Servlet
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接口的的Java程序叫做，Servlet
2、HelloServlet
Servlet接口在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>子项目中会有：
<parent>
<artifactId>javaweb-02-servlet</artifactId>
<groupId>com.jiang</groupId>
<version>1.0-SNAPSHOT</version>
</parent>父项目中的java子项目可以直接使用
son extends father3.Maven环境优化
- 修改web.xml为最新的
- 将Maven的结构搭建完整
4.编写一个Servlet程序
3.package com.jiang.servlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
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();
writer.println("Hello,Servlet");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doPost(req, resp);
}
}
5.编写一个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，所以我们需要在web服务中注册我们写的Servlet，还需要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.jiang.servlet.HelloServlet</servlet-class>
</servlet>
<!--Servlet的请求路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/jiang</url-pattern>
</servlet-mapping>
</web-app>6.配置Tomcat
注意：配置项目发布的路径就可以了
7.启动测试，成功
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：
4、Mapping问题
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的请求路径--> <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>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>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 例如：hello/asdasdas.java --> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>*.java</url-pattern> </servlet-mapping>请求默认路径
<servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/*</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> <servlet-name>error</servlet-name> <servlet-class>com.jiang.servlet.ErrorServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>error</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping>package com.jiang.servlet; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter; public class ErrorServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.setCharacterEncoding("utf-8"); resp.setContentType("text/html"); PrintWriter writer = resp.getWriter(); writer.println("<h1>404</h1>"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); } }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；
5.1、共享数据
1、在这个Servlet中保存的数据，可以在另外一个servlet中拿到；
package com.jiang;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
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
}
}
2、写另外一个Servlet
package com.jiang;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;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);
}
}
3、注册Servlet
<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>测试访问结果；
- 没走hello之前，请求getc为：名字null
- 走了一遍hello，再请求getc为：名字姜嘉航
5.2、获取初始化参数
1、在web.xml配置一些web应用初始化参数
<!--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>2、编写获取初始化参数的Servlet
package com.jiang;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
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 {
doGet(req, resp);
}
}
3、注册Servlet
<servlet>
<servlet-name>gp</servlet-name>
<servlet-class>com.jiang.ServletDemo03</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>gp</servlet-name>
<url-pattern>/gp</url-pattern>
</servlet-mapping>测试：
5.3、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);
}原理图：
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:
思路：需要一个文件流；
1、在resources目录下创建一个db.properties
username=root
password=123456public class ServletDemo05 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/jiang/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);
}
}
访问测试即可ok；
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);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
- 向浏览器输出消息
- 下载文件
- 要获取下载文件的路径
- 下载的文件名是啥？
- 设置想办法让浏览器能够支持下载我们需要的东西
- 获取下载文件的输入流
- 创建缓冲区
- 获取OutputStream对象
- 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！
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// 1. 要获取下载文件的路径
String realPath = "D:\\图片\\1.png";
System.out.println("下载文件的路径："+realPath);
// 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();
}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，生产一个图片
package com.kuang.servlet;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
public class ImageServlet 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);
}
}
6.4、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；
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>
@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);
//重定向时候一定要注意，路径问题，否则404；
resp.sendRedirect("/r/success.jsp");
}
<servlet>
<servlet-name>requset</servlet-name>
<servlet-class>com.kuang.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>
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
@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("=============================");
System.out.println(req.getContextPath());
//通过请求转发
//这里的 / 代表当前的web应用
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