Spring Boot之基本Web开发

学习笔记 : Spring Boot之基本Web开发

@ServletComponentScan的使用

在SpringBootApplication上使用@ServletComponentScan注解后,Servlet、Filter、Listener可以直接通过 @WebServlet、@WebFilter、@WebListener 注解自动注册,无需其他代码哟 !

开发Servlet

1. 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>
   
       <!-- lookup parent from repository -->
       <parent>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-parent</artifactId>
           <version>2.1.6.RELEASE</version>
           <relativePath/>
       </parent>
   
       <groupId>io.github.yubuntu0109</groupId>
       <artifactId>web-servlet</artifactId>
       <version>0.0.1-SNAPSHOT</version>
       <name>web-servlet</name>
       <description>Demo project for Spring Boot</description>
   
       <properties>
           <java.version>11</java.version>
       </properties>
   
       <dependencies>
           <dependency>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-starter-web</artifactId>
           </dependency>
       </dependencies>
   
   </project>

2. MyServlet.java : 自定义Servlet

   package pers.huangyuhui.web.servlet;
   
   import javax.servlet.annotation.WebServlet;
   import javax.servlet.http.HttpServlet;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   
   /**
    * @project: web-servlet
    * @description: learn to use the annotation: @ServletComponentScan
    * @author: 黄宇辉
    * @date: 6/26/2019-9:49 AM
    * @version: 1.0
    * @website: https://yubuntu0109.github.io/
    */
   @WebServlet(name = "MyServlet", urlPatterns = "/helloServlet")
   public class MyServlet extends HttpServlet {
   
       @Override
       protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
           System.out.println("this's my servlet ~");
       }
   }

3. WebServletApplication.java : Spring Boot启动类

   package pers.huangyuhui.webservlet;
   
   import org.springframework.boot.SpringApplication;
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   import org.springframework.boot.web.servlet.ServletComponentScan;
   
   @SpringBootApplication
   @ServletComponentScan
   public class WebServletApplication {
   
       public static void main(String[] args) {
           SpringApplication.run(WebServletApplication.class, args);
       }
   
   }

4. 程序运行结果

   this's my servlet ~

开发Filter

1. MyFilter.java : 自定义过滤器

   package pers.huangyuhui.web.filter;
   
   import javax.servlet.*;
   import javax.servlet.annotation.WebFilter;
   import java.io.IOException;
   
   /**
    * @project: web-servlet
    * @description: learn to user annotation: @ServletComponentScan
    * @author: 黄宇辉
    * @date: 6/26/2019-10:30 AM
    * @version: 1.0
    * @website: https://yubuntu0109.github.io/
    */
   
   @WebFilter(filterName = "MyFile", urlPatterns = "/helloServlet")
   public class MyFilter implements Filter {
   
   
       @Override
       public void init(FilterConfig filterConfig) {
       }
   
       @Override
       public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
           System.out.println("this's my filetr !");
           filterChain.doFilter(servletRequest, servletResponse);
       }
   
       @Override
       public void destroy() {
       }
   }

2. 程序运行结果

   this's my filetr !
   this's my servlet ~

开发Listener

1. MyListener.java : 自定义监听器

   package pers.huangyuhui.web.listener;
   
   import javax.servlet.ServletContextEvent;
   import javax.servlet.ServletContextListener;
   import javax.servlet.annotation.WebListener;
   
   /**
    * @project: web-servlet
    * @description: learn to user annotation: @ServletComponentScan
    * @author: 黄宇辉
    * @date: 6/26/2019-10:54 AM
    * @version: 1.0
    * @website: https://yubuntu0109.github.io/
    */
   @WebListener(value = "MyListenre")
   public class MyListener implements ServletContextListener {
   
       @Override
       public void contextInitialized(ServletContextEvent sce) {
           System.out.println("this's contextInitialized ~");
       }
   
       @Override
       public void contextDestroyed(ServletContextEvent sce) {
           System.out.println("this's contextDestroyed ~");
       }
   
   }

2. 程序运行结果

   this's requestInitialized ~
   this's my filetr !
   this's my servlet ~
   this's requestDestroyed ~

使用Bean注解注册Servlet等组件

WebServletApplication.java : Spring Boot启动类

package pers.huangyuhui.web;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import pers.huangyuhui.web.filter.MyFilter;
import pers.huangyuhui.web.listener.MyListener;
import pers.huangyuhui.web.servlet.MyServlet;

@SpringBootApplication
public class WebServletApplication {

    public static void main(String[] args) {

        SpringApplication.run(WebServletApplication.class, args);
    }

    @Bean
    //使用@Bean注解注册Servlet
    public ServletRegistrationBean getServletRegistration() {
        ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new MyServlet());
        servletRegistrationBean.addUrlMappings("/Bean-helloServlet");
        return servletRegistrationBean;
    }
    /*the result:
        this's my servlet ~
     */

    @Bean
    //使用@Bean注解注册Filter
    public FilterRegistrationBean getFilterRegistrationBean() {
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(new MyFilter());
        filterRegistrationBean.addUrlPatterns("/Bean-helloServlet");
        return filterRegistrationBean;
    }
    /*the result:
        this's my filetr !
        this's my servlet ~
     */

    @Bean
    //使用@Bean注解注册Listener
    public ServletListenerRegistrationBean getServletListenerRegistrationBean() {
        return new ServletListenerRegistrationBean(new MyListener());
    }
     /*the result:
        this's contextInitialized ~
     */

}

静态资源访问

默认策略

简介 : Spring Boot默认会过滤所有的静态资源,而静态资源的位置一共有5个,如下所示. 注意: 按照定义的顺序,5个静态资源位置的优先级依次降低! 但是一般情况下,Spring Boot项目不需要webapp目录,所以在第5个”/“可以暂时不考虑哟 ~

1. classpath:/META-INF/resources/
2. classpath:/resources/
3. classpath:/static/
4. classpath:/pulic/
5. /

• 扩 : 如果你使用的是Intellij IDEA开发工具,记得设置目录类型哟 !

自定义策略

如果默认的静态资源过滤策略不能满足开发需求,也可以自定义资源过滤策略,自定义静态资源过滤策略有如下两种方式 :

1. 在配置文件中定义
2. Java编码定义

第一种方式示例 : 可以在application.properties中直接定义过滤规则(第一行)和静态资源位置(第二行),示例代码如下 :

spring.mvc.static-path-pattern=/static/**
spring.resources.static-locations=classpath:/static/

文件的上传

简介 : 多数文件上传都是通过表单形式提交给服务器的,因此,要实现文件上传功能就需要提供一个上传文件的表单,而此表单必须满足以下三个条件.

1. form表单的method的属性设置为post
2. form表单的enctype属性设置为multipart/form-data
3. 提供<input type="file" name="filename"/>的文件上传输入框

在Spring Boot中可以根据需要在application.properties中对上传的文件进行详细的配置,示例代码如下 :

spring.servlet.multipart.enabled=true
spring.servlet.multipart.file-size-threshold=0
spring.servlet.multipart.location=D://upload//photo
spring.servlet.multipart.max-file-size=5MB
spring.servlet.multipart.max-request-size=10MB
spring.servlet.multipart.resolve-lazily=false

1. 第一行: 设置是否开启文件上传支持,默认为true
2. 第二行: 设置文件写入磁盘的阈值,默认为0
3. 第三行: 指定上传文件的临时保存位置
4. 第四行: 设置上传的单个文件的最大大小,默认为1MB
5. 第五行: 设置多文件上传时文件的总大小,默认为10MB
6. 第六行: 设置文件是否延迟解析,默认为false

示例程序

upload.html : 上传文件页面

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <!-- 验证表单信息 -->
    <script type="text/javascript">
        function check() {
            var file = document.getElementById("file").value;
            if (file.length === 0 || file === "") {
                alert("请选择需要上传的文件 !");
                return false;
            }
            return true;
        }
    </script>
</head>
<body>
<form action="../fileUpload" method="post" enctype="multipart/form-data" onsubmit="return check()">
    请选择文件 <input id="file" type="file" name="uploadfile"/><br>
    <input type="submit" value="上传"/>
</form>
</body>
</html>

FileController.java : 操控文件的控制器

package pers.huangyuhui.web.controller;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletRequest;
import java.io.File;
import java.io.IOException;
import java.util.UUID;

/**
 * @project: web-servlet
 * @description: 操控文件的控制器
 * @author: 黄宇辉
 * @date: 6/26/2019-4:34 PM
 * @version: 1.0
 * @website: https://yubuntu0109.github.io/
 */
@RestController
public class FileController {

    /**
     * @description: 上传文件
     * @param: uploadfile
     * @param: request
     * @date: 2019-06-26 5:00 PM
     * @return: java.lang.String
     */
    @RequestMapping("/fileUpload")
    public String handleFormUpload(MultipartFile uploadfile, HttpServletRequest request) {
        if (!uploadfile.isEmpty() && uploadfile.getSize() > 0) {
            //获取上传文件的原始名称
            final String originFileName = uploadfile.getOriginalFilename();
            //指定上传文件的保存目录
            final String dirPath = request.getServletContext().getRealPath("/upload/photo/");
            //若保存文件的目录不存在,则创建该目录
            File file = new File(dirPath);
            if (!file.exists()) {
                file.mkdirs();
            }
            //使用UUID重命名文件名称(uuid__原始文件名称)
            final String newFileName = UUID.randomUUID() + "__" + originFileName;
            try {
                //将上传的文件保存到目标目录下
                uploadfile.transferTo(new File(dirPath + newFileName));
            } catch (IOException e) {
                e.printStackTrace();
            }
            return "success to upload the file !";
        }
        return "fail to upload the file !";
    }

}