RestTemplate获取文件的contentType

最新推荐文章于 2024-10-29 16:54:32 发布

weixin_33852020

最新推荐文章于 2024-10-29 16:54:32 发布

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原文链接：https://my.oschina.net/go4it/blog/908961

本文详细介绍了Spring框架中HTTP消息转换器的工作原理及其实现细节，特别是针对AbstractHttpMessageConverter类如何设置默认的HTTP头部信息进行了深入探讨，并展示了ResourceHttpMessageConverter类中资源类型与媒体类型映射的具体实现。

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##org/springframework/http/converter/AbstractHttpMessageConverter.java

protected void addDefaultHeaders(HttpHeaders headers, T t, MediaType contentType) throws IOException{
		if (headers.getContentType() == null) {
			MediaType contentTypeToUse = contentType;
			if (contentType == null || contentType.isWildcardType() || contentType.isWildcardSubtype()) {
				contentTypeToUse = getDefaultContentType(t);
			}
			else if (MediaType.APPLICATION_OCTET_STREAM.equals(contentType)) {
				MediaType mediaType = getDefaultContentType(t);
				contentTypeToUse = (mediaType != null ? mediaType : contentTypeToUse);
			}
			if (contentTypeToUse != null) {
				if (contentTypeToUse.getCharset() == null) {
					Charset defaultCharset = getDefaultCharset();
					if (defaultCharset != null) {
						contentTypeToUse = new MediaType(contentTypeToUse, defaultCharset);
					}
				}
				headers.setContentType(contentTypeToUse);
			}
		}
		if (headers.getContentLength() < 0 && !headers.containsKey(HttpHeaders.TRANSFER_ENCODING)) {
			Long contentLength = getContentLength(t, headers.getContentType());
			if (contentLength != null) {
				headers.setContentLength(contentLength);
			}
		}
	}

##org/springframework/http/converter/ResourceHttpMessageConverter.java

@Override
	protected MediaType getDefaultContentType(Resource resource) {
		if (jafPresent) {
			return ActivationMediaTypeFactory.getMediaType(resource);
		}
		else {
			return MediaType.APPLICATION_OCTET_STREAM;
		}
	}

##org/springframework/http/converter/ActivationMediaTypeFactory.java

class ActivationMediaTypeFactory {

	private static final FileTypeMap fileTypeMap;

	static {
		fileTypeMap = loadFileTypeMapFromContextSupportModule();
	}

	private static FileTypeMap loadFileTypeMapFromContextSupportModule() {
		// See if we can find the extended mime.types from the context-support module...
		Resource mappingLocation = new ClassPathResource("org/springframework/mail/javamail/mime.types");
		if (mappingLocation.exists()) {
			InputStream inputStream = null;
			try {
				inputStream = mappingLocation.getInputStream();
				return new MimetypesFileTypeMap(inputStream);
			}
			catch (IOException ex) {
				// ignore
			}
			finally {
				if (inputStream != null) {
					try {
						inputStream.close();
					}
					catch (IOException ex) {
						// ignore
					}
				}
			}
		}
		return FileTypeMap.getDefaultFileTypeMap();
	}

	public static MediaType getMediaType(Resource resource) {
		String filename = resource.getFilename();
		if (filename != null) {
			String mediaType = fileTypeMap.getContentType(filename);
			if (StringUtils.hasText(mediaType)) {
				return MediaType.parseMediaType(mediaType);
			}
		}
		return null;
	}
}