Java(JavaWeb02)
参考视频:8. HelloServlet(狂神)
6. Servlet
6.1 Servlet简介
- servlet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
对于Servlet接口,sun公司有两个默认的实现类:HttpServlet、GenericServlet
- 构建一个普通的Maven项目,并删掉src目录,以后在这个项目里建立Module。这个空的工程就是Maven的主工程。
- pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.zach</groupId>
<artifactId>javaweb-02-servlet</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
</properties>
<dependencies>
<!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>4.0.1</version>
<scope>provided</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
<dependency>
<groupId>javax.servlet.jsp</groupId>
<artifactId>javax.servlet.jsp-api</artifactId>
<version>2.3.3</version>
<scope>provided</scope>
</dependency>
</dependencies>
</project>
- 关于Maven父子工程的理解:
- 父项目的pox.xml中会有
<modules>
<module>servlet-01</module>
</modules>
- 子项目的pox.xml中会有
<parent>
<groupId>com.zach</groupId>
<artifactId>javaweb-02-servlet</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
- 父项目中的jar包,子项目可以直接使用。
son extends father
关于parent标签问题:
- 问题1: 没有自动生成parent标签,是因为配置与版本等问题。
- 解决方法:在maven文件夹下的conf下的settings.xml的profiles标签里添加下面配置:
<profile>
<id>jdk-1.8</id>
<activation>
<activeByDefault>true</activeByDefault>
<jdk>1.8</jdk>
</activation>
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
</properties>
</profile>
-
问题2: 自动生成parent标签后,几秒就消失了。原因是被“替换中”出现了问题,属于IDEA软件的bug范畴。更新版本可修复。如果因为某种原因无法使用新版本,只能手动操作。
-
官方问答:https://intellij-support.jetbrains.com/hc/en-us/community/posts/4406369605266/comments/4406387494162
-
解决方法(手动):改成如下即可
-
关于问题2的截图展示:
-
刚开始生成,有parent标签
-
生成完全结束后,没有parent标签
- Maven环境优化
- 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>
- 将maven的结构搭建完整
- 编写一个Servlet程序
- 编写一个普通类,实现Servlet接口,这里我们直接继承HttpServlet
package com.zach.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 {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// super.doGet(req, resp);
// 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 {
// super.doPost(req, resp);
doGet(req, resp);
}
}
- 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服务中注册我们写的Servlet,还需要给它一个浏览器能够访问的路径。
- 在web.xml中增加配置如下:
<!--注册Servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.zach.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>
- 配置Tomcat
- 注意配置项目发布的路径:
/s1
- 启动测试
- Output乱码问题:
-Dfile.encoding=utf-8
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
- 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-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>
- 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>
- 默认请求路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
- 指定一些后缀或者前缀等
<!--可以自定义后缀实现请求映射
注意:*前面不能加项目映射的路径以及/-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>*.sj</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 才会走默认的处理请求。
<!--404-->
<servlet>
<servlet-name>error</servlet-name>
<servlet-class>com.zach.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。
6.5.1 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。
package com.zach.servlet;
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 = "柴客";//数据
context.setAttribute("username",username);//将一个数据保存在了ServletContext中
}
}
package com.zach.servlet;
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().println("你的名字:"+username);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- 测试访问结果:
- 进入HelloServlet前,先进入GetServlet:
你的名字:null
- 进入HelloServlet后,再进入GetServlet:
你的名字:柴客
- 进入HelloServlet前,先进入GetServlet:
6.5.2 获取初始化参数
- web.xml
<!--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>
- ServletDemo03
package com.zach.servlet;
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().println(url);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
6.5.3 请求转发
package com.zach.servlet;
import javax.servlet.RequestDispatcher;
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 ServletDemo04 extends HttpServlet {
@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);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
6.5.4 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,我们称为
classpath
- 如果打包后target里没有,在pom.xml添加以下配置。
<!--在build中配置resources,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>false</filtering>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>false</filtering>
</resource>
</resources>
</build>
- 思路:需要一个文件流!
username=rootroot
password=123456123456
package com.zach.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.InputStream;
import java.util.Properties;
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/zach/servlet/aa.properties");
Properties prop = new Properties();
prop.load(is);
String userName = prop.getProperty("username");
String passWord = prop.getProperty("password");
resp.getWriter().println(userName+"\n"+passWord);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- 访问测试即可。
6.6 HttpServletResponse
- 响应
- 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,一个代表响应的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
6.6.1 简单分类
- 负责向浏览器发送数据的方法
public ServletOutputStream getOutputStream() throws IOException;
public PrintWriter getWriter() throws IOException;
- 负责向浏览器发送响应头的方法
public void setCharacterEncoding(String charset);
public void setContentLength(int len);
public void setContentLengthLong(long len);
public void setContentType(String type);
public void setDateHeader(String name, long date);
public void addDateHeader(String name, long date);
public void setHeader(String name, String value);
public void addHeader(String name, String value);
public void setIntHeader(String name, int value);
public void addIntHeader(String name, int value);
- 响应的状态码(常见)
/**
* Status code (200) indicating the request succeeded normally.
*/
public static final int SC_OK = 200;
/**
* Status code (302) indicating that the resource has temporarily
* moved to another location, but that future references should
* still use the original URI to access the resource.
*
* This definition is being retained for backwards compatibility.
* SC_FOUND is now the preferred definition.
*/
public static final int SC_MOVED_TEMPORARILY = 302;
/**
* Status code (404) indicating that the requested resource is not
* available.
*/
public static final int SC_NOT_FOUND = 404;
/**
* Status code (500) indicating an error inside the HTTP server
* which prevented it from fulfilling the request.
*/
public static final int SC_INTERNAL_SERVER_ERROR = 500;
/**
* Status code (502) indicating that the HTTP server received an
* invalid response from a server it consulted when acting as a
* proxy or gateway.
*/
public static final int SC_BAD_GATEWAY = 502;
6.6.2 下载文件
-
向浏览器输出消息(前面一直在讲,此处省略)
-
下载文件
- 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都支持我们下载的东西。文件名是中文的时候,可以设置
URLEncoder.encode(fileName, "UTF-8")
,否则有可能乱码 - 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!
- FileServlet
package com.zach.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.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
// 下载文件
public class FileServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// 1. 获取下载文件的路径
String realPath = "C:\\Users\\Administrator\\IdeaProjects\\JavaWeb\\javaweb-02-servlet\\response\\src\\main\\resources\\柴客.png";
System.out.println("要下载的文件的路径:"+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都支持我们下载的东西。文件名是中文的时候,可以设置`URLEncoder.encode(fileName, "UTF-8")`,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();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
6.6.3 验证码功能
- 验证码怎么来的?
- 前端实现
- 后端实现,需要用到java图片类,生成一个图片
- ImageServlet
package com.zach.servlet;
import sun.awt.image.BufferedImageDevice;
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秒刷新一次(自动)
resp.setHeader("refresh","3");
//在内存中创建一个图片
BufferedImage bufferedImage = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
//得到图片
Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();//2D的笔
//设置图片的背景颜色
graphics.setColor(Color.white);
graphics.fillRect(0,0,80,20);
//给图片写数据
graphics.setColor(Color.BLUE);
graphics.setFont(new Font(null,Font.BOLD,20));
graphics.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
boolean write = ImageIO.write(bufferedImage, "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);
}
}
6.6.4 实现重定向
- 一个web资源(B)收到客户端(A)请求后,他(B)会通知客户端(A)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 location) throws IOException;
- RedirectServlet(测试)
package com.zach.servlet;
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 RedirectServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/*
resp.setHeader("Location","/response_war/img");
resp.setStatus(302);
*/
resp.sendRedirect("/response_war/img");//重定向
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(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地址栏不会变
- 重定向的时候,url地址栏会变
- 相同点:
- 模拟登陆:
- index.jsp
<html>
<body>
<h2>Hello World!</h2>
<%--这里提交的路径,需要寻找到项目的路径--%>
<%--${pageContext.request.contextPath}代表当前的项目--%>
<%--jsp代码里面加上这些话<%@ page contentType="text/html; charset=UTF-8"%>--%>
<%@ page contentType="text/html; charset=UTF-8"%>
<form action="${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>
</body>
</html>
- success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1>Success!!!</h1>
</body>
</html>
- RequestTest
package com.zach.servlet;
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 RequestTest extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//处理请求
String username = req.getParameter("username");//从请求里面 获取参数
String password = req.getParameter("password");//从请求里面 获取参数
System.out.println("username: "+username+"\npassword: "+password);
// 重定向时注意:路径问题,可能导致404
resp.sendRedirect("/response_war/success.jsp");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
6.7 HttpServletRequest
-
请求
-
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中,通过HttpServletRequest这个方法,可以获取客户端的所有信息。
-
获取(前端传递的)参数,请求转发:
-
LoginServlet
package com.zach.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.util.Arrays;
public class LoginServlet extends HttpServlet {
@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[] hobbies = req.getParameterValues("hobbies");
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(hobbies));
System.out.println("=========================");
//通过请求转发
req.getRequestDispatcher("/success.jsp").forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- index.jsp
<body>
<h1>登录</h1>
<div>
<%--这里的表单表示的意思:以post方式提交表单,提交到我们的login请求--%>
<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="hobbies" value="女孩">女孩
<input type="checkbox" name="hobbies" value="代码">代码
<input type="checkbox" name="hobbies" value="唱歌">唱歌
<input type="checkbox" name="hobbies" value="跳舞">跳舞
<input type="checkbox" name="hobbies" value="Rap">Rap
<input type="checkbox" name="hobbies" value="篮球">篮球
<br>
<input type="submit">
</form>
</div>
</body>
- 面试题(同上):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地址栏不会变:307
- 重定向的时候,url地址栏会变:302
- 相同点: