JPEGImageWriteParam抛出ClassCastException

Question

我正在尝试使用以下代码压缩java中的图像

ImageWriter writer = (ImageWriter)  ImageIO.getImageWritersByMIMEType("image/jpeg").next();
JPEGImageWriteParam param = (JPEGImageWriteParam) writer.getDefaultWriteParam();
param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
param.setCompressionType("JPEG");
param.setCompressionQuality(0.2f);
param.setProgressiveMode( ImageWriteParam.MODE_DEFAULT );       

writer.setOutput(ImageIO.createImageOutputStream(outputStream));
writer.write(null, new IIOImage(resizedImg, null, null), param);

第二行JPEGImageWriteParam param = (JPEGImageWriteParam) writer.getDefaultWriteParam();抛出ClassCastException 如果我将其更改为ImageWriteParam param = writer.getDefaultWriteParam(); 它会为行UnsupportedOperationException抛出param.setProgressiveMode( ImageWriteParam.MODE_DEFAULT ); 提前谢谢......

Answer 1

ImageWriter#getDefaultWriteParam()提供了ImageWriteParam而非JPEGImageWriteParam类型的对象，这就是为什么您会遇到类强制转换异常的原因。你应该做的是创建一个新的JPEGImageWriteParam并使用它。

JPEGImageWriteParam param = new JPEGImageWriteParam(<pass your lacale here>);
param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
param.setCompressionType("JPEG");
param.setCompressionQuality(0.2f);
param.setProgressiveMode( ImageWriteParam.MODE_DEFAULT );    

希望这有帮助。