[TOC]  # 1. out[javax.servlet.jsp.JspWriter] ## 問題01：如何使用out對象向網頁中輸出內容？  ## 問題02：JspWriter對象和PrintWriter對象有什么區別？   ## 問題03：如何解決JspWriter輸出順序與代碼不一致的問題？ > **設置緩沖區為0kb**  # 2. request[javax.servlet.http.HttpServletRequest] | 分類 | 功能 | 應用 | | --- | --- | --- | | 行信息 | 獲取請求行（方式、協議、請求URI）| 限制請求方式和協議、轉換相對路徑| | 頭信息 | 獲取請求頭（客戶端IP、referer）| 限制請求客戶端、實現防盜鏈| | 主體 | 獲取請求參數|獲得單個值或者多個請求參數傳遞的值（單個、多個） | | 編碼 | 設置請求編碼| 防止請求參數的值發生亂碼【重要】（post亂碼、get亂碼）| | 視圖跳轉 | 請求轉發| 將請求遞交給下一個視圖，繼續進行處理（請求轉發、相對**web應用**路徑）| ## 問題04：如何獲取請求行信息？如何限制請求方式？ * [ ] getMethod() 獲得客戶端向服務器端傳送數據的方法，如get，post * [ ] getProtocol()獲得客戶端向服務器端傳送數據所依據的協議名稱   ## 問題05：如何轉換相對路徑？ ``` 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：得到的路徑最后沒有"/"，需要手動添加。** ## 問題06：如何獲得其他頭信息？ * [ ] getHeader(String name) 獲得HTTP協議定義的文件頭信息 * [ ] getRemoteAddr()獲取客戶端的IP地址 * [ ] getServerPort() 獲取服務器的端口號  ## 問題07：如何實現防盜鏈？   ## 問題08：如何獲得請求參數？ ``` 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**.  > 數組的顯示可以使用：<%=Arrays.toString(字符串數組)%> ## 問題09：如何解決請求亂碼？ * [ ] GET提交亂碼 ``` String username = request.getParameter("username"); username = new String(username.getBytes("ISO8859-1"),"UTF-8"); ``` * [ ] POST提交亂碼  ``` 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(). ## 問題10：如何進行視圖跳轉（請求轉發）？ ``` 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] | 分類 | 功能 | 應用 | | --- | --- | --- | | 行信息 | 設置響應行（狀態碼）| 設置正確狀態碼、設置異常狀態碼| | 頭信息 |設置響應頭（refresh、禁止緩存） | 可以實現自動刷新和跳轉、實現禁止緩存| | 主體 | 獲取out并輸出內容|獲取out對象，輸出內容print、append | | 編碼 | 設置響應編碼| 設置響應內容類型以及編碼（通過header設置、直接設置）| | 視圖跳轉 | 重定向|定向到其他視圖（重定向、相對**服務器**路徑）| ## 問題11：如何設置響應狀態碼？顯示錯誤消息頁面 * [ ] 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. ## 問題12：如何手動喚醒錯誤處理頁面？   ## 問題13：如何實現網頁自動跳轉或刷新？ * [ ] setHeader    ``` response.setHeader("refresh", "5;url='http://www.pzhu.cn'"); ``` ## 問題14：如何實現網頁禁止緩存？ ``` response.setHeader("Pragma", "No-cache"); response.setHeader("Cache-Control", "no-cache"); response.setDateHeader("Expires", 0); ``` ## 問題15：如何使用response實現輸出內容？ ``` response.getWriter().print(""); ```  ## 問題16：如何解決響應內容出現亂碼？ ``` response.setCharacterEncoding("UTF-8"); ```  ## 問題17：為什么設置了編碼，前端頁面還是亂碼？嘗試切換瀏覽器編碼？ > **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)** **【解決辦法】** > **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**.  ## 問題18：如何實現重定向？ ``` 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：多次重定向可能產生以下異常  ## 問題19：請求轉發和重定向有什么區別？  優點：可以轉到服務器內部路徑或不可直接訪問路徑，隱藏目標資源路徑。 缺點：可能發生相對路徑錯誤。 * [ ] 程序發生異常喚醒錯誤頁面也是屬于請求轉發的一種 * [ ] 當在錯誤頁面存在相對路徑時就可能出現異常