6Servlet

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Servlet

1、Servlet简介

  • Servlet就是sun公司开发动态web的一门技术
  • Servlet就是一个接口，开发一个Servlet小程序，只需完成两个小步骤：
    • 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

2、Servlet创建步骤

Servlet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，在项目里面建立Moudel；

2.Maven环境优化

​ 1.修改web.xml

<?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_3_1.xsd"
         version="3.1"
         metadata-complete="true">

</web-app>

​ 2.将maven的结构搭建完整

3.编写一个Servlet程序

​ 1.编写一个普通类

​ 2.实现Servlet接口，直接继承HttpServlet；

public class HelloServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //ServletOutputStream outputStream = resp.getOutputStream();
        PrintWriter writer = resp.getWriter();
        writer.println("Hello,Servlet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
        //响应的类型：html
        response.setContentType("text/html");
		//设置编码格式
        response.setCharacterEncoding("utf-8");
        //获取响应的输出流
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Hello World!</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Hello World!</h1>");
        out.println("</body>");
        out.println("</html>");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

4.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，使用我们需要在web服务中注册我们写的Servlet，还需给它一个浏览器能够访问的路径；

<!-- 注册Servlet -->
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.cc.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>

5.配置Tomcat

6.启动测试

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：

image-20210606150010241

4、Mapping问题

1.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；

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；

image-20210606230905456

5.1、共享数据

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 = "提莫";
        context.setAttribute("username",username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

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.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        resp.getWriter().print("名字是：" + username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

<servlet>
        <servlet-name>Hello</servlet-name>
        <servlet-class>com.cc.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    
    <servlet>
        <servlet-name>getcontext</servlet-name>
        <servlet-class>com.cc.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getcontext</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>

注意：要先访问hello把数据存进去，在访问getc来读取数据

执行结果：

image-20210606230633374

5.2、获取初始化参数

public class ServletDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().print(url);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

<context-param>        <param-name>url</param-name>        <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>    </context-param>

<servlet>        <servlet-name>getInitParameter</servlet-name>        <servlet-class>com.cc.servlet.ServletDemo03</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>getInitParameter</servlet-name>        <url-pattern>/getip</url-pattern>    </servlet-mapping>

执行结果：

image-20210606232419688

5.3、请求转发

image-20210607104558890

public class ServletDemo04 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        ServletContext context = this.getServletContext();        context.getRequestDispatcher("/getip").forward(req,resp);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        doPost(req, resp);    }}

<servlet>        <servlet-name>getDispatcher</servlet-name>        <servlet-class>com.cc.servlet.ServletDemo04</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>getDispatcher</servlet-name>        <url-pattern>/getdp</url-pattern>    </servlet-mapping>

执行结果：

image-20210606234208263

5.4、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；

maven由于它的约定大于配置，之后可能遇到我们写的配置文件，无法被导出或者生效的问题，解决方案：

<build>        <resources>            <resource>                <directory>src/main/resources</directory>                <includes>                    <include>**/*.properties</include>                    <include>**/*.xml</include>                </includes>                <filtering>true</filtering>            </resource>            <resource>                <directory>src/main/java</directory>                <includes>                    <include>**/*.properties</include>                    <include>**/*.xml</include>                </includes>                <filtering>true</filtering>            </resource>        </resources>    </build>

思路：需要一个文件流；

username=cccpassword=casascsa

public class ServletDemo05 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        //InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/cc/servlet/aa.properties");        Properties prop = new Properties();        prop.load(is);        String username = prop.getProperty("username");        String password = prop.getProperty("password");        resp.setContentType("text/html");        resp.setCharacterEncoding("utf-8");        resp.getWriter().print(username + "：" + password);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        doPost(req, resp);    }}

<servlet>        <servlet-name>getProperties</servlet-name>        <servlet-class>com.cc.servlet.ServletDemo05</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>getProperties</servlet-name>        <url-pattern>/getpt</url-pattern>    </servlet-mapping>

image-20210607123235353

执行结果：

image-20210607123300384

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

6.1、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);void setStatus(int var1);

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;

6.2、下载文件

1.向浏览器输出消息

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（Content-Disposition）下载我们需要的东西 attachment;filename= 以附件的形式下载

​ 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buffer缓冲区，使用OutputStream将缓冲区中的数据输出到客户端

​ 8.关闭流

public class FileServlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        //1.要获取下载文件的路径        String realPath = "E:\\\\JavaProjects\\\\javaweb-02-servlet\\\\resp\\\\src\\\\main\\\\resources\\\\多多.png";        //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  attachment;filename= 以附件的形式下载        resp.setHeader("Content-Disposition","attachment;filename=" + URLEncoder.encode(fileName,"utf-8"));		//4.获取下载文件的输入流        FileInputStream fis = new FileInputStream(realPath);		//5.创建缓冲区        int len = 0;        byte[] buffer = new byte[1024];        //6.获取OutputStream对象        ServletOutputStream sos = 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 = fis.read(buffer)) > 0) {            sos.write(buffer,0,len);        }        //8.关闭流        fis.close();        sos.close();    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        doPost(req, resp);    }}

<servlet>    <servlet-name>filedown</servlet-name>    <servlet-class>com.cc.servlet.FileServlet</servlet-class>  </servlet>  <!-- Servlet的请求路径 -->  <servlet-mapping>    <servlet-name>filedown</servlet-name>    <url-pattern>/down</url-pattern>  </servlet-mapping>

执行结果：

image-20210607173353210

6.3、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

    //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   getGraphics（笔）        Graphics2D g = (Graphics2D) image.getGraphics();        //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/jpg");        //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

Random创建随机类

StringBuffer

private String makeNum() {        Random r = new Random();        String num = r.nextInt(9999999) + "";        StringBuffer sb = new StringBuffer();        for ( int i = 0; i < 7 - num.length(); i++ ) {            sb.append("0");        }        num = sb.toString() + num;        return num;    }

执行效果：

image-20210608114454593

6.4、实现重定向

image-20210608114720917

一个web资源收到客户端请求后，它会通知客户端区访问另外一个web资源，这个过程叫重定向

void sendRedirect(String var1) throws IOException;

@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {    //resp.setHeader("Location","/resp/img");    //resp.setStatus(302);    //重定向    resp.sendRedirect("/resp/img");}

执行结果：

image-20210608163519909

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；
  • 重定向的时候，url地址栏会发生变化；

${pageContext.request.contextPath} 代表当前项目

JSP页面第一句一定要加下面的，不然会乱码

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

提交信息页面：

<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>

Servlet：

@Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        //处理请求        String username = req.getParameter("username");        String password = req.getParameter("password");        System.out.println(username + "：" + password);        resp.setCharacterEncoding("utf-8");        resp.setContentType("text/html");        //重定向        resp.sendRedirect("/resp/success.jsp");    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        doGet(req, resp);    }

重定向的页面：

<%@ page contentType="text/html;charset=UTF-8" language="java" %><html><head>    <title>Title</title></head><body>    <h1>Success!</h1></body></html>

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HttpServletRequest的方法，获得客户端的所有信息；

7.1、获取前端传递的参数

image-20210608193825794

7.2、请求转发

index：

<%@ page contentType="text/html;charset=UTF-8" language="java" %><html><head>    <title>登录</title></head><body><h1>个人信息登录</h1><div>    <form action="${pageContext.request.contextPath}/login" method="post">        用户名：<input type="text" name="username"> <br>        密码：<input type="password" name="password"> <br>        爱好：            <input type="checkbox" name="hobbys" value="代码">代码            <input type="checkbox" name="hobbys" value="健身">健身            <input type="checkbox" name="hobbys" value="打游戏">打游戏        <br>        <input type="submit">    </form></div></body></html>

Servlet：

@Overrideprotected 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("--------------");    System.out.println(username);    System.out.println(password);    System.out.println(Arrays.toString(hobbys));    System.out.println("--------------");    //请求转发    req.getRequestDispatcher("/success.jsp").forward(req,resp);}

success：

<%@ page contentType="text/html;charset=UTF-8" language="java" %><html><head>    <title>登录成功页面</title></head><body><h1>恭喜你，登录成功！</h1></body></html>

登录界面：

image-20210608202419202

登录成功界面：

image-20210608202452832

IDEA输出界面：

image-20210608202525521

8、总结

request大多数都是get方法，只有唯一一个set方法（用来设置编码语言）

image-20210608203127345

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