更新:
请向下滚动到最后一个代码片段，以获取此答案的更新。
这不是一个令人满意的答案，但是它是对问题的回答:
不，这（几乎肯定）是不可能的。
当将InputStream传递给ImageIO时，它将被内部包装成ImageInputStream。然后将此流传递给ImageReader。具体实现取决于图像数据的类型。（通常从输入数据的前几个字节确定）。
现在，这些ImageReader实现的行为不能被改变或控制得合理。（对于其中一些实现，实际读取甚至发生在本地方法中）。
以下是显示不同行为的示例：
_
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.imageio.ImageIO;
public class MultipleImagesFromSingleStream
{
public static void main(String[] args) throws IOException
{
readJpgAndPng();
readPngAndJpg();
}
private static void readJpgAndPng() throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(createDummyImage("Image 0", 50), "jpg", baos);
ImageIO.write(createDummyImage("Image 1", 60), "png", baos);
byte data[] = baos.toByteArray();
InputStream inputStream = createSlowInputStream(data);
BufferedImage image0 = ImageIO.read(inputStream);
System.out.println("Read " + image0);
BufferedImage image1 = ImageIO.read(inputStream);
System.out.println("Read " + image1);
}
private static void readPngAndJpg() throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(createDummyImage("Image 0", 50), "png", baos);
ImageIO.write(createDummyImage("Image 1", 60), "jpg", baos);
byte data[] = baos.toByteArray();
InputStream inputStream = createSlowInputStream(data);
BufferedImage image0 = ImageIO.read(inputStream);
System.out.println("Read " + image0);
BufferedImage image1 = ImageIO.read(inputStream);
System.out.println("Read " + image1);
}
private static InputStream createSlowInputStream(byte data[])
{
ByteArrayInputStream bais = new ByteArrayInputStream(data);
return new InputStream()
{
private long counter = 0;
@Override
public int read() throws IOException
{
counter++;
if (counter % 100 == 0)
{
System.out.println(
"Read " + counter + " of " + data.length + " bytes");
try
{
Thread.sleep(50);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
return bais.read();
}
};
}
private static BufferedImage createDummyImage(String text, int h)
{
int w = 100;
BufferedImage image =
new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = image.createGraphics();
g.setColor(Color.BLACK);
g.fillRect(0, 0, w, h);
g.setColor(Color.WHITE);
g.drawString(text, 20, 20);
g.dispose();
return image;
}
}
输出结果如下：
Read 100 of 1519 bytes
Read 200 of 1519 bytes
Read 300 of 1519 bytes
Read 400 of 1519 bytes
Read 500 of 1519 bytes
Read 600 of 1519 bytes
Read 700 of 1519 bytes
Read 800 of 1519 bytes
Read 900 of 1519 bytes
Read 1000 of 1519 bytes
Read 1100 of 1519 bytes
Read 1200 of 1519 bytes
Read 1300 of 1519 bytes
Read 1400 of 1519 bytes
Read 1500 of 1519 bytes
Read BufferedImage@3eb07fd3: type = 0 DirectColorModel: rmask=ff000000 gmask=ff0000 bmask=ff00 amask=ff IntegerInterleavedRaster: width = 100 height = 50 #Bands = 4 xOff = 0 yOff = 0 dataOffset[0] 0
Read null
Read 100 of 1499 bytes
Read 200 of 1499 bytes
Read BufferedImage@42110406: type = 6 ColorModel: #pixelBits = 32 numComponents = 4 color space = java.awt.color.ICC_ColorSpace@531d72ca transparency = 3 has alpha = true isAlphaPre = false ByteInterleavedRaster: width = 100 height = 50 #numDataElements 4 dataOff[0] = 3
Read null
请注意，尽管在第二种情况下它没有读取完整的流，但这仍然不一定意味着输入流位于“JPG数据的开头”。它只是意味着它没有读取完整的流！
我也试图深入研究。如果可以确定图像始终只是PNG图像，则可以尝试手动创建一个PNGImageReader实例并连接到其读取过程，以检查何时实际完成第一个图像。但同样，输入流在内部包装成几个其他（缓冲和解压）输入流，并且没有办法合理地检测某个字节集是否已经被用于图像。
因此，我认为在此唯一明智的解决方案是在读取图像后关闭流，并为下一个图像打开新流。
在评论中讨论的一种解决方法是向流添加长度信息。这意味着图像数据的生产者首先将一个int写入流中，描述图像数据的长度。然后，它使用实际的图像数据写入byte[length]数据。
接收者可以使用此信息加载单个图像。
这里作为示例实现了此功能：
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
public class MultipleImagesFromSingleStreamWorkaround
{
public static void main(String[] args) throws IOException
{
workaround();
}
private static void workaround() throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
write(createDummyImage("Image 0", 50), "jpg", baos);
write(createDummyImage("Image 1", 60), "png", baos);
write(createDummyImage("Image 2", 70), "gif", baos);
byte data[] = baos.toByteArray();
InputStream inputStream = createSlowInputStream(data);
BufferedImage image0 = read(inputStream);
System.out.println("Read " + image0);
BufferedImage image1 = read(inputStream);
System.out.println("Read " + image1);
BufferedImage image2 = read(inputStream);
System.out.println("Read " + image2);
showImages(image0, image1, image2);
}
private static void write(BufferedImage bufferedImage,
String formatName, OutputStream outputStream) throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(bufferedImage, formatName, baos);
byte data[] = baos.toByteArray();
DataOutputStream dos = new DataOutputStream(outputStream);
dos.writeInt(data.length);
dos.write(data);
dos.flush();
}
private static BufferedImage read(
InputStream inputStream) throws IOException
{
DataInputStream dis = new DataInputStream(inputStream);
int length = dis.readInt();
byte data[] = new byte[length];
dis.read(data);
ByteArrayInputStream bais = new ByteArrayInputStream(data);
return ImageIO.read(bais);
}
private static InputStream createSlowInputStream(byte data[])
{
ByteArrayInputStream bais = new ByteArrayInputStream(data);
return new InputStream()
{
private long counter = 0;
@Override
public int read() throws IOException
{
counter++;
if (counter % 100 == 0)
{
System.out.println(
"Read " + counter + " of " + data.length + " bytes");
try
{
Thread.sleep(50);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
return bais.read();
}
};
}
private static BufferedImage createDummyImage(String text, int h)
{
int w = 100;
BufferedImage image =
new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = image.createGraphics();
g.setColor(Color.BLACK);
g.fillRect(0, 0, w, h);
g.setColor(Color.WHITE);
g.drawString(text, 20, 20);
g.dispose();
return image;
}
private static void showImages(BufferedImage ... images)
{
SwingUtilities.invokeLater(() ->
{
JFrame f = new JFrame();
f.getContentPane().setLayout(new GridLayout(1,0));
for (BufferedImage image : images)
{
f.getContentPane().add(new JLabel(new ImageIcon(image)));
}
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
});
}
}
更新
这是基于 haraldK 的答案的一个示例实现。它成功地读取了一系列图像，但也有一些限制：
- 似乎必须读取比严格必要的更多字节才能提供第一张图像。
- 它不能加载不同类型的图像（即它不能读取一系列混合的PNG和JPG图像）。
- 具体来说，对我而言，它只适用于JPG图像。对于PNG或GIF，只读取了第一张图片（至少对我而言...）。
然而，我们在此发布它，以便其他人可以轻松测试它：
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.stream.ImageInputStream;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
public class MultipleImagesFromSingleStreamWorking
{
public static void main(String[] args) throws IOException
{
readExample();
}
private static void readExample() throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(createDummyImage("Image 0", 50), "jpg", baos);
ImageIO.write(createDummyImage("Image 2", 70), "jpg", baos);
ImageIO.write(createDummyImage("Image 3", 80), "jpg", baos);
ImageIO.write(createDummyImage("Image 4", 90), "jpg", baos);
ImageIO.write(createDummyImage("Image 5", 100), "jpg", baos);
ImageIO.write(createDummyImage("Image 6", 110), "jpg", baos);
ImageIO.write(createDummyImage("Image 7", 120), "jpg", baos);
byte data[] = baos.toByteArray();
InputStream inputStream = createSlowInputStream(data);
List<BufferedImage> images = readImages(inputStream);
showImages(images);
}
private static List<BufferedImage> readImages(InputStream inputStream)
throws IOException
{
List<BufferedImage> images = new ArrayList<BufferedImage>();
try (ImageInputStream in = ImageIO.createImageInputStream(inputStream))
{
Iterator<ImageReader> readers = ImageIO.getImageReaders(in);
if (!readers.hasNext())
{
throw new AssertionError("No reader for file " + inputStream);
}
ImageReader reader = readers.next();
reader.setInput(in);
try
{
int i = 0;
while (true)
{
BufferedImage image = reader.read(i++);
System.out.println("Read " + image);
images.add(image);
}
}
catch (IndexOutOfBoundsException expected)
{
}
reader.dispose();
}
return images;
}
private static InputStream createSlowInputStream(byte data[])
{
ByteArrayInputStream bais = new ByteArrayInputStream(data);
return new InputStream()
{
private long counter = 0;
@Override
public int read() throws IOException
{
counter++;
if (counter % 100 == 0)
{
System.out.println(
"Read " + counter + " of " + data.length + " bytes");
try
{
Thread.sleep(50);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
return bais.read();
}
};
}
private static BufferedImage createDummyImage(String text, int h)
{
int w = 100;
BufferedImage image =
new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = image.createGraphics();
g.setColor(Color.BLACK);
g.fillRect(0, 0, w, h);
g.setColor(Color.WHITE);
g.drawString(text, 20, 20);
g.dispose();
return image;
}
private static void showImages(List<BufferedImage> images)
{
SwingUtilities.invokeLater(() ->
{
JFrame f = new JFrame();
f.getContentPane().setLayout(new GridLayout(1,0));
for (BufferedImage image : images)
{
f.getContentPane().add(new JLabel(new ImageIcon(image)));
}
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
});
}
}
ImageIO.read不会关闭InputStream，但在结束时它并不一定定位于下一张图片的开头。 - Maurice PerryImageIO本身：通过一些调整，可以看出底层的ImageReader才是导致问题的罪魁祸首。例如，JPEGImageReader确实似乎读取了整个流，而PNGImageReader只 (大约) 读取了必要的数据来确定（第一个）图像。由于无法阻止ImageReader这样做，并且无法检测输入字节是否已经被用于图像，我恐怕这是不可能的。不过这是一个有趣的问题，+1。 - Marco13