有效沟通问答-【官方】百战程序员_IT在线教育培训机构

会员可以在此提问，百战程序员老师有问必答

对大家有帮助的问答会被标记为“推荐”
看完课程过来浏览一下别人提的问题，会帮你学得更全面

截止目前，同学们一共提了 132441个问题

时间排序推荐排序

老师，我想问一下，为什么commission_pct转换为字符串，小数点前的0没有呢？

select last_name, nvl(to_char(commission_pct, '9.99'), 'no commission') from employees

JAVA 全系列/第三阶段：数据库编程/SQL 语言 32056楼

请求URL为“/abc/a.do”,Servlet能映射到 /abc 吗？

JAVA 全系列/第五阶段：JavaWeb开发/Servlet技术详解（旧） 32057楼

老师，我用的pycharm，我没有找到Database的按键。

Python 全系列/第八阶段：轻量级Web开发利器-Flask框架/Flask数据库 32058楼

class zidingyi:
    '''自定义异常raise'''
    def __init__(self,shuzi):
        Exception.__init__(self)
        self.shuzi=shuzi
   
    def __str__(self):
        return str(self.shuzi)+",年龄错误,应在1-150之间"

if __name__=="__main__":
    age=int(input("请输入你的年龄："))
    if (age<1 or age>150):
        raise zidingyi(age)
    else:
        print("正常的年龄",age)

Exception这行为什么会报错？

Python 全系列/第二阶段：Python 深入与提高/异常机制 32059楼

老师，我这个没问题啊，为什么导入不了啊。我试了很多次

Python 全系列/第二阶段：Python 深入与提高/模块 32060楼

老师，我的idea到期了怎么破解，Evaluate for free点不了

JAVA 全系列/第一阶段：JAVA 快速入门/飞机大战小项目训练 32061楼

import multiprocessing
import time


def func1(conn1):
    sub_info="Hello!"
    print(f"进程1--{multiprocessing.current_process().pid} 发送参数{sub_info}")
    time.sleep(1)
    conn1.send(sub_info)
    print(f"来自线程2:{conn1.recv()}")
    time.sleep(1)

def func2(conn2):
    sub_info="你好！"
    print(f"进程2--{multiprocessing.current_process().pid} 发送参数{sub_info}")
    time.sleep(1)
    conn2.send(sub_info)
    print(f"来自线程1：{conn2.recv()}")
    time.sleep(1)



if __name__ == '__main__':
    #创建管道
    conn1,conn2=multiprocessing.Pipe()
    #创建子进程
    process1=multiprocessing.Process(target=func1,args=("conn1",))
    process2=multiprocessing.Process(target=func2,args=("func2",))
    #启动进程
    process1.start()
    process2.start()

进程2--59024发送参数你好！

进程1--51220发送参数Hello!

Process Process-2:

Process Process-1:

Traceback (most recent call last):

File "D:\Anaconda\anaconda3\envs\python\lib\multiprocessing\process.py", line 315, in _bootstrap

self.run()

File "D:\Anaconda\anaconda3\envs\python\lib\multiprocessing\process.py", line 108, in run

self._target(*self._args, **self._kwargs)

File "D:\Pycharm\python学习\python系统化学习\网络与并发编程\Pipe实现进程间的通信.py", line 9, in func1

conn1.send(sub_info)

File "D:\Anaconda\anaconda3\envs\python\lib\multiprocessing\process.py", line 315, in _bootstrap

self.run()

File "D:\Anaconda\anaconda3\envs\python\lib\multiprocessing\process.py", line 108, in run

self._target(*self._args, **self._kwargs)

AttributeError: 'str' object has no attribute 'send'

File "D:\Pycharm\python学习\python系统化学习\网络与并发编程\Pipe实现进程间的通信.py", line 17, in func2

conn2.send(sub_info)

AttributeError: 'str' object has no attribute 'send'

这个哪里错了呢

Python 全系列/第三阶段：Python 网络与并发编程/并发编程 32062楼

单例模式不可或缺的是什么，__new__起到什么作用

Python 全系列/第一阶段：Python入门/面向对象 32063楼

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

JAVA 全系列/第五阶段：JavaWeb开发/Servlet技术详解（旧） 32064楼

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？

人工智能/第九阶段：机器学习-概率图模型（旧）/CRF算法 32065楼

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?

JAVA 全系列/第六阶段：项目管理与SSM框架/SpringMVC 32066楼

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();
    }
}

JAVA 全系列/第五阶段：JavaWeb开发/Servlet技术详解（旧） 32067楼

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

JAVA 全系列/第十三阶段：分布式文件存储与数据缓存/Nginx 32068楼

老师这个报错是什么意思，密码不对么，，，，，

Python 全系列/第五阶段：数据库编程/mysql的使用 32069楼

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？

JAVA 全系列/第二阶段：JAVA 基础深化和提高/IO 流技术（旧） 32070楼

同学您好