虚拟机未正常关机，结果启动时崩溃了，数据库中有很多重要的数据，可以恢复吗？

这个是什么

对于thinkphp不是很理解，在db这块的应用。

希望大家可以解下惑，谢谢

我用普通用户的身份添加了一个crontab任务：

0 16 * * * xxxxxxx

过了时间没有执行，查看crontab.log也没有报错日志。

咋回事呢？

如果没有，该如何确保队列中数据是不重复的呢呢

web.xml 关键配置, 可以确定的是配置顺序没有问题

<!-- 安全过滤 -->
	<filter>
		<filter-name>shiroFilter</filter-name>
		<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
		<async-supported>true</async-supported>
		<init-param>
			<param-name>targetFilterLifecycle</param-name>
			<param-value>true</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>shiroFilter</filter-name>
		<url-pattern>*.do</url-pattern>
		<url-pattern>*.json</url-pattern>
		<url-pattern>*.xhtml</url-pattern>
	</filter-mapping>
	
	<!-- SpringMVC功能 -->
	<servlet>
		<servlet-name>dispatcher</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>/META-INF/spring/appconf-*.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
		<async-supported>true</async-supported>
	</servlet>
	<servlet-mapping>
		<servlet-name>dispatcher</servlet-name>
		<url-pattern>*.do</url-pattern>
		<url-pattern>*.json</url-pattern>
		<url-pattern>*.xhtml</url-pattern>
	</servlet-mapping>

控制器代码1, 像这样加入异步处理，正常响应，但是后台报错

/**
	 * 分页查询
	 * 
	 * @param queryVo
	 * @return　Pagination<DynamicformVo>
	 */
	@RequestMapping("queryPage")
	@ResponseBody
	public Callable<Pagination<DynamicformVo>> getGrid(@ModelAttribute("DynamicformQueryVo") final DynamicformQueryVo queryVo) {
		return new Callable<Pagination<DynamicformVo>>() {
			@Override
			public Pagination<DynamicformVo> call() throws Exception {
				return dynamicformService.queryForPage(queryVo);
			}
		};
	}

控制器代码2, 像这样写，正常处理没有报错，可惜不支持异步

/**
	 * 分页查询
	 * 
	 * @param queryVo
	 * @return　Pagination<DynamicformVo>
	 */
	@RequestMapping("queryPage")
	@ResponseBody
	public Pagination<DynamicformVo> getGrid(@ModelAttribute("DynamicformQueryVo") final DynamicformQueryVo queryVo) {
		return dynamicformService.queryForPage(queryVo);
	}

报错如下：

org.apache.shiro.UnavailableSecurityManagerException: No SecurityManager accessible to the calling code, either bound to the org.apache.shiro.util.ThreadContext or as a vm static singleton.  This is an invalid application configuration.
	at org.apache.shiro.SecurityUtils.getSecurityManager(SecurityUtils.java:123)
	at org.apache.shiro.subject.Subject$Builder.<init>(Subject.java:627)
	at org.apache.shiro.SecurityUtils.getSubject(SecurityUtils.java:56)
	at org.apache.shiro.web.servlet.ShiroHttpServletRequest.getSubject(ShiroHttpServletRequest.java:88)
	at org.apache.shiro.web.servlet.ShiroHttpServletRequest.getSubjectPrincipal(ShiroHttpServletRequest.java:93)
	at org.apache.shiro.web.servlet.ShiroHttpServletRequest.getUserPrincipal(ShiroHttpServletRequest.java:111)
	at org.springframework.web.servlet.FrameworkServlet.getUsernameForRequest(FrameworkServlet.java:1079)
	at org.springframework.web.servlet.FrameworkServlet.publishRequestHandledEvent(FrameworkServlet.java:1065)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:996)
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
	at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:659)
	at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:625)
	at org.apache.catalina.core.AsyncContextImpl$1.run(AsyncContextImpl.java:237)
	at org.apache.catalina.core.AsyncContextImpl.doInternalDispatch(AsyncContextImpl.java:380)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:215)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.asyncDispatch(CoyoteAdapter.java:299)
	at org.apache.coyote.http11.AbstractHttp11Processor.asyncDispatch(AbstractHttp11Processor.java:1632)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:599)
	at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2441)
	at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2430)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:619)

 如上所述，Shiro 在处理Servlet3异步请求时会出现异常？要怎么处理呢？可以通过log4j配置把该错误屏蔽掉，但这不是我想要的效果！

为啥redis的set类型存储超过一万条数据就会性能下降?

RT。

想过转化成字符串然后md5，怎奈两个json转换成字符串后，里面属性的顺序会变(比如第一个json里name在前age在后，第二个json有时就会age在前name在后)，这样的话明明是两个相同的json，字符串化以后验证的结果却是不相同的……

有没有什么方法能快速判断两个长json是否相同呢？

PS:尤其是对于golang而言，有没有什么更好的办法？

我在打印student上一步，初始化student的私有方法中对student进行了赋值，可上面主方法执行打印后student对象还是null，大佬们可知道为什么吗，感激不尽

以下为测试代码

7000w+简单key（key产生规则是笛卡尔积），vlaue基本就是1、2、3这种简单数字，怎么存比较省空间

加了悲观锁，

加了泄洪队列，

加了限流，

还会出现

如果发布文章时不需要分类，只需要提供关键词，当需要调用时，以关键词搜索，或者标题搜索、全文搜索方式返回即可。

提出此想法的原因是觉得让文章按栏目分类，创建栏目繁琐，而且还伴随二级、三级栏目，甚至无限分类等功能。

所以，我想以关键词取代栏目分类的想法不知可不可行，请大家指点哈！

Java小白求救，外观模式和命令模式有什么区别，它们都是把复杂逻辑屏蔽，只对外提供一个接口。具体要怎么分辨这两个模式呀！

听说mysql8比mysql5要快很多，我们就尝试将mysql从5.6升级到8.0,然后有些sql就变慢了

sql如下：

SELECT
   a.id AS 'id',
   CONCAT(a.firstname,' ',a.lastname) AS 'name',
   a.name AS fullName,
   a.firstname AS 'firstname',
   a.lastname AS 'lastname',
   a.teaching_style as teachingStyle,
   a.type_of_english as typeOfEnglish,
   a.avatar AS 'avatar',
   a.avatar_url AS 'avatarurl',
   c.course_id AS courseId,
   CONCAT(
   IFNULL(a.favorable_rate, '100'),
   '%'
   ) AS rate,
   f.file_path AS path
  FROM
  busi_teacher a
  LEFT JOIN busi_tea_schedule b  ON a.id = b.tea_id
  LEFT JOIN busi_tea_course c ON (a.id = c.tea_id AND c.issys = 1)
  LEFT JOIN busi_stu_course d ON b.stu_course = d.id
  LEFT JOIN busi_file f ON f.id = a.avatar
  WHERE   b. STATUS = 1
  AND b.can_normal = 1
  AND ( (a.is_fulltime = 1 AND b.is_contracted = 1) OR a.is_fulltime != 1 )
  AND b.ex_schedule_date > DATE_ADD(NOW(), INTERVAL 24 HOUR)
  AND (b.ex_schedule_date < '2019-12-25 08:00:00' OR b.ex_schedule_date > '2019-12-27 07:59:00')
  AND (b.ex_schedule_date < '2020-01-01 08:00:00' OR b.ex_schedule_date > '2020-01-02 07:59:00')
   AND a. STATUS IN (3, 7)
  AND b.del_flag = 0
  AND a.del_flag = 0
  AND a.isuse = 1
  AND (b.stu_course IS NULL OR d.course_status = 3)
  AND  FIND_IN_SET('152',c.course_id)
    AND HOUR(b.ex_schedule_date) < 21
    GROUP BY a.id
  ORDER BY b.is_contracted DESC, a.promoted DESC,(CASE a.is_fulltime WHEN 1 THEN 1 WHEN 0 THEN 2 ELSE 3 END),a.firstname
  LIMIT  10；

mysql版本5.6.16-log：执行0.157s,explain如下

mysql版本8.0.16：执行2.080s,explain如下

mysql8先执行a表，mysql5.6先执行b表。mysql8的Creating sort index花费了99%的时间，我将排序去掉后两个版本都执行一遍后，mysql8是要比mysql5.6要快，但是加上排序后mysql8就很慢了，感觉是在mysql8中排序并没有用到索引。有没有大神能看出来是哪儿出了问题吗，是mysql系统参数设置有问题吗？

我想对docker部署的mysql8.0.19进行备份，一开始试了一下Xtrabackup8.0.9 发现宿主机安装Xtrabackup不能连接到docker的mysql，需在docker容器里面安装。因为是微服务系统，数据库会有多个不想在每个容器中都安装Xtrabackup，请教各路大神宿主机安装Xtrabackup怎么对docker 容器的mysql备份，或者还有没有其它更好用的备份工具， mysqldump  这种方式不考虑

一下是允许命令后的异常信息

xtrabackup: recognized server arguments:--log_bin=mysql-bin--server-id=1--innodb_flush_log_at_trx_commit=1--innodb_log_buffer_size=1M--innodb_buffer_pool_size=64M--innodb_log_file_size=48M--innodb_autoextend_increment=64--innodb_open_files=300--innodb_file_per_table=1--innodb_checksum_algorithm=0--open_files_limit=4161xtrabackup: recognized client arguments:--user=root--password=*--host=172.17.0.2--port=8250--backup=1--parallel=4--target-dir=/home/back/db_cms_xtrabackupversion8.0.9basedonMySQLserver8.0.18Linux(x86_64)(revisionid:c5cbbe4)20031415:23:24version_checkConnectingtoMySQLserverwithDSN'dbi:mysql:;mysql_read_default_group=xtrabackup;host=172.17.0.2;port=8250'as'root'(usingpassword:YES).Failed to connect to MySQL server:DBIconnect(';mysql_read_default_group=xtrabackup;host=172.17.0.2;port=8250','root',...)failed:Can'tconnecttoMySQLserveron'172.17.0.2'(111)at-line1535.200314 15:23:24 Connecting to MySQL server host:172.17.0.2,user:root,password:set,port:8250,socket:notsetFailed to connect to MySQL server:Can'tconnecttoMySQLserveron'172.17.0.2'(111).

脚本

xtrabackup --defaults-file=/home/mysql/xxx/master/config/my.cnf -uroot -pXXX -Hlocalhost --port=8250 --backup --parallel=4 --target-dir=/home/back/db_xxx_ $name

 -H 一开始设置的是localhost不行，我换了mysql容器中的ip地址‘172.17.0.2’也不行。

之前有一个非maven项目是用spring，spring mvc，mybatis搭建的，我想能像spring boot那样，部署成可执行的jar包以微服务的方式进行部署安装，脱离单独tomcat软件。在eclipse中，这个怎么改动才能做到？

在分布式系统下，一个正常运行的系统，怎么解决大量的非法并发请求攻击。比如：有3~5万个非法的请求，同时请求系统的某些资源，这种情况该如何解决。还请各位大神指点一二！

有上图结构数据表，用PHP如何生成下面结构的JSON？

[

    {

        "name":"电脑",

        "id":"1",

        "list":[

            {

                "name":"无法开机",

                "id":"3"

            },

            {

                "name":"无法联网",

                "id":"4"

            },

            {

                "name":"蓝屏",

                "id":"5"

            }

        ]

    },

    {

        "name":"打印机",

        "id":"2",

        "list":[

            {

                "name":"卡纸",

                "id":"6"

            },

            {

                "name":"加粉",

                "id":"7"

            }

        ]

    }

]