单例模式不可或缺的是什么，__new__起到什么作用
老师，我学的比较晚，下载的版本比较新，想问一下这几个目录是干嘛的呢，点开后都是这样的
老师好，alpha0存储的是t时刻到达每个label的概率，alpha1存储的是从哪个label到达当前时刻的label，这样理解的对吗？如果是这样的话，alpha1存储的是行索引，就转移前的位置，对吗？
user.getUsername().length()<=0
我想不明白这个判断的理由是啥,如果一个user对象不是null的话,那么它在什么情况下会是username的长度是0呢?
使用xml文件配置网页报500错误是咋回事，老师能帮忙看看嘛
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0" metadata-complete="false"> <context-param> <param-name>key1</param-name> <param-value>BJSXT</param-value> </context-param> <context-param> <param-name>key2</param-name> <param-value>BJSXT</param-value> </context-param> <servlet> <servlet-name>demoServlet</servlet-name> <servlet-class>com.example.demo.DemoServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>demoServlet</servlet-name> <url-pattern>/demo.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>getRequestDataServlet</servlet-name> <servlet-class>com.example.demo.GetRequestDataServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>getRequestDataServlet</servlet-name> <url-pattern>/getinfo.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>getRequestHeaderServlet</servlet-name> <servlet-class>com.example.demo.GetRequestHeaderServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>getRequestHeaderServlet</servlet-name> <url-pattern>/getHeader.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>LanguageServlet</servlet-name> <servlet-class>com.example.demo.LanguageServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LanguageServlet</servlet-name> <url-pattern>/Languages.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>RespByteServlet</servlet-name> <servlet-class>com.example.demo.RespByteServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>RespByteServlet</servlet-name> <url-pattern>/RespByte.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>RedirectServlet</servlet-name> <servlet-class>com.example.demo.RedirectServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>RedirectServlet</servlet-name> <url-pattern>/Redirect.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>DownFileServlet</servlet-name> <servlet-class>com.example.demo.DownFileServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>DownFileServlet</servlet-name> <url-pattern>/Down.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>GetBaseInfoServlet</servlet-name> <servlet-class>com.example.demo.GetBaseInfoServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>GetBaseInfoServlet</servlet-name> <url-pattern>/getBaseInfo.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>ContextReadInfoServlet</servlet-name> <servlet-class>com.example.demo.ContextReadInfoServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>ContextReadInfoServlet</servlet-name> <url-pattern>/Context.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>GlobalContainerServlet</servlet-name> <servlet-class>com.example.demo.GlobalContainerServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>GlobalContainerServlet</servlet-name> <url-pattern>/Global.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>GetConfigInfoServlet</servlet-name> <servlet-class>com.example.demo.GetConfigInfoServlet</servlet-class> <init-param> <param-name>key1</param-name> <param-value>BJSXT</param-value> </init-param> <init-param> <param-name>key2</param-name> <param-value>ITBZ</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>GetConfigInfoServlet</servlet-name> <url-pattern>/Config.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>CreatCookieSrvlet</servlet-name> <servlet-class>com.example.demo.CreatCookieSrvlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>CreatCookieSrvlet</servlet-name> <url-pattern>/Cookie.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>GetCookieDataServlet</servlet-name> <servlet-class>com.example.demo.GetCookieDataServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>GetCookieDataServlet</servlet-name> <url-pattern>/GetCookie.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>WelcomeServlet</servlet-name> <servlet-class>com.example.demo.WelcomeServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>WelcomeServlet</servlet-name> <url-pattern>/Welcome.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>CreateHttpSessionServlet</servlet-name> <servlet-class>com.example.demo.CreateHttpSessionServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>CreateHttpSessionServlet</servlet-name> <url-pattern>/CreatSession.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>GetHttpSessionDataServlet</servlet-name> <servlet-class>com.example.demo.GetHttpSessionDataServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>GetHttpSessionDataServlet</servlet-name> <url-pattern>/GetSessionData.do</url-pattern> </servlet-mapping> <session-config> <session-timeout>1</session-timeout> </session-config> <servlet> <servlet-name>WelcomeSessionServlet</servlet-name> <servlet-class>com.example.demo.WelcomeSessionServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>WelcomeSessionServlet</servlet-name> <url-pattern>/WelcomeSession.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>AutoStartServlet</servlet-name> <servlet-class>com.example.demo.AutoStartServlet</servlet-class> <init-param> <param-name>path</param-name> <param-value>image</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>AutoStartServlet</servlet-name> <url-pattern>/auto.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>ThreadSafeServlet</servlet-name> <servlet-class>com.example.demo.ThreadSafeServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>ThreadSafeServlet</servlet-name> <url-pattern>/Safe.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>FileUploadServlet</servlet-name> <servlet-class>com.example.demo.FileUploadServlet</servlet-class> <multipart-config> <file-size-threshold>2000</file-size-threshold> </multipart-config> </servlet> <servlet-mapping> <servlet-name>FileUploadServlet</servlet-name> <url-pattern>/fileupload.do</url-pattern> </servlet-mapping> </web-app>
package com.example.demo; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.Part; import java.io.IOException; import java.io.PrintWriter; import java.util.UUID; public class FileUploadServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("utf-8"); String desc = req.getParameter("desc"); Part part=req.getPart("file"); // InputStream inputStream = part.getInputStream(); String filename= UUID.randomUUID().toString()+part.getSubmittedFileName().substring(part.getSubmittedFileName().lastIndexOf(".")); ServletContext servletContext = this.getServletContext(); String realPath = servletContext.getRealPath("image"+filename); part.write(realPath); PrintWriter out=resp.getWriter(); out .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">"); out.println("<HTML>"); out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>"); out.println(" <BODY>"); out.println("上传成功"); out.println("</BODY>"); out.println("</HTML>"); out.flush(); out.close(); } }
麻烦老师看一下我这哪里有问题吗？我单独访问nginx和tomcat都没有问题
老师这个报错是什么意思，密码不对么，，，，，
老师，这种输入输出的形式和创建Scanner对象的输入方式有什么不同呢？
老师你好，去settings搜索enco后，无论打什么代码都会出现这样的错误，是什么东西没调过来吗？
这是咋回事？ Xshell连不上虚拟机，但虚拟机好好的，而且也能ping得通，经常这样，连不上的时候只能重启电脑就又可以连上了
lass Employee: def __init__(self,name,salary): self.name = name self.__salary = salary def salary(self): print("薪资是：",self.__salary) return self.__salary emp1 = Employee("王小丫",50000) emp1.salary()
老师我想问一下，salary在第一个def构造法下已经被私有化了，但是在第二个def下仍然可以被调用出来。是说print理解为是一种外部操作，而调用这种是内部操作，所以虽然私有了，但还可以调用。谢谢
<style> .box { width: 300px; height: 300px; } .left { float: left; width: 150px; height: 150px; } .top { float: top; width: 150px; height: 150px; background-color: skyblue; } .bottom { float: bottom; width: 150px; height: 150px; background-color: pink; } .right { float: right; width: 150px; height: 300px; background-color: blue; } </style> </head> <body> <div class="box"> <div class="left"> <div class="top"></div> <div class="bottom"></div> </div> <div class="right"></div> </div> </body>
老师您好，我这里没有Unicode 怎么办。我想知道一下为什么我没有
<style> div>h3{ color:red;} </style> <body> <div> <h3>这是一个标题</h3> <p> <h3>这是一个标题</h3> </p> </div> </body>
老师，在第一次启动网络的时候是启动成功的，后来关掉之后在打开就变成这样了。这是什么问题呢？
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