JavaWeb三大组件 —— Servlet

刺骨的言语ヽ痛彻心扉 2023-10-14 14:01 10阅读 0赞

**目录**

servlet

注册servlet

父pom

pom文件

1、通过注解注册

2、使用ServletRegistrationBean注册

API三生三世

第一生Servlet

第二生SpringMVC

今生SpringBoot

--------------------

## servlet ##

**Servlet的作用**： 接受请求参数、处理请求，响应结果，**（就是写controller层的get、post等）**  
**Servlet的生命周期：**

*  void init(ServletConfig)：初始化调用一次
 *  void service(ServletRequest request, ServletResponse response)：每次处理请求时候调用
 *  void destroy()：销毁时候

**实现方式:**

*  实现javax.servlet.Servlet接口；
 *  继承javax.servlet.GenericServlet类；
 *  继承javax.servlet.http.HttpServlet类；

常见的都是实现HttpServlet类。重写里边的doGet(),doPost等方法。如图：

![e8d11e1f3b6e434dadcb9559c327ce54.png][]

**注意:**

**本次示例使用的是jdk为1.8版本；**

**javax.servlet** 和 **jakarta.servlet** 是 Java Servlet API 的两个版本。

在过去，Java Servlet API 是由 Sun Microsystems（现在是 Oracle）开发和维护的，其包名以 javax.servlet 开头。然而，从 Java EE 8 开始，Servlet API 的维护权转交给了 Eclipse Foundation 的 Jakarta EE 社区，因此，在最新的 Jakarta EE 版本中，Servlet API 的包名已经更改为 jakarta.servlet。

简而言之，javax.servlet 是旧版本的包名，而 jakarta.servlet 是新版本的包名。这个变化是为了反映 Jakarta EE 作为一个独立的开源项目，并且将标准 Java 技术规范的发展移交给了 Jakarta EE 社区。

需要注意的是，虽然包名发生了变化，但是 Servlet API 的核心功能和用法并没有大的改变。大多数代码可以无缝地迁移到 jakarta.servlet 包下，只需要修改导入语句和相应的依赖。

综上所述，javax.servlet 和 jakarta.servlet 的区别仅在于包名的变化，代表了不同版本的 Java Servlet API

### 注册servlet ###

![37aab9a7854845d5977a71a3e4a46e5f.png][]

#### 父pom ####

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
    
            <version>2.2.5.RELEASE</version>
            <relativePath/> 
        </parent>
        <groupId>com.chensir</groupId>
        <artifactId>springboot</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <name>springboot</name>
        <description>springboot</description>
        <properties>
            <java.version>8</java.version>
        </properties>
    
        <packaging>pom</packaging>
    
        <modules>
            <module>servlet</module>
        </modules>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                </plugin>
            </plugins>
        </build>
    
    </project>

#### pom文件 ####

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <parent>
            <groupId>com.chensir</groupId>
            <artifactId>springboot</artifactId>
            <version>0.0.1-SNAPSHOT</version>
            <relativePath>../pom.xml</relativePath>
        </parent>
    
        <artifactId>servlet</artifactId>
    
        <dependencies>
    
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                </plugin>
            </plugins>
        </build>
    
    </project>

#### 1、通过注解注册 ####

![69d79acb4298459f9c87cbf82613e051.png][]![fe410bae58ad4239aea1dac4216ceb4d.png][]

#### 2、使用ServletRegistrationBean注册 ####

![f756437bca7e472b8a6ad4bffec3f597.png][]

![945252d554e74070bfde45c76c37e64e.png][]

![9a8dcfa1b5634c738f4fc973f7fbe1f4.png][]

![061a10c5f8b042e9bbec76f89a18e216.png][]

### API三生三世 ###

#### 第一生Servlet ####

> 1.新建一个多module的空项目

![4f9fa775872149a0aca68dfc35f24df1.png][]

> 2.新建web项目

![6ff9fc3967504a67850846e79be9b9af.png][]

> 3.选择Java EE8 ，完成

![691eae1c38ef4dea84a5cb41b08ffe44.png][]

> 4.项目目录结构

![dba184c150764e378e4f09dc24941e21.png][]

> 5.修改访问路径

![eae5a20b958f45fcba897e499c16ba70.png][]

![01c75081bb3e49a9983d583093d9fd87.png][]

> 6.查看运行结果

![79f9078aa9d446dca7eda46a89ac540d.png][]

> 7.移除注释，通过xml配置实现

> 8.如何自己写一个servlet

public class TestServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
             // super.doGet(req, resp);
            //查看目前服务器相应编码是什么编码、
           // System.out.println(resp.getCharacterEncoding());
            //设置服务器字符集编码为UTF-8
            //servletResponse.setCharacterEncoding("UTF-8");
            //resp.setHeader("Content-Type","text/html;charset=utf-8");
            //或者只设置下面一个参数就可以，此方法一定要在获取流之前调用才生效
            resp.setContentType("text/html;charset=utf-8");
            //渲染jsp文件
            //RequestDispatcher requestDispatcher = req.getRequestDispatcher("xxx.jsp");
            //requestDispatcher.forward(req,resp);
            
            PrintWriter out = resp.getWriter();
            out.println("<html><body>");
            out.println("<h1>这是TestServlet返回的结果</h1>");
            out.println("</body></html>");
    
        }
    }

> 9.配置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_4_0.xsd"
             version="4.0">
        <servlet>
            <servlet-name>HelloServlet</servlet-name>
            <servlet-class>com.china.servlet.HelloServlet</servlet-class>
        </servlet>
        <servlet>
            <servlet-name>TestServlet</servlet-name>
            <servlet-class>com.china.servlet.TestServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>HelloServlet</servlet-name>
            <url-pattern>/HelloServlet</url-pattern>
        </servlet-mapping>
        <servlet-mapping>
            <servlet-name>TestServlet</servlet-name>
            <url-pattern>/test</url-pattern>
        </servlet-mapping>
    </web-app>

> 10.查看运行结果

![8142c6d43c4041be98e1d51114d3414f.png][]

#### 第二生SpringMVC ####

> 1.新建module，名称叫02\_springmvc

![13883c36be324f2aaa2236016be44dd6.png][]

![fce71ba4e1b74ec69f7274159a0050fc.png][]

> 2.新建文件夹web

![00a48fcf54b24f47ad7c85329244898a.png][]

> 3.点击确定，就会看到如下图，idea自动给我们创建了web.xml

![9c8805aca661410ba0e117a7a93ef5f4.png][]

这时候web文件夹多一个小点点的标识

![a8efd7a8b38c4b4381e3a21a61044d45.png][]

> 4.pom.xml引入相关依赖

<dependencies>
            <dependency>
                <groupId>org.springframework</groupId>
                <artifactId>spring-webmvc</artifactId>
                <version>5.2.0.RELEASE</version>
            </dependency>
            <dependency>
                <groupId>javax.servlet</groupId>
                <artifactId>servlet-api</artifactId>
                <version>2.5</version>
                <scope>provided</scope>
            </dependency>
            <dependency>
                <groupId>javax.servlet.jsp</groupId>
                <artifactId>jsp-api</artifactId>
                <version>2.2.1-b03</version>
                <scope>provided</scope>
            </dependency>
        </dependencies>

> 5.配置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_4_0.xsd"
             version="4.0">
        
        <servlet>
            <servlet-name>springDispatcherServlet</servlet-name>
            <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
            <init-param>
                <param-name>contextConfigLocation</param-name>
                <param-value>classpath:springmvc.xml</param-value>
            </init-param>
            <load-on-startup>1</load-on-startup>
        </servlet>
    
        <servlet-mapping>
            <servlet-name>springDispatcherServlet</servlet-name>
            <url-pattern>/</url-pattern>
            
        </servlet-mapping>
    </web-app>

> 6.新增springmvc.xml

![c433ce2c4e1c432aa6e05c99a1eedd17.png][]

此时springmvc.xml 为原始xml，没有任何bean数据

![b60911403a574b02b0d654a7ee3359b0.png][]

> 7.创建controller文件，TestController

public class TestController implements Controller {
        @Override
        public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
    
            ModelAndView mv = new ModelAndView();
            mv.addObject("name", request.getParameter("name"));
            mv.setViewName("test");
            return mv;
        }
    }

> 8.创建web/WEB\_INF/pages/test.jsp页面

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>
    <html>
        <body>
    
            <h1>页面参数:${name}</h1>
    
        </body>
    </html>

> 9.配置springmvc.xml

> 10.运行，结果如下

![7cde6bdf33e5459eb45718d836a73cea.png][]

> 11.使用注解版

@Controller
    public class Test2Controller {
    
        @RequestMapping("/test2")
        public ModelAndView test(@RequestParam("name") String name){
    
            ModelAndView mv = new ModelAndView();
            mv.addObject("name", name);
            mv.setViewName("test");
            return mv;
    
        }
    }

> 12.springmvx.xml开启controller组件扫描

<context:component-scan base-package="com.china.controller"/>

> 13.运行结果如下

![3c9602c8e42a43bca218843987357d36.png][]

#### 今生SpringBoot ####

> 1.通过IDE创建Spring Boot项目

![97c6a70633a44e9baeaedfbb15d1a3ab.png][]

![95e5113286504b5f9a93119bd1e279b1.png][]

> 2.目录结构

![416447900cca4735973655bd71df7df6.png][]

![3b89bb6703ae4fd7bf101d88727f0f98.png][]

> 3.新建TestController控制器

@Controller
    public class TestController {
    
        @RequestMapping("/test")
        public ModelAndView test(@RequestParam(name = "name", defaultValue = "刘德华") String name){
    
            ModelAndView mv = new ModelAndView();
            mv.addObject("name", name);
            mv.setViewName("test");
            return mv;
        }
    }

> 4.新建/resources/templates/test.ftlh模板文件

> 5.运行项目

![baace3c8d28e490b924922ca04c6664f.png][]

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