e697. determining if an image format can be read or written.txt

来自「这里面包含了一百多个JAVA源文件」· 文本 代码 · 共 63 行

By default, the javax.imageio package can read GIF, PNG, and JPEG images and can write PNG and JPEG images. This example demonstrates how to determine if a particular image format can be either read or written using the javax.imageio package. 
    boolean b;
    
    // Check availability using a format name
    b = canReadFormat("foo");          // false
    b = canReadFormat("gif");          // true
    b = canReadFormat("giF");          // true
    b = canWriteFormat("foo");         // false
    b = canWriteFormat("gif");         // false
    b = canWriteFormat("PNG");         // true
    b = canWriteFormat("jPeG");        // true
    
    // Get extension from a File object
    File f = new File("image.jpg");
    String s = f.getName().substring(f.getName().lastIndexOf('.')+1);
    
    // Check availability using a filename extension
    b = canReadExtension(s);
    b = canWriteExtension(s);
    
    // Check availability using a MIME type
    b = canReadMimeType("image/jpg");     // false
    b = canReadMimeType("image/jpeg");    // true
    b = canWriteMimeType("image/gif");    // false
    b = canWriteMimeType("image/jPeg");   // true
    
    // Returns true if the specified format name can be read
    public static boolean canReadFormat(String formatName) {
        Iterator iter = ImageIO.getImageReadersByFormatName(formatName);
        return iter.hasNext();
    }
    
    // Returns true if the specified format name can be written
    public static boolean canWriteFormat(String formatName) {
        Iterator iter = ImageIO.getImageWritersByFormatName(formatName);
        return iter.hasNext();
    }
    
    // Returns true if the specified file extension can be read
    public static boolean canReadExtension(String fileExt) {
        Iterator iter = ImageIO.getImageReadersBySuffix(fileExt);
        return iter.hasNext();
    }
    
    // Returns true if the specified file extension can be written
    public static boolean canWriteExtension(String fileExt) {
        Iterator iter = ImageIO.getImageWritersBySuffix(fileExt);
        return iter.hasNext();
    }
    
    // Returns true if the specified mime type can be read
    public static boolean canReadMimeType(String mimeType) {
        Iterator iter = ImageIO.getImageReadersByMIMEType(mimeType);
        return iter.hasNext();
    }
    
    // Returns true if the specified mime type can be written
    public static boolean canWriteMimeType(String mimeType) {
        Iterator iter = ImageIO.getImageWritersByMIMEType(mimeType);
        return iter.hasNext();
    }