javaweb
6、Servlet
6.1、Servlet简介
- Servlet就是sun公司开发动态web的一门技术
- sun公司在这些API中提供了一个接口叫做: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
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,以后我们的学习就在这个项目里建立module;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>org.example</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
父项目中的java子项目可以直接用
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.println("hello,servlet");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
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,所以我们需要在web服务器中注册我们写的servlet,还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.lc.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
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>
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
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
5.指定一个后缀或者前缀等等....
<!--注意点:*.前面不能加项目映射路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>*.liang</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:
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Sercvlet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="梁聪"; //数据
servletContext.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 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 {
}
}
<servlet>
<servlet-name>HelloServlet</servlet-name>
<servlet-class>com.lc.servlet.HelloServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>GetServlet</servlet-name>
<servlet-class>com.lc.servlet.GetServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloServlet</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>GetServlet</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 servletContext = this.getServletContext();
String url = servletContext.getInitParameter("url");
resp.getWriter().print(url);
}
3、请求转发
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
System.out.println("进入了ServletDemo02");
//RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/gp");//转发的请求路径
//requestDispatcher.forward(req,resp);//调用forward实现请求转发;
servletContext.getRequestDispatcher("/gp").forward(req,resp);
}
4、读取资源文件
Properties
- 在java目录下新建properties
- 在resource目录下新建properties
如果遇到配置文件无法导出或者生效,解决方案:
<!--在build中配置resource,来防止我们资源导出失败的问题-->
<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>
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 ServletDemo03 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/lc/servlet/db.properties");
Properties prop = new Properties();
prop.load(is);
String user = prop.getProperty("username");
String paw = prop.getProperty("password");
resp.getWriter().print(user+":"+paw);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
访问测试即可。
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
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
@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:\\IdeaProjects\\java-web-servlet\\src\\main\\resources\\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
resp.setHeader("Content-Disposition","attachment;fileName="+fileName);
// 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
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,生成一个图片
package com.lc.servlet;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;
@WebServlet("/image")
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//如何让浏览器3秒刷新一次
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.BLUE);
g.fillRect(0,0,80,20);
//给图片写数据
g.setColor(Color.BLACK);
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");
}
String s = sb.toString() + num;
return num;
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
4、实现重定向
常见场景:
- 用户登录
void sendRedirect(String var1) throws IOException;
测试:
@WebServlet("/red")
public class RedirectServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/*
resp.setHeader("location","/r/image");
resp.setStatus(302);
*/
String name=req.getContextPath();
System.out.println(name);
resp.sendRedirect(name+"/image")//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不会发生变化; 307
- 重定向的时候,url地址栏会发生变化; 302
<html>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<body>
<h2>Hello World!</h2>
<%--这里提交的路径,需要找到项目的路径--%>
<form action="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>
@WebServlet("/login")
public class RequestTest extends HttpServlet {
@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);
resp.sendRedirect(req.getContextPath()+"/success.jsp");
}
<%@ 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。
1、获取前端传递的参数
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>登录</title>
</head>
<body>
<h1>登录</h1>
<div style="text-align: center">
<form action="login" method="get">
用户名:<input type="text" name="username"> <br>
密码:<input type="password" name="password"> <br>
爱好:
<input type="checkbox" name="hobby" value="女孩">女孩
<input type="checkbox" name="hobby" value="唱歌">唱歌
<input type="checkbox" name="hobby" value="代码">代码
<input type="checkbox" name="hobby" value="电影">电影
<br>
<input type="submit">
</form>
</div>
</body>
</html>
@WebServlet("/login")
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String username = req.getParameter("username");
String password = req.getParameter("password");
String[] hobbies = req.getParameterValues("hobby");
System.out.println("-----------------------------------------------------------");
System.out.println(username);
System.out.println(password);
System.out.println(Arrays.toString(hobbies));
System.out.println("-----------------------------------------------------------");
//通过请求转发
req.getRequestDispatcher("success.jsp").forward(req,resp);
}
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1> 登录成功 </h1>
</body>
</html>