[TOC]  # 1. out[javax.servlet.jsp.JspWriter] ## 问题01：如何使用out对象向网页中输出内容？  ## 问题02：JspWriter对象和PrintWriter对象有什么区别？   ## 问题03：如何解决JspWriter输出顺序与代码不一致的问题？ > **设置缓冲区为0kb**  # 2. request[javax.servlet.http.HttpServletRequest] | 分类 | 功能 | 应用 | | --- | --- | --- | | 行信息 | 获取请求行（方式、协议、请求URI）| 限制请求方式和协议、转换相对路径| | 头信息 | 获取请求头（客户端IP、referer）| 限制请求客户端、实现防盗链| | 主体 | 获取请求参数|获得单个值或者多个请求参数传递的值（单个、多个） | | 编码 | 设置请求编码| 防止请求参数的值发生乱码【重要】（post乱码、get乱码）| | 视图跳转 | 请求转发| 将请求递交给下一个视图，继续进行处理（请求转发、相对**web应用**路径）| ## 问题04：如何获取请求行信息？如何限制请求方式？ * [ ] getMethod() 获得客户端向服务器端传送数据的方法，如get，post * [ ] getProtocol()获得客户端向服务器端传送数据所依据的协议名称   ## 问题05：如何转换相对路径？ ``` String path = request.getContextPath(); ``` > Returns the portion of the request URI that indicates **the context of the request**. The context path always **comes first** in a request URI. The path **starts with** a "/" character but **does not end with** a "/" character.  > **注意：得到的路径最后没有"/"，需要手动添加。** ## 问题06：如何获得其他头信息？ * [ ] getHeader(String name) 获得HTTP协议定义的文件头信息 * [ ] getRemoteAddr()获取客户端的IP地址 * [ ] getServerPort() 获取服务器的端口号  ## 问题07：如何实现防盗链？   ## 问题08：如何获得请求参数？ ``` String username = request.getParameter("username"); ``` Returns the value of a request parameter as a **String**, or **null** if the parameter does **not exist**. You should only use this method when you are sure the parameter **has only one value**. If the parameter might have **more than one value**, use **getParameterValues**(java.lang.String). ``` String[] users = request.getParameterValues("user"); ``` Returns **an array of String objects** containing all of the values the given request parameter has, or null if the parameter does not exist. If the parameter has **a single value**, the array has **a length of 1**.  > 数组的显示可以使用：<%=Arrays.toString(字符串数组)%> ## 问题09：如何解决请求乱码？ * [ ] GET提交乱码 ``` String username = request.getParameter("username"); username = new String(username.getBytes("ISO8859-1"),"UTF-8"); ``` * [ ] POST提交乱码  ``` request.setCharacterEncoding("utf-8"); ``` > Overrides the name of the character encoding used in the body of this request. This method must be called **prior** to **reading request parameters** or **reading input** using getReader(). ## 问题10：如何进行视图跳转（请求转发）？ ``` request.getRequestDispatcher("URL").forward(request, response); ``` > Returns a RequestDispatcher object that acts as a wrapper for **the resource located at the given path**. The pathname specified **may be relative**, although it **cannot** extend **outside the current servlet context**. If the path **begins with a "/"** it isinterpreted as relative to the **current context root**. > Forwards a request from a servlet **to another resource** (servlet, JSP file, or HTML file) on the server. This method allows one servlet **to do preliminary processing** of a request and **another resource to generate the response. **forward** should be called before the response has been committed** to the client (before response body output has been flushed). If the response already has been committed, this method throws an IllegalStateException.  # 3. response[javax.servlet.http.HttpServletResponse] | 分类 | 功能 | 应用 | | --- | --- | --- | | 行信息 | 设置响应行（状态码）| 设置正确状态码、设置异常状态码| | 头信息 |设置响应头（refresh、禁止缓存） | 可以实现自动刷新和跳转、实现禁止缓存| | 主体 | 获取out并输出内容|获取out对象，输出内容print、append | | 编码 | 设置响应编码| 设置响应内容类型以及编码（通过header设置、直接设置）| | 视图跳转 | 重定向|定向到其他视图（重定向、相对**服务器**路径）| ## 问题11：如何设置响应状态码？显示错误消息页面 * [ ] setStatus(int status)  > **void javax.servlet.http.HttpServletResponse.setStatus(int sc)** > **Sets the status code** for this response. This method is used to set the return status code when **there is no error** (for example, for the status codes SC_OK or SC_MOVED_TEMPORARILY). If **there is an error**, and the caller wishes to **invoke an error-page** defined in the web application, the **sendError** method should be used instead. ## 问题12：如何手动唤醒错误处理页面？   ## 问题13：如何实现网页自动跳转或刷新？ * [ ] setHeader    ``` response.setHeader("refresh", "5;url='http://www.pzhu.cn'"); ``` ## 问题14：如何实现网页禁止缓存？ ``` response.setHeader("Pragma", "No-cache"); response.setHeader("Cache-Control", "no-cache"); response.setDateHeader("Expires", 0); ``` ## 问题15：如何使用response实现输出内容？ ``` response.getWriter().print(""); ```  ## 问题16：如何解决响应内容出现乱码？ ``` response.setCharacterEncoding("UTF-8"); ```  ## 问题17：为什么设置了编码，前端页面还是乱码？尝试切换浏览器编码？ > **void javax.servlet.ServletResponse.setCharacterEncoding(String charset)** > **In the case of HTTP**, the character encoding is communicated **as part of the Content-Type header** for text media types. Note that the character encoding **cannot be communicated** via HTTP headers if **the servlet does not specify a content type**; however, it is still used to encode text written via the servlet response's writer.  > **void javax.servlet.ServletResponse.setCharacterEncoding(String charset)** **【解决办法】** > **Sets the character encoding (MIME charset)** of the response being sent tothe client, for example, to UTF-8. If the character encoding has already been set by setContentType or setLocale, this method overrides it. Calling **setContentType** with the String of **text/html** and calling **this method** with the String of **UTF-8** is equivalent withcalling **setContentType** with the String of **text/html; charset=UTF-8**. > This method can be called repeatedly to change the character encoding.This method has **no effect** if it is called **after getWriter** has been called or after **the response has been committed**.  ## 问题18：如何实现重定向？ ``` response.sendRedirect("URL"); ``` > Sends a temporary **redirect** response to the client using the specified redirect location **URL**. This method can **accept relative URLs**; the servlet container must convert the relative URL to an absolute URL before sending the response to the client. If the location is relative **without a leading '/'** the container interprets it as relative to **the current request URI**. If the location is relative **with a leading '/' the** container interprets it as relative to **the servlet container root**.  * [ ] 注意：多次重定向可能产生以下异常  ## 问题19：请求转发和重定向有什么区别？  优点：可以转到服务器内部路径或不可直接访问路径，隐藏目标资源路径。 缺点：可能发生相对路径错误。 * [ ] 程序发生异常唤醒错误页面也是属于请求转发的一种 * [ ] 当在错误页面存在相对路径时就可能出现异常