标签：如何 lock 需要 second apache apach -o doc https
web服务器接收到客户端的HTTP请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象和一个代表响应的HttpServletResponse对象；
如果要获取客户端请求过来的参数：找HttpServletRequest
如果要给客户响应一些信息：找HttpServletResponse
负责向浏览器发送数据的方法
ServletOutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;
负责向浏览器发送响应头的方法
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);
响应的状态码
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;
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//1. 要获取下载文件的路径
String realPath = "D:\\code\\javaweb-02-servlet\\response\\src\\main\\resources\\1.png";
System.out.println("下载文件的路径：" + realPath);
//2. 下载文件名
String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
//3. 设置想办法让浏览器能够支持(Content-Disposition)下载我们需要的东西,中文文件名URLEncoder.encode编码，否则有可能乱码
resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"utf-8"));
//4. 获取下载文件的输出流
FileInputStream in = new FileInputStream(realPath);
//5. 创建缓冲区
int len = 0;
byte[] buffer = new byte[1024];
//6. 获取OutputStream对象
ServletOutputStream out = resp.getOutputStream();
//7. 将FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区的数据输出到客户端
while ((len = in.read(buffer))!=-1){
out.write(buffer,0,len);
}
in.close();
out.close();
}
验证怎么来的？
前端实现
后端实现，需要用到java的图片类，生成一个图片
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//如何让浏览器3秒钟刷新一次
resp.setHeader("refresh","3");
//在内存中创建一个图片
BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
//得到图片
Graphics2D g = (Graphics2D) image.getGraphics();//笔
//设置图片的背景颜色
g.setColor(Color.white);
g.fillRect(0,0,80,20);
//给图片写数据
g.setColor(Color.cyan);
g.setFont(new Font(null,Font.BOLD,20));
g.drawString(makeNum(),0,20);
//告诉浏览器，这个请求用图片的方式打开
resp.setContentType("image/jpeg");
//网站存在缓存，不让浏览器缓存
resp.setDateHeader("expires",-1);
resp.setHeader("Cache-Control","no-cache");
resp.setHeader("Pragma","no-cache");
//把图片写给浏览器
ImageIO.write(image,"jpg",resp.getOutputStream());
}
//生成随机数
private String makeNum(){
Random random = new Random();
String num = random.nextInt(9999999) + "";
StringBuffer sb = new StringBuffer();
//确保产生的是七位数
for (int i = 0; i < 7-num.length(); i++) {
sb.append("0");
}
num = sb.toString() + num;
return num;
}
什么是重定向？
一个web资源收到客户端请求后，会通知客户端去访问另外一个web资源，这个过程叫做重定向
常见场景：
用户登录
void sendRedirect(String var1) throws IOException;
测试：
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.sendRedirect("/re/img");//重定向
}
面试题：请说说重定向和转发的区别？
相同点：
- 页面都会实现跳转
不同点：
- 请求转发时，url不会发生变化
- 重定向时，url会发生变化
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<h2>Hello World!</h2>
<%--这里提交的路径，需要寻找到项目的路径--%>
<%--${pageContext.request.contextPath}代表当前的项目--%>
<form action="${pageContext.request.contextPath}/login" method="get">
用户名：<input type="text" name="username"><br>
密码：<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>
标签：如何 lock 需要 second apache apach -o doc https
原文地址：https://www.cnblogs.com/apachecn/p/13448207.html
