restful api上传文件（基础）-springboot

基于restful api格式的文件上传（只是上传到本地）：

package com.nxz.controller;

import com.nxz.entity.FileInfo;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

import java.io.File;
import java.io.IOException;
import java.util.Date;

@RestController
@RequestMapping("/file")
public class FileController {
    @PostMapping
    public FileInfo update(MultipartFile file) throws IOException {

        System.out.println(file.getName());
        System.out.println(file.getOriginalFilename());
        System.out.println(file.getSize());

        String holder = "G:\\0001-myproject\\mysecurity\\mysecurity-demo\\src\\main\\java\\com\\nxz\\controller";

        File localFile = new File(holder, new Date().getTime() + ".txt");

        file.transferTo(localFile);

        return new FileInfo(localFile.getAbsolutePath());
    }

}

测试用例：

   //伪造的mvc环境
    @Autowired
    private WebApplicationContext webApplicationContext;
    private MockMvc mockMvc;
    @Before
    public void before() {
        mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
    }
    @Test
    public void whenUploadSuccess() throws Exception {
        String file = mockMvc.perform(MockMvcRequestBuilders.fileUpload("/file")
                .file(new MockMultipartFile("file", "test.txt", "multipart/form-data", "hello".getBytes("UTF-8"))))
                .andExpect(MockMvcResultMatchers.status().isOk())
                .andReturn().getResponse().getContentAsString();
        System.out.println(file);
    }

测试用例执行完之后输出文件绝对路径：

{"path":"G:\\mysecurity\\mysecurity-demo\\src\\main\\java\\com\\nxz\\controller\\1556463660034.txt"}

下载：

 @GetMapping("/{id}")
    public void downLoad(@PathVariable String id,
                         HttpServletRequest request,
                         HttpServletResponse response) throws IOException {
        String holder = "G:\\0001-myproject\\mysecurity\\mysecurity-demo\\src\\main\\java\\com\\nxz\\controller";
        try (
                InputStream inputStream = new FileInputStream(new File(holder, id + ".txt"));
                OutputStream outputStream = response.getOutputStream();
        ) {
            response.setContentType("application/x-download");
            response.addHeader("Content-Disposition", "attachment;filename=test.txt");//重新定义下载后名称
            //将文件输入流复制到输出刘超过年 commons-io依赖
            IOUtils.copy(inputStream, outputStream);
            outputStream.flush();
        }

    }

访问：http://localhost:8080/user/1

springboot中上传文件：

java中和文件上传的类又两个：CommonsMultipartResolver，另一个就是StandardServletMultipartResolver，其中commonsMultipartResolver需要commons-fileupload支持，二StandardServletMultipartReslover是servlet3.0默认支持的，tomcat7以上版本就开始支持servlet7.0，springboot22.0之后支持的tomcat版本在7之后，因此是支持StandardServletMultipartReslover的

首先 springboot只要配置好pom（有spring-boot-starter-web依赖），就能自动支持文件上传（包括单文件和多文件），那么springboot中文件上传是怎样起作用的

1、pom依赖，下边这些依赖中，和配置文件上传有关的就是spring-boot-autoconfig依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

---->>>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.1.3.RELEASE</version>
      <scope>compile</scope>
    </dependency>

---->>>>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-autoconfigure</artifactId>
      <version>2.1.3.RELEASE</version>
      <scope>compile</scope>
    </dependency>

2、那么看下spring-boot-autoconfig jar包中的spring.factories文件中的内容，这个文件中全都是和springboot自动配置相关的类的全文件名，其中和文件上传有关的是

org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\

3、进入这个类中（具体个各种autoconfiguration自动加载类是什么时候加载的，需要看springboot的启动来注解和启动类）

@Configuration
@ConditionalOnClass({ Servlet.class, StandardServletMultipartResolver.class,
        MultipartConfigElement.class }) //这个注解表示存在servlet、StandardServletMultipartResolver、multipartConfigElement文件时才加载该类
@ConditionalOnProperty(prefix = "spring.servlet.multipart", name = "enabled", matchIfMissing = true)//配置文件的前缀
@ConditionalOnWebApplication(type = Type.SERVLET)//servlet
@EnableConfigurationProperties(MultipartProperties.class)//配置文件类
public class MultipartAutoConfiguration {

    private final MultipartProperties multipartProperties;

    public MultipartAutoConfiguration(MultipartProperties multipartProperties) {
        this.multipartProperties = multipartProperties;
    }

    @Bean
    @ConditionalOnMissingBean({ MultipartConfigElement.class,
            CommonsMultipartResolver.class })//当没有commonsMultipartResolver文件时，初始化该bean
    public MultipartConfigElement multipartConfigElement() {
        return this.multipartProperties.createMultipartConfig();
    }

    @Bean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
    @ConditionalOnMissingBean(MultipartResolver.class)
    public StandardServletMultipartResolver multipartResolver() {
        StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();//springboot默认的文件上传的类
        multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
        return multipartResolver;
    }

}