Spring Boot应用上传文件时报错的原因及解决方案

private void parseParts(boolean explicit) {
  //...
  MultipartConfigElement mce = this.getWrapper().getMultipartConfigElement();
  //...
  // 读取MultipartConfigElement对象的location属性
  String locationStr = mce.getLocation();
  File location;
  if (locationStr != null && locationStr.length() != 0) {
    location = new File(locationStr);
    if (!location.isAbsolute()) {
      location = (new File((File)context.getServletContext().getAttribute("javax.servlet.context.tempdir"), locationStr)).getAbsoluteFile();
    }
  } else {
    // 如果location属性值为空，则读取Servlet上下文对象的属性“javax.servlet.context.tempdir”值（如：/tmp/tomcat.6574404581312272268.18333/work/Tomcat/localhost/ROOT）
    location = (File)context.getServletContext().getAttribute("javax.servlet.context.tempdir");
  }
  //...
}

spring.servlet.multipart.location=/data/tmp

# MULTIPART (MultipartProperties)
spring.servlet.multipart.enabled=true # Whether to enable support of multipart uploads.
spring.servlet.multipart.file-size-threshold=0B # Threshold after which files are written to disk.
spring.servlet.multipart.location= # Intermediate location of uploaded files.
spring.servlet.multipart.max-file-size=1MB # Max file size.
spring.servlet.multipart.max-request-size=10MB # Max request size.
spring.servlet.multipart.resolve-lazily=false # Whether to resolve the multipart request lazily at the time of file or parameter access.

/**
 * 配置上传文件临时目录
 * @return
 */
@Bean
public MultipartConfigElement multipartConfigElement() {
  MultipartConfigFactory factory = new MultipartConfigFactory();
  // tmp.dir参数在启动脚本中设置
  String path = System.getProperty("tmp.dir");
  if(path == null || "".equals(path.trim())) {
    path = System.getProperty("user.dir");
  }
  String location = path + "/tmp";
  File tmpFile = new File(location);
  // 如果临时目录不存在则创建
  if (!tmpFile.exists()) {
    tmpFile.mkdirs();
  }
  // 明确指定上传文件的临时目录
  factory.setLocation(location);
  return factory.createMultipartConfig();
}