Servlet知識總結(6)——HttpServletResponse
阿新 • • 發佈:2020-08-07
6.HttpServletResponse
web伺服器接收到客戶端的HTTP請求,針對這個請求,分別建立一個代表請求的HttpServletRequest物件和一個代表響應的HttpServletResponse物件;
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如果要獲取客戶端請求過來的引數:找HttpServletRequest
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如果要給客戶響應一些資訊:找HttpServletResponse
1.簡單分類
負責向瀏覽器傳送資料的方法
ServletOutputStream getOutputStream() throws IOException; PrintWriter getWriter() throws IOException;
負責向瀏覽器傳送響應頭的方法
void setCharacterEncoding(String var1); void setContentLength(int var1); void setContentLengthLong(long var1); void setContentType(String var1); void setDateHeader(String var1, long var2); void addDateHeader(String var1, long var2); void setHeader(String var1, String var2); void addHeader(String var1, String var2); void setIntHeader(String var1, int var2); void addIntHeader(String var1, int var2);
響應的狀態碼
int SC_CONTINUE = 100; int SC_SWITCHING_PROTOCOLS = 101; int SC_OK = 200; int SC_CREATED = 201; int SC_ACCEPTED = 202; int SC_NON_AUTHORITATIVE_INFORMATION = 203; int SC_NO_CONTENT = 204; int SC_RESET_CONTENT = 205; int SC_PARTIAL_CONTENT = 206; int SC_MULTIPLE_CHOICES = 300; int SC_MOVED_PERMANENTLY = 301; int SC_MOVED_TEMPORARILY = 302; int SC_FOUND = 302; int SC_SEE_OTHER = 303; int SC_NOT_MODIFIED = 304; int SC_USE_PROXY = 305; int SC_TEMPORARY_REDIRECT = 307; int SC_BAD_REQUEST = 400; int SC_UNAUTHORIZED = 401; int SC_PAYMENT_REQUIRED = 402; int SC_FORBIDDEN = 403; int SC_NOT_FOUND = 404; int SC_METHOD_NOT_ALLOWED = 405; int SC_NOT_ACCEPTABLE = 406; int SC_PROXY_AUTHENTICATION_REQUIRED = 407; int SC_REQUEST_TIMEOUT = 408; int SC_CONFLICT = 409; int SC_GONE = 410; int SC_LENGTH_REQUIRED = 411; int SC_PRECONDITION_FAILED = 412; int SC_REQUEST_ENTITY_TOO_LARGE = 413; int SC_REQUEST_URI_TOO_LONG = 414; int SC_UNSUPPORTED_MEDIA_TYPE = 415; int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416; int SC_EXPECTATION_FAILED = 417; int SC_INTERNAL_SERVER_ERROR = 500; int SC_NOT_IMPLEMENTED = 501; int SC_BAD_GATEWAY = 502; int SC_SERVICE_UNAVAILABLE = 503; int SC_GATEWAY_TIMEOUT = 504; int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
2.下載檔案
- 向瀏覽器輸出資訊
- 下載檔案
- 要獲取下載檔案的路徑
- 下載檔名
- 設定讓瀏覽器能夠支援下載我們需要的東西
- 獲取下載檔案的輸出流
- 建立緩衝區
- 獲取OutputStream物件
- 將FileOutputStream流寫入到buffer緩衝區,使用OutputStream將緩衝區的資料輸出到客戶端
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//1. 要獲取下載檔案的路徑
String realPath = "D:\\code\\javaweb-02-servlet\\response\\src\\main\\resources\\1.png";
System.out.println("下載檔案的路徑:" + realPath);
//2. 下載檔名
String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
//3. 設定想辦法讓瀏覽器能夠支援(Content-Disposition)下載我們需要的東西,中文檔名URLEncoder.encode編碼,否則有可能亂碼
resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"utf-8"));
//4. 獲取下載檔案的輸出流
FileInputStream in = new FileInputStream(realPath);
//5. 建立緩衝區
int len = 0;
byte[] buffer = new byte[1024];
//6. 獲取OutputStream物件
ServletOutputStream out = resp.getOutputStream();
//7. 將FileOutputStream流寫入到buffer緩衝區,使用OutputStream將緩衝區的資料輸出到客戶端
while ((len = in.read(buffer))!=-1){
out.write(buffer,0,len);
}
in.close();
out.close();
}
3.驗證碼功能
驗證怎麼來的?
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前端實現
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後端實現,需要用到java的圖片類,生成一個圖片
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//如何讓瀏覽器3秒鐘重新整理一次
resp.setHeader("refresh","3");
//在記憶體中建立一個圖片
BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
//得到圖片
Graphics2D g = (Graphics2D) image.getGraphics();//筆
//設定圖片的背景顏色
g.setColor(Color.white);
g.fillRect(0,0,80,20);
//給圖片寫資料
g.setColor(Color.cyan);
g.setFont(new Font(null,Font.BOLD,20));
g.drawString(makeNum(),0,20);
//告訴瀏覽器,這個請求用圖片的方式開啟
resp.setContentType("image/jpeg");
//網站存在快取,不讓瀏覽器快取
resp.setDateHeader("expires",-1);
resp.setHeader("Cache-Control","no-cache");
resp.setHeader("Pragma","no-cache");
//把圖片寫給瀏覽器
ImageIO.write(image,"jpg",resp.getOutputStream());
}
//生成隨機數
private String makeNum(){
Random random = new Random();
String num = random.nextInt(9999999) + "";
StringBuffer sb = new StringBuffer();
//確保產生的是七位數
for (int i = 0; i < 7-num.length(); i++) {
sb.append("0");
}
num = sb.toString() + num;
return num;
}
4.實現重定向
什麼是重定向?
一個web資源收到客戶端請求後,會通知客戶端去訪問另外一個web資源,這個過程叫做重定向
常見場景:
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使用者登入
void sendRedirect(String var1) throws IOException;
測試:
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.sendRedirect("/re/img");//重定向
}
面試題:請說說重定向和轉發的區別?
相同點:
- 頁面都會實現跳轉
不同點:
- 請求轉發時,url不會發生變化
- 重定向時,url會發生變化
5.簡單實現登入重定向
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<h2>Hello World!</h2>
<%--這裡提交的路徑,需要尋找到專案的路徑--%>
<%--${pageContext.request.contextPath}代表當前的專案--%>
<form action="${pageContext.request.contextPath}/login" method="get">
使用者名稱:<input type="text" name="username"><br>
密碼:<input type="password" name="password"><br>
<input type="submit">
</form>
</body>
</html>
public class RedirectDemo extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String username = req.getParameter("username");
String password = req.getParameter("password");
System.out.println(username + ":" + password);
resp.sendRedirect("/re/Success.jsp");
}
<servlet>
<servlet-name>Redirect</servlet-name>
<servlet-class>com.shida.response.RedirectDemo</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Redirect</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1>success</h1>
</body>
</html>