案例 24891楼

返闯关环节中为什么返回值不同，不是重载的标志，反而形参的顺序作为重载的标志

JAVA 全系列/第一阶段：JAVA 快速入门/控制语句、方法、递归算法 24892楼

老师，学了这么几节javaweb，明显感觉这玩意特抽象，不向javase那样比较的实在。这有没有啥学习的小技巧？