使用“ ImageIO.write（）” API调用我得到NullPointerException

问题描述

通过 ImageIO.write（） API调用，当我传递不存在的路径时，会得到 NullPointerException \\abc\abc.png 。我故意通过不存在的路径来测试某些东西，但没有得到 FileNotFoundException ，而是得到了 NPE 。这是为什么？

With ImageIO.write() API call, I get NullPointerException when I pass a non-existent path like "\\abc\abc.png". I pass the non-existent path purposely to test something but instead of getting FileNotFoundException, I get NPE. Why is that?

ImageIO.write（） API应该抛出 IOException 但不要解释为什么我得到 NPE 。

ImageIO.write() API is supposed to throw IOException but don't why I get NPE.

我使用异常消息字符串在消息中显示它框，但在这种情况下 NPE.getLocalizedMessage（）返回空字符串，因此弹出框为空，上面只有一个图标。

I use exception message string to show it in a message box to user but in this case NPE.getLocalizedMessage() returns empty string and hence the popup is empty with just an icon on it.

推荐答案

他是对。例如，这段代码：

He is right, though. For example, this code:

public static void main(String[] args) throws IOException {
 BufferedImage image = new BufferedImage(32, 32, BufferedImage.TYPE_INT_ARGB);
 File out = new File("\\\\ABC\\abc.png");
 ImageIO.write(image, "png", out);
}

给予

java.io.FileNotFoundException: \\ABC\abc.png (The network path was not found)
at java.io.RandomAccessFile.open(Native Method)
at java.io.RandomAccessFile.<init>(RandomAccessFile.java:233)
at javax.imageio.stream.FileImageOutputStream.<init>(FileImageOutputStream.java:69)
at com.sun.imageio.spi.FileImageOutputStreamSpi.createOutputStreamInstance(FileImageOutputStreamSpi.java:55)
at javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:419)
at javax.imageio.ImageIO.write(ImageIO.java:1530)
at javaapplication145.JavaApplication145.main(JavaApplication145.java:24)
Exception in thread "main" java.lang.NullPointerException
at javax.imageio.ImageIO.write(ImageIO.java:1538)
at javaapplication145.JavaApplication145.main(JavaApplication145.java:24)

原因是 FileImageOutputStreamSpi.createOutputStreamInsta因为吞下FileNotFoundException，然后当 ImageIO.write 试图关闭未打开的流时，NPE出现。

The reason is that FileImageOutputStreamSpi.createOutputStreamInstance swallows the FileNotFoundException and then the NPE comes when ImageIO.write tries to close a stream that didn't open.

为什么这么残酷地抑制异常，我不知道。代码片段是

Why the exception is suppressed so brutally, I don't know. The code fragment is

try {
 return new FileImageOutputStream((File)output);
} catch (Exception e) {
 e.printStackTrace();
 return null;
}

唯一的解决方案是验证路径 before 尝试使用ImageIO。

The only solution is to verify the path before attempting to use ImageIO.

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