JavaWeb-6Servlet

6、Servlet

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

\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：

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>

\3. 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>

\4. 默认请求路径

<!--默认请求路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/*</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 {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletContext context = this.getServletContext();//this.getInitParameter() 初始化参数// this.getServletConfig() Servlet配置// this.getServletContext() Servlet上下文String username = "epfox";context.setAttribute("username", username);}
}

public class GetServlet extends HttpServlet {@Overrideprotected 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);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

  <servlet><servlet-name>hello</servlet-name><servlet-class>com.epfox.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.epfox.servlet.GetServlet</servlet-class></servlet><servlet-mapping><servlet-name>getc</servlet-name><url-pattern>/getc</url-pattern></servlet-mapping>

测试访问结果;

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>

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

3、请求转发

    @Overrideprotected 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forword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;

username=root
password=123456

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

访问测试即可ok;

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buffer缓冲区

\8. 使用OutputStream将缓冲区中的数据输出到客户端!

public class FileServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String realPath = "/Users/maby/IdeaProjects/javaweb-03-servlet/response/src/main/resources/微信.png";System.out.println("下载文件的路径:" + realPath);String fileName = realPath.substring(realPath.lastIndexOf("/") + 1);resp.setHeader("Content-Disposition", "attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));FileInputStream in = new FileInputStream(realPath);int len = 0;byte[] buffer = new byte[1024];ServletOutputStream out = resp.getOutputStream();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 ImageServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {resp.setHeader("refresh","3");BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);Graphics2D g = (Graphics2D) image.getGraphics();g.setColor(Color.white);g.fillRect(0,0,80,20);g.setColor(Color.BLUE);g.setFont(new Font(null,Font.BOLD,20));g.drawString(makeNum(),0,20);resp.setContentType("image/jpeg");resp.setDateHeader("expires",-1);resp.setHeader("Cache-Control","no-cache");resp.setHeader("pragma","no-cache");ImageIO.write(image,"jpg",resp.getOutputStream());}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;}

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

1 void sendRedirect(Stringvar1) throws IOException;

测试:

public class RedirectServlet extends HttpServlet {@Overrideprotected 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;

5、简单实现登录重定向

<%--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 RequestTest extends HttpServlet {@Overrideprotected 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("/r/success.jsp");}

  <servlet><servlet-name>requset</servlet-name><servlet-class>com.epfox.servlet.RequestTest</servlet-class></servlet><servlet-mapping><servlet-name>requset</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>

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;

获取参数，请求转发

public class LoginServlet extends HttpServlet {@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("====================");System.out.println(req.getContextPath());req.getRequestDispatcher("/success.jsp").forward(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
重定向时候，url地址栏会发生变化; 302