一、文件上传原理

1、文件上传的必要前提

①form表单的enctype取值必须是：multipart/form-data；

默认值为application/x-www-form-urlencoded，enctype是表单请求正文的类型

②method属性的取值必须是Post；

③提供一个文件选择域<input type="file"/>

2、原理分析

默认application/x-www-form-urlencoded上传的数据全部是键值对的形式，使用multipart/form-data会将表单分开为几个部分；

二、传统方式的文件上传

HelloController类：

package com.zibo.controller;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

import javax.servlet.http.HttpServletRequest;
import java.io.File;
import java.util.List;

//控制器
@Controller
public class HelloController {
    //设置路径为"/hello"
    @RequestMapping(value = "/hello")
    public String sayHello(HttpServletRequest request) throws Exception {
        //使用fileupload组件来完成文件上传
        //指定文件上传的位置
        String path = request.getSession().getServletContext().getRealPath("/uploads");
        //判断该路径是否存在，若不存在创建该路径
        File file = new File(path);
        System.out.println(path);
        if(!file.exists()){
            boolean mkdirs = file.mkdirs();
            if (mkdirs){
                //解析request对象，获取文件
                DiskFileItemFactory factory = new DiskFileItemFactory();
                ServletFileUpload upload = new ServletFileUpload(factory);
                //解析request
                List<FileItem> items = upload.parseRequest(request);
                //遍历
                for (FileItem item : items) {
                    //判断当前item对象是否是一个上传文件项
                    if(!item.isFormField()){
                        //是上传文件项
                        //获取到上传文件的名称
                        String itemName = item.getName();
                        //完成文件上传
                        item.write(new File(path,itemName));
                        //删除临时文件
                        item.delete();
                    }
                }
            }
        }
        //控制台打印"Hello Spring MVC!"
        System.out.println("Hello Spring MVC!");
        return "success";
    }
}

index.jsp页面：

<%--
  Created by IntelliJ IDEA.
  User: ZiBo
  Date: 2020/8/9
  Time: 14:52
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <h3>入门程序！</h3>
    <h3>文件上传！</h3>
    <form action="hello" method="post" enctype="multipart/form-data">
        选择文件：<input type="file" name="upload"/><br/>
        提交表单：<input type="submit" value="提交表单"/><br/>
    </form>
</body>
</html>

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>org.example</groupId>
  <artifactId>SpringMVC01</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>SpringMVC01 Maven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <spring.version>5.2.8.RELEASE</spring.version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
      <scope>provided</scope>
    </dependency>
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>jsp-api</artifactId>
      <version>2.2</version>
      <scope>provided</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.11.2</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>2.11.2</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations -->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
      <version>2.11.2</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
    <dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>1.4</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>2.7</version>
    </dependency>
  </dependencies>

  <build>
    <finalName>SpringMVC01</finalName>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.1.0</version>
        </plugin>
        <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.22.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-war-plugin</artifactId>
          <version>3.2.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

运行结果（成功上传）：

【SpringMVC】007-SpringMVC文件上传一、文件上传原理二、传统方式的文件上传三、SpringMVC框架文件上传原理分析四、SpringMVC方式的文件上传五、跨服务器文件上传（略）

三、SpringMVC框架文件上传原理分析

备注：

文件解析器代码如下：

<!--    配置文件解析器，名字必须是multipartResolver-->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="10495760"/>
    </bean>

四、SpringMVC方式的文件上传

HelloController类：

package com.zibo.controller;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletRequest;
import java.io.File;
import java.util.List;

//控制器
@Controller
public class HelloController {
    //设置路径为"/hello"
    @RequestMapping(value = "/hello")
    public String sayHello(HttpServletRequest request, MultipartFile upload) throws Exception {
        //使用fileupload组件来完成文件上传
        //指定文件上传的位置
        String path = request.getSession().getServletContext().getRealPath("/uploads");
        //判断该路径是否存在，若不存在创建该路径
        File file = new File(path);
        System.out.println(path);
        if(!file.exists()){
            boolean mkdirs = file.mkdirs();
            if (mkdirs){
                //获取到上传文件的名称
                String filename = upload.getOriginalFilename();
                //完成文件上传
                assert filename != null;
                upload.transferTo(new File(path,filename));
            }
        }
        //控制台打印"Hello Spring MVC!"
        System.out.println("Hello Spring MVC!");
        return "success";
    }
}

spring-mvc.xml：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
    <!--    开启注解扫描-->
    <context:component-scan base-package="com.zibo.controller"/>
    <!--    视图解析器：解析/WEB-INF/pages/文件夹，后缀为.jsp的页面-->
    <!--    前缀为所在文件夹，后缀为文件类型，使用的时候只需要指定文件名字即可-->
    <bean id="internalResourceViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/pages/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
    <!--    配置文件解析器，名字必须是multipartResolver-->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="10495760"/>
    </bean>
    <!--    指定前端控制器不进行拦截的文件夹，其他如css、images文件夹类似-->
    <mvc:resources mapping="/js/**" location="/js/"/>
    <!--    开启SpringMVC注解的支持和自定义类型转换器-->
    <mvc:annotation-driven/>
</beans>

【SpringMVC】007-SpringMVC文件上传一、文件上传原理二、传统方式的文件上传三、SpringMVC框架文件上传原理分析四、SpringMVC方式的文件上传五、跨服务器文件上传（略）

一、文件上传原理

1、文件上传的必要前提

2、原理分析

二、传统方式的文件上传

HelloController类：

index.jsp页面：

pom.xml：

运行结果（成功上传）：

三、SpringMVC框架文件上传原理分析

备注：

四、SpringMVC方式的文件上传

HelloController类：

spring-mvc.xml：

运行结果（上传成功）：

五、跨服务器文件上传（略）

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