[英]Java get image extension/type using BufferedImage from URL
我熟悉使用圖像 。 我從URL檢索/讀取圖像 ,其中URL沒有文件擴展名。 然后我希望將圖像寫入/保存到本地存儲,但我必須指定圖像文件擴展名(即JPG,PNG等),我無法通過BufferedImage檢索其擴展名。
有人可以指出它是如何做到的? 任何其他方法都可以。
您可以使用ImageIO.getImageReaders(對象輸入)獲取文件的圖像閱讀器。
我自己沒有測試過,但你可以嘗試這個:
ImageInputStream iis = ImageIO.createImageInputStream(file);
Iterator<ImageReader> imageReaders = ImageIO.getImageReaders(iis);
while (imageReaders.hasNext()) {
ImageReader reader = (ImageReader) imageReaders.next();
System.out.printf("formatName: %s%n", reader.getFormatName());
}
如果對象是URL,則使用ImageIO.createImageInputStream(obj)的建議將不起作用。
一種替代方法是使用URLConnection.guessContentTypeFromStream(InputStream流)方法。 此方法通過檢查流的前12個字節來猜測內容類型。
使用此方法的一個復雜因素是它需要標記支持給定的流參數,並且不支持java url.openStream()返回的流。
另外,如果你想確定內容類型並將圖像下載到BufferedImage,那么最好是解決方案只下載一次內容(而不是兩次通過,一次確定內容類型,第二次下載圖片)。
一種解決方案是使用PushbackInputStream。 PushbackInputStream可用於下載第一個初始字節以確定內容類型。 然后可以在流上推回字節,以便ImageIO.read(流)可以完整地讀取流。
可能的方法:
// URLConnection.guessContentTypeFromStream only needs the first 12 bytes, but
// just to be safe from future java api enhancements, we'll use a larger number
int pushbackLimit = 100;
InputStream urlStream = url.openStream();
PushbackInputStream pushUrlStream = new PushbackInputStream(urlStream, pushbackLimit);
byte [] firstBytes = new byte[pushbackLimit];
// download the first initial bytes into a byte array, which we will later pass to
// URLConnection.guessContentTypeFromStream
pushUrlStream.read(firstBytes);
// push the bytes back onto the PushbackInputStream so that the stream can be read
// by ImageIO reader in its entirety
pushUrlStream.unread(firstBytes);
String imageType = null;
// Pass the initial bytes to URLConnection.guessContentTypeFromStream in the form of a
// ByteArrayInputStream, which is mark supported.
ByteArrayInputStream bais = new ByteArrayInputStream(firstBytes);
String mimeType = URLConnection.guessContentTypeFromStream(bais);
if (mimeType.startsWith("image/"))
imageType = mimeType.substring("image/".length());
// else handle failure here
// read in image
BufferedImage inputImage = ImageIO.read(pushUrlStream);
如果從URL獲取圖像,則表示您可以通過InputStream
訪問圖像。 從中您可以使用ImageIO
獲取圖像類型(格式),並使用以下代碼同時創建BufferedImage。
public static BufferedImageWrapper getImageAndTypeFromInputStream(InputStream is) {
String format = null;
BufferedImage bufferedimage = null;
try (ImageInputStream iis = ImageIO.createImageInputStream(is);) {
Iterator<ImageReader> readers = ImageIO.getImageReaders(iis);
if (readers.hasNext()) {
ImageReader reader = readers.next();
format = reader.getFormatName();
reader.setInput(iis);
bufferedimage = reader.read(0);
}
} catch (IOException e) {
logger.error("ERROR DETERMINING IMAGE TYPE!!!", e);
}
return new BufferedImageWrapper(format, bufferedimage);
}
public static class BufferedImageWrapper {
private final String imageType;
private final BufferedImage bufferedimage;
/**
* Constructor
*
* @param imageType
* @param bufferedimage
*/
public BufferedImageWrapper(String imageType, BufferedImage bufferedimage) {
this.imageType = imageType;
this.bufferedimage = bufferedimage;
}
public String getImageType() {
return imageType;
}
public BufferedImage getBufferedimage() {
return bufferedimage;
}
}
它需要初始下載到java tmp目錄,然后在ImageReader嘗試獲取聚合圖像類型后刪除它
public String getImageFileExtFromUrl(URL urlObject) throws URISyntaxException, IOException{
System.out.println("IN DOWNLOAD FILE FROM URL METHOD");
String tmpFolder = System.getProperty("java.io.tmpdir");
String tmpFileStr = tmpFolder + "/" + new Date().getTime();
Files.copy(urlObject.openStream(), Paths.get(tmpFileStr), StandardCopyOption.REPLACE_EXISTING);
File download = new File(tmpFileStr);
System.out.println("FILE DOWNLOAD EXISTS: " + download.exists() );
try{
ImageInputStream iis = ImageIO.createImageInputStream(download);
Iterator<ImageReader> iter = ImageIO.getImageReaders(iis);
ImageReader reader = iter.next();
String formatName = reader.getFormatName();
System.out.println("FOUND IMAGE FORMAT :" + formatName);
iis.close();
return formatName;
}catch(Exception e){
e.printStackTrace();
}finally{
Files.delete(Paths.get(tmpFileStr));
}
return null;
}
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