[TOC] # 1. 会话及会话技术 ## 问题01：客户端存储和服务器存储的区别？   ## 问题02：如何写入和读取cookie？【记录历史访问者】  ### cookie的写入 ``` Cookie cookie = new Cookie("name","value"); response.addCookie(cookie); ``` > **void javax.servlet.http.HttpServletResponse.addCookie(Cookie cookie)** > Adds the specified cookie to the response. This method can be called multiple times to set more than one cookie. ### cookie的读取 ``` Cookie[] cookies = request.getCookies(); if(cookies!=null){ for(Cookie cookie:cookies){ String name = cookie.getName(); String value = cookie.getValue(); } } ``` > **Cookie[] javax.servlet.http.HttpServletRequest.getCookies()** > Returns **an array** containing all of the Cookie **objects** the client sent with this request. This method **returns null if no cookies were sent**. > **String javax.servlet.http.Cookie.getName()** > Returns the name of the cookie. The name **cannot be changed after creation**. > **String javax.servlet.http.Cookie.getValue()** > Returns the value of the cookie. > **void javax.servlet.http.Cookie.setValue(String newValue)** > Assigns **a new value** to a cookie after the cookie is created. With Version 0 cookies, values **should not contain** white space, brackets, parentheses, equals signs, commas, double quotes, slashes, question marks, at signs, colons, and semicolons. Empty values may not behave the same way on all browsers. > **(不支持特殊字符及中文)** ## 问题03：服务器存储对象有哪些？page、request、session、application |对象名称|所属类型|范围| | -- | -- | -- | |page| java.lang.Object | page| |request | javax.servlet.http.HttpServletRequest | request | |session | javax.servlet.http.HttpSession |session | | application | javax.servlet.ServletContext | application | > 为什么需要域对象？ * [ ] MVC各个模块之间需要进行相互通信，特别是JSP与Servlet、JSP与JSP、Servlet与Servlet之间 ## 问题04：为什么需要这么多存储对象？ * [ ] 适用于不同场景 * [ ] 因为request作用域太小 * [ ] 一般我们使用session，因为application作用域太大 ## 问题05：这些存储对象有什么区别？ |对象名称|特点|应用场景| | -- | -- | -- | | page| 只在当前页面有效 | 除当前页面需要立即显示数据，一般不使用 | | request | 只在当前请求有效，即相同request | 除请求转发时，一般不使用 | | session | 一次会话有效，即没有与服务器断开连接 | 最常使用，非所有用户共享数据结皆能存储 | | application | 整个服务器运行期间有效，所有用户共享 | 一般用于保存服务器配置信息，通常不使用 | ## 问题06：如何进行信息的增删改查？  > **void javax.servlet.ServletRequest.setAttribute(String name, Object o)** > **Stores an attribute** in this request. **Attributes are reset** between requests. This method is most often used in conjunction with RequestDispatcher. Attribute **names** should follow **the same conventions as package names**. If the object passed in is **null**, the effect is the same as calling **removeAttribute**. --- > **void javax.servlet.ServletRequest.removeAttribute(String name)** > **Removes** an attribute from this request. --- > **Object javax.servlet.ServletRequest.getAttribute(String name)** > Returns the value of the named attribute **as an Object**, or **null** if **no** attribute of the given name **exists**. > 注意：getAttribute()因为得到的值为null或object，因此可能引发**空指针异常**或者**类型转换异常** ## 问题07：通过request如何获得其他存储对象？  > **HttpSession javax.servlet.http.HttpServletRequest.getSession(boolean create)** > Returns **the current HttpSession** associated with this request or, if there is **no current session** and **create is true**, returns **a new session**. If **create is false** and the request has no valid HttpSession, this method returns **null**. > **HttpSession javax.servlet.http.HttpServletRequest.getSession()** > Returns the current session associated with this request, or if the request does **not have a session, creates one**. ## 问题08：为什么不直接使用session和application，而是需要从request中得到？ * [ ] 因为在Servlet中没有内置对象，在Service方法（运行方法）中只有request参数作为的对象 ## 问题09：如何销毁session或使session中的某一个特殊标记失效？ 1. 删除session中的属性 ``` session.removeAttribute("key"); ``` 2. 使用空串覆盖session中的属性 ``` session.setAttribute("key",""); ``` 3. 设置session快速过期  ``` session.setMaxInactiveInterval​(1); ``` * [ ] 服务器统一设置过期时间 ``` <session-config> <session-timeout>min</session-timeout> </session-config> ``` 4. 使session立即失效  ``` session.invalidate(); ``` # 2. 其他内置对象page/pageContext/config/exception |对象名称|所属类型|范围| | -- | -- | -- | | page | javax.servlet.jsp.HttpJspPage | page | | pageContext |javax.servlet.jsp.PageContext | page| | config |javax.servlet.ServletConfig | page| | exception|java.lang.Throwable | page| ## 问题10：pageContext有什么作用？ * [ ] 获得其他内置对象，特别是request * [ ] ``` ${pageContext.request.ContextPath} ```  ## 问题11：是否每个JSP都有Exception对象？ * [ ] 并不是 * [ ] 只有设置isErrorPage="true"才有内置对象exception  ## 问题12：九个内置对象分别属于什么对象？即内置对象分类。 1. 错误对象：exception 2. servlet对象：page、config 3. 输入输出对象：request、response、out 4. 通信对象：session、application、pageContext