6.1、Servlet简介
Servlet就是sun公司开发动态web的一门技术
Sun在这些API中提供一个接口叫做:Servlet,如果你想开发一个Servlet程序,只需要完成两个小
步骤:
编写一个类,实现Servlet接口
把开发好的Java类部署到web服务器中。
把实现了Servlet接口的Java程序叫做,Servlet
6.2、HelloServlet
Serlvet接口Sun公司有两个默认的实现类:HttpServlet,GenericServlet
1. 构建一个普通的Maven项目,删掉里面的src目录,以后我们的学习就在这个项目里面建立
Moudel;这个空的工程就是Maven主工程;
2. 关于Maven父子工程的理解:
父项目中会有
<modules>
<module>servlet-01</module>
</modules>
子项目会有
<parent> <artifactId>javaweb-02-servlet</artifactId>
<groupId>com.kuang</groupId>
<version>1.0-SNAPSHOT</version> </parent>
父项目中的java子项目可以直接使用
son extends father
3. Maven环境优化
1. 修改web.xml为最新的
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0"
metadata-complete="true">
</web-app>
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,这里我们直接继承HttpServlet
public class HelloServlet extends HttpServlet {
//由于get或者post只是请求实现的不同的方式,可以相互调用,业务逻辑都一样;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//ServletOutputStream outputStream = resp.getOutputStream();
PrintWriter writer = resp.getWriter();
//响应流 writer.print("Hello,Serlvet");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
} }
5. 编写Servlet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,
所以我们需要再web服务中注册我们写的Servlet,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!
6.3、Servlet原理
Servlet是由Web服务器调用,web服务器在收到浏览器请求之后,会:

1.浏览器向服务器发出GET请求(请求服务器ServletA)
2.服务器上的容器逻辑接收到该url,根据该url判断为Servlet请求,此时容器逻辑将产生两个对象:请求对象(HttpServletRequest)和响应对象(HttpServletResponce)
3.容器逻辑根据url找到目标Servlet(本示例目标Servlet为ServletA),且创建一个线程A
4.容器逻辑将刚才创建的请求对象和响应对象传递给线程A
5.容器逻辑调用Servlet的service()方法
6.service()方法根据请求类型(本示例为GET请求)调用doGet()(本示例调用doGet())或doPost()方法
7.doGet()执行完后,将结果返回给容器逻辑
8.线程A被销毁或被放在线程池中
6.4、Mapping问题
1. 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>
2. 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>
5. 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 hello/sajdlkajda.qinjiang --> <servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>*.qinjiang</url-pattern>
</servlet-mapping>
6. 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;
<!--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>
6.5、ServletContext
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,它代表了当前的
web应用;
1、共享数据
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 context = this.getServletContext();
String username = "秦疆"; //数据
context.setAttribute("username", username);
// 将一个数据保存在了 ServletContext中,名字为:username 。值 username } }
}
}
public class GetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
String username = (String) context.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); }
}
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.kuang.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>getc</servlet-name>
<servlet-class>com.kuang.servlet.GetServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>getc</servlet-name>
<url-pattern>/getc</url-pattern>
</servlet-mapping>
2、获取初始化参数
<!--配置一些web应用初始化参数-->
<context-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
</context-param>
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
String url = context.getInitParameter("url");
resp.getWriter().print(url);
}
3、请求转发
@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
System.out.println("进入了ServletDemo04");
//RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp");
//转发的请求路径
//requestDispatcher.forward(req,resp);
//调用forward实现请求转发;
context.getRequestDispatcher("/gp").forward(req,resp); }
4、读取资源文件
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classpath:
思路:需要一个文件流;
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 user = prop.getProperty("username");
String pwd = prop.getProperty("password");
resp.getWriter().print(user + ":" + pwd);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp); }
}
6.6、HttpServletResponse
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
1、简单分类
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;
2、下载文件
1. 向浏览器输出消息 (一直在讲,就不说了)
2. 下载文件
1. 要获取下载文件的路径
2. 下载的文件名是啥?
3. 设置想办法让浏览器能够支持下载我们需要的东西
4. 获取下载文件的输入流
5. 创建缓冲区
6. 获取OutputStream对象
7. 将FileOutputStream流写入到buffffer缓冲区
8. 使用OutputStream将缓冲区中的数据输出到客户端!
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String realPath = "D:\\MySoft\\apache-maven-3.6.1\\conf\\settings.xml";
// 1. 要获取下载文件的路径 String realPath = "F:\\班级管理\\西开【19525】\\2、代码\\JavaWeb\\javaweb- 02-servlet\\response\\target\\classes\\秦疆.png";
// System.out.println("下载文件的路径:"+realPath); 12345
// 2. 下载的文件名是啥?
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. 获取下载文件的输入流
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将缓冲区中的数据 输出到客户端!
while ((len = in.read(buffer)) > 0) {
out.write(buffer, 0, len);
}
in.close();
out.close();
}
}
3、验证码功能
验证怎么来的?
前端实现
后端实现,需要用到 Java 的图片类,生产一个图片
public class QRCodeStudy extends HttpServlet {
@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

B一个web资源收到客户端A请求后,B他会通知A客户端去访问另外一个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 IOException;
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
重定向时候,url地址栏会发生变化;

<%--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>
public class RequestServlet extends HttpServlet {
//由于get或者post只是请求实现的不同的方式,可以相互调用,业务逻辑都一样;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入了请求");
String username = req.getParameter("username");
String password = req.getParameter("password");
resp.sendRedirect("/s/success.jsp");
}
<servlet>
<servlet-name>login</servlet-name>
<servlet-class>com.doublew.servlet.RequestServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
<html>
<body>
<h2>success</h2>
</body>
</html>
6.7、HttpServletRequest
HttpServletRequest代表客户端的请求,用户通过Http协议访问服务器,HTTP请求中的所有信息会被封
装到HttpServletRequest,通过这个HttpServletRequest的方法,获得客户端的所有信息;

public class LoginServlet extends HttpServlet {
//由于get或者post只是请求实现的不同的方式,可以相互调用,业务逻辑都一样;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setCharacterEncoding("utf-8");
System.out.println("进入了请求");
String username = req.getParameter("username");
String password = req.getParameter("password");
String[] hobbys = req.getParameterValues("hobbys");
System.out.println(username);
System.out.println(password);
System.out.println(hobbys.toString());
//req.getRequestDispatcher(req.getContextPath()+"/"+"success.jsp").forward(req,resp);
//通过请求转发
//这里的 / 代表当前的web应用
req.getRequestDispatcher("/success.jsp").forward(req,resp);
//resp.sendRedirect("/s/success.jsp");
}