java web 之springboot教程之二十八----文件上传

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#springboot #file upload #java web

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本文详细介绍了使用SpringBoot实现文件上传的过程，包括pom.xml依赖配置、解决大文件上传问题、异常处理、HTML表单设计及控制器编写。通过具体代码示例，展示了如何配置文件上传限制、处理上传文件及返回上传状态。

1，导入pom.xml包：

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

   <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <optional>true</optional>
   </dependency>
   <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
   </dependency>
</dependencies>

2，启动类设置

package com.example.fileupload;

import org.apache.coyote.http11.AbstractHttp11Protocol;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.embedded.tomcat.TomcatConnectorCustomizer;
import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class FileuploadApplication {

   public static void main(String[] args) {
      SpringApplication.run(FileuploadApplication.class, args);
   }

   @Bean
   public TomcatServletWebServerFactory tomcatEmbedded() {
      TomcatServletWebServerFactory tomcat = new TomcatServletWebServerFactory();
      tomcat.addConnectorCustomizers((TomcatConnectorCustomizer) connector -> {
         if ((connector.getProtocolHandler() instanceof AbstractHttp11Protocol<?>)) {
            //-1 means unlimited
            ((AbstractHttp11Protocol<?>) connector.getProtocolHandler()).setMaxSwallowSize(-1);
         }
      });
      return tomcat;
   }

}

tomcatEmbedded 这段代码是为了解决，上传文件大于10M出现连接重置的问题。此异常内容 GlobalException 也捕获不到。

全局异常捕获，设置一个@ControllerAdvice用来监控Multipart上传的文件大小是否受限，当出现此异常时在前端页面给出提示。利用@ControllerAdvice可以做很多东西，比如全局的统一异常处理等.

package com.example.fileupload.controller;

import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

@ControllerAdvice
public class GlobalExceptionHandler {

    //https://jira.spring.io/browse/SPR-14651
    //4.3.5 supports RedirectAttributes redirectAttributes
    @ExceptionHandler(MultipartException.class)
    public String handleError1(MultipartException e, RedirectAttributes redirectAttributes) {
        redirectAttributes.addFlashAttribute("message", e.getCause().getMessage());
        return "redirect:/uploadStatus";
    }
}

3，html文件编写

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<body>

<h1>Spring Boot file upload example</h1>

<form method="POST" action="/upload" enctype="multipart/form-data">
    <input type="file" name="file" /><br/><br/>
    <input type="submit" value="Submit" />
</form>

</body>
</html>

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<body>

<h1>Spring Boot - Upload Status</h1>

<div th:if="${message}">
    <h2 th:text="${message}"/>
</div>

</body>
</html>

4，controller类编写：

package com.example.fileupload.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

@Controller
public class UploadController {
    //Save the uploaded file to this folder
    private static String UPLOADED_FOLDER = "D://temp//";

    @GetMapping("/")
    public String index() {
        return "upload";
    }

    @PostMapping("/upload")
    public String singleFileUpload(@RequestParam("file") MultipartFile file,
                                   RedirectAttributes redirectAttributes) {
        if (file.isEmpty()) {
            redirectAttributes.addFlashAttribute("message", "Please select a file to upload");
            return "redirect:uploadStatus";
        }

        try {
            // Get the file and save it somewhere
            byte[] bytes = file.getBytes();
            Path path = Paths.get(UPLOADED_FOLDER + file.getOriginalFilename());
            Files.write(path, bytes);

            redirectAttributes.addFlashAttribute("message",
                    "You successfully uploaded '" + file.getOriginalFilename() + "'");

        } catch (IOException e) {
            e.printStackTrace();
        }

        return "redirect:/uploadStatus";
    }

    @GetMapping("/uploadStatus")
    public String uploadStatus() {
        return "uploadStatus";
    }

}

配置文件

#http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#common-application-properties
#search multipart
spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=10MB

通过MultipartFile读取文件信息，如果文件为空跳转到结果页并给出提示；如果不为空读取文件流并写入到指定目录，最后将结果展示到页面。

MultipartFile是Spring上传文件的封装类，包含了文件的二进制流和文件属性等信息，在配置文件中也可对相关属性进行配置，基本的配置信息如下：