文件上传出现的几个问题

1.上传文件的时候
SPRING REST: The request was rejected because no multipart boundary was found
org.springframework.web.multipart.MultipartException: Could not parse multipart servlet request;
nested exception is org.apache.commons.fileupload.FileUploadException:
the request was rejected because no multipart boundary was found**"
代码如下:

      @Controller 
    public class MultipleFilesRecieve { @RequestMapping ( value = "/saveMultiple", method = RequestMethod.POST ) 
        public String save( FileUploadForm uploadForm ) { 
            List<MultipartFile> files = uploadForm.getFiles( ); 
            List<String> fileNames = new ArrayList<String>( ); 
            if ( null != files && files.size( ) > 0 ) { 
                for ( MultipartFile multipartFile : files ) { 
                    String fileName = multipartFile.getOriginalFilename( ); 
                    fileNames.add( fileName ); 
                } 
            } 
            return "multifileSuccess"; 
        } 
    }

以上问题,根据Stack Overflow大神所说:
The problem isn't in your code - it's in your request. You're missing boundary in your multipart request. As it said in specification:
问题不在您的代码中 - 而在您的请求中。 您在多部分请求中缺少边界。 正如它在规范中所说：
The Content-Type field for multipart entities requires one parameter, "boundary", which is used to specify the encapsulation boundary. The encapsulation boundary is defined as a line consisting entirely of two hyphen characters ("-", decimal code 45) followed by the boundary parameter value from the Content-Type header field.
解决方法就是,把header中定义的 form-data 请求头删掉(Don't supply Content-Type header in the request. It will work.)

2.在使用Spring的RestTemplate进行文件上传的时候包下面的错误,好难找原因,又是Stack Overflow给了启发,其实这个RestTemplate好像不太好上传,因为我是除了文件还有别的参数

Could not write JSON: No serializer found for class java.io.FileDescriptor and no properties discovered to create BeanSerializer

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解决,使用apache的HttpPost

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3.使用RestTemplate时候出现的错误
org.springframework.web.client.RestClientException: Could not write request: no suitable HttpMessageConverter found for request type [org.springframework.util.LinkedMultiValueMap] and content type [application/x-www-form-urlencoded;charset=UTF-8]

post方法使用了MultiValueMap来封装参数，但是无法找到合适的类型转换，仔细查看我的RestTemplate对象获取方式是如下的：

public static RestTemplate getInstance(String charset) {
  StringHttpMessageConverter m = new   StringHttpMessageConverter(Charset.forName(charset));
  RestTemplate restTemplate = new   RestTemplateBuilder().additionalMessageConverters(m).build();
  return restTemplate;
}

我是直接@Autowired注入的RestTemplate对象
使用了RestTemplateBuilder来创建RestTemplate对象，该方式只会为restTemplate模板初始化一个HttpMessageConverter(注：StringHttpMessageConverter间接实现HttpMessageConverter接口)
直接new的话会多几个Converter

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