把实现了Servlet接口的Java程序叫做，Servlet
Servlet接口Sun公司有两个默认的实现类：HttpServlet，
1.构建一个普通的Maven项目，删除里面的src目录，以后学习就在这个项目里面建立Moduel；这个空的工程就是Maven的主工程；
2.关于Maven父子工程的理解：
父项目中有
<modules> <module>servlet-01</module> </modules>子项目中有
<parent> <artifactId>javaweb-02-servlet</artifactId> <groupId>com.kuang</groupId> <version>1.0-SNAPSHOT</version> </parent>父项目中jar(java) 子项目可以直接使用
son extends father3.Maven环境优化 1.修改web.xml为最新的 2.将maven的结构搭建完整
4.编写一个Servlet程序 1.编写一个普通类 2.实现Servlet接口
public class HelloServlet extends HttpServlet{ //由于get post只是 请求 实现的不同的方式，可以相互调用，业务逻辑一样 @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("进入了doGet方法"); // ServletOutputStream outputStream = resp.getOutputStream(); PrintWriter writer = resp.getWriter(); writer.print("Hello,Servlet"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); } }5.编写Servlert的映射 为什么需要映射：我们写的是JAVA程序，但是要通过浏览器访问，而浏览器需要连接web服务器，所以我们需在web服务器中注册我们写的Servlert，还需给他一个浏览器能够访问的路径；
<!--注册Servlet--> <servlet> <servlet-name>hello</servlet-name> <servlet-class>com.kuang.servlet.HelloServlet</servlet-class> </servlet> <!--Servlet的请求路径--> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping>6.配置Tomcat 注意：配置项目发布的路径就可以了
7.启动测试，ok！
Servlet是有Web服务器调用，web服务器在收浏览器请求之后，会：
一个Servlet可以指定一个映射路径
<servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping>一个Servlet可以指定多个映射路径
<servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello2</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello3</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello4</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello5</url-pattern> </servlet-mapping>一个Servlet可以指定通用映射路径
<servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello/*</url-pattern> </servlet-mapping>默认请求路径
<servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping>指定一些后缀或者前缀等等…
<!--可以自定义后缀实现请求映射, (注意点*前面不能加项目映射的路径)--> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>*.shuai</url-pattern> </servlet-mapping>优先级问题 指定了固有的映射路径优先级最高，如果找不到就会走默认的处理请求
<servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello/*</url-pattern> </servlet-mapping> <!--404--> <servlet> <servlet-name>error</servlet-name> <servlet-class>com.kuang.servlet.ErrorServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>error</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping> <!-- 服务器开始运行或者输入其他不存在的映射就会到404,如果输入/hello 会进入hello-->web容器在启动的时候，它会为每个web程序都创建一个对应的ServletContext对象，它代表了当前web应用；
我在这个servlet中保存的数据，可以在另外一个servlet中拿到；
public class HelloServlet extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // this.getInitParameter() 初始化参数 // this.getServletConfig() Servlet配置 // this.getServletContext() Servlet上下文 ServletContext servletContext = this.getServletContext(); String username = "帅哥"; //数据 servletContext.setAttribute("username",username); //将一个数据保存在了ServletContext中，名字为：username。值 username System.out.println("hello"); } } public class GetServlet extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { ServletContext servletContext = this.getServletContext(); String username = (String) servletContext.getAttribute("username"); resp.setContentType("text/html"); resp.setCharacterEncoding("utf-8"); resp.getWriter().print("名字"+username); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }测试访问结果；
Properties
在java目录下新建properties在resources目录下新建properties发现：都被打包到了同一个路径下：classes，我们俗称这个路径为calsspath： 思路：需要一个文件流
aa.properties:
username=root21312321 password=12czxcasd public class ServletDemo05 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/kuang/servlet/aa.properties"); Properties prop = new Properties(); prop.load(is); String username = prop.getProperty("username"); String password = prop.getProperty("password"); resp.getWriter().print(username+":"+password); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }访问测试即可；
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，代表响应的一个HttpServletResponse；
如果要获取客户端请求过来的参数：找HttpServletRequest如果要给客户端响应一些信息：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);响应状态码
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;3.验证码功能
@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //如何让浏览器3秒自动刷新一次； 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.blue); 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(); for (int i = 0; i < 7 - num.length(); i++) { sb.append("0"); } num = sb.toString() + num; return num; } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); }4.实现重定向 一个web资源（B）收到客户端（A）请求后，B他会通知A客户端去访问另一个web资源（C），这个过程叫重定向
常见场景：
用户登录 void sendRedirect(String var1) throws IOEception;测试：
@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { /* resp.setHeader("Location","/r/img"); resp.setStatus(302); */ resp.sendRedirect("/r/img");//重定向 }面试题：请你聊聊重定向和转发的区别？ 相同点
页面都会实现跳转不同点
请求转发的时候，url不会产生变化重定向会后，url地址栏会发生变化 引入 @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); //重定向时候一定要注意，路径问题，否则404 resp.sendRedirect("/r/success.jsp"); } index.jsp <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> success.jsp <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <h1>success</h1> </body> </html>HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，Http请求中所有信息会被封装到HttpServletRequest，通过这个HttpServletRequest的方法，获得客户端所有信息
获取前端传递的参数，请求转发
@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("utf-8"); resp.setCharacterEncoding("utf-8"); String username = req.getParameter("username"); String password = req.getParameter("password"); String[] hobbys = req.getParameterValues("hobbys"); System.out.println("========================="); //后台接收中文乱码问题 System.out.println(username); System.out.println(password); System.out.println(Arrays.toString(hobbys)); System.out.println("========================="); req.getRequestDispatcher("success.jsp").forward(req,resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req,resp); }面试题：请你聊聊重定向和转发的区别？ 相同点
页面都会实现跳转不同点
请求转发的时候，url不会产生变化 307重定向会后，url地址栏会发生变化 302