Java 将数据 URL 转换为 BufferedImage
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Convert Data-URL to BufferedImage
提问by Daniel
I have a Data-URL from an image file and have to pass it through to another function. Along this path from Data-URL to the BufferedImage it needs to be a byteArray.
我有一个来自图像文件的数据 URL，必须将它传递给另一个函数。沿着从 Data-URL 到 BufferedImage 的这条路径，它需要是一个 byteArray。
my approach was the following:
我的方法如下：
String dataUrl;
byte[] imageData = dataUrl.getBytes();
// pass the byteArray along the path
// create BufferedImage from byteArray
BufferedImage inputImage = ImageIO.read(new ByteArrayInputStream(imageData));
// If the picture is null, then throw an unsupported image exception.
if (inputImage == null) {
throw new UnknownImageFormatException();
}
The problem is, it always throws the UnknownImageFormatException Exception, which means inputImage is null, which means, the ImageIO.read did not recognize the imagetype.
问题是，它总是抛出 UnknownImageFormatException 异常，这意味着 inputImage 为 null，这意味着 ImageIO.read 无法识别图像类型。
I've used ImageIO.getReaderFormatNames() to get the supported Filenames and got the following list:
我使用 ImageIO.getReaderFormatNames() 来获取支持的文件名并得到以下列表：
Supported Formats:
jpg, BMP, bmp, JPG, jpeg, wbmp, png, JPEG, PNG, WBMP, GIF, gif
The dataURLs I try to pass are like: data:image/png;base64,...or data:image/jpg;base64,...
我尝试传递的 dataURLs 是这样的：data:image/png;base64,...或data:image/jpg;base64,...
As far as I understand, those are in the supported filelist and therefor should be recognized.
据我了解，这些都在支持的文件列表中，因此应该被识别。
What else could cause the inputImage to be null in this case? And more interesting, how do I solve it?
在这种情况下，还有什么可能导致 inputImage 为空？更有趣的是，我该如何解决？
采纳答案by ChristophT
As the comments already said the image data is Base64 encoded. To retrieve the binary data you have to strip the type/encoding headers, then decode the Base64 content to binary data.
正如评论已经说过的，图像数据是 Base64 编码的。要检索二进制数据，您必须去除类型/编码标头，然后将 Base64 内容解码为二进制数据。
String encodingPrefix = "base64,";
int contentStartIndex = dataUrl.indexOf(encodingPrefix) + encodingPrefix.length();
byte[] imageData = Base64.decodeBase64(dataUrl.substring(contentStartIndex));
I use org.apache.commons.codec.binary.Base64from apaches common-codec, other Base64 decoders should work as well.
我使用org.apache.commons.codec.binary.Base64apaches common-codec，其他 Base64 解码器也应该可以工作。
回答by Roman Nikitchenko
The only one problem with RFC2397 string is its specification with everything before data but data:and ,optional:
唯一的一个问题RFC2397字符串是它的一切规范的数据，但之前data:和,可选：
data:[<mediatype>][;base64],<data>
So pure Java 8 solution accounting this would be:
所以纯 Java 8 解决方案会计这将是：
final int dataStartIndex = dataUrl.indexOf(",") + 1;
final String data = dataUrl.substring(dataStartIndex);
byte[] decoded = java.util.Base64.getDecoder().decode(data);
Of course dataStartIndex should be checked.
当然应该检查 dataStartIndex 。
回答by nyuwec
I think, a simple regex replace would be better and more conform to the RFC2397:
我认为，一个简单的正则表达式替换会更好，更符合RFC2397：
java.util.Base64.getDecoder().decode(b64DataString.replaceFirst("data:.+,", ""))
java.util.Base64.getDecoder().decode(b64DataString.replaceFirst("data:.+,", ""))
The RFC states that the data:and the ,are the required prefixes for a data url, therefore it is wise to match for them.
RFC 声明 thedata:和 the,是数据 url 所需的前缀，因此匹配它们是明智的。
