转自网络
判断文件的类型，而不是判断文件的后缀名
import java.io.*;
import javax.imageio.*;
import java.util.*;
import javax.imageio.stream.*;
public class Test {
public static void main(String[] args) {
File f = new File("c://test//3.jpg");
if (f.exists()) {
System.out.println(getFormatInFile(f));
}
}
// Returns the format of the image in the file 'f'.
// Returns null if the format is not known.
public static String getFormatInFile(File f) {
return getFormatName(f);
}
// Returns the format name of the image in the object 'o'.
// Returns null if the format is not known.
private static String getFormatName(Object o) {
try {
// Create an image input stream on the image
ImageInputStream iis = ImageIO.createImageInputStream(o);
// Find all image readers that recognize the image format
Iterator iter = ImageIO.getImageReaders(iis);
if (!iter.hasNext()) {
// No readers found
return null;
}
// Use the first reader
ImageReader reader = (ImageReader) iter.next();
// Close stream
iis.close();
// Return the format name
return reader.getFormatName();
} catch (IOException e) {
//
}
// The image could not be read
return null;
}
}