Java ImageIO.write具有无效的写入程序

Quarkus/JSF/Primefaces项目

我正在尝试将一个调整大小的图像转换回字节数组，我不断得到

validWriter

的

false

，因此，返回的字节数组是空的

private byte[] createBytesFromImage(BufferedImage image, String contentType) {
        ByteArrayOutputStream baosToReturn = new ByteArrayOutputStream();
        try {
            boolean validWriter = ImageIO.write(image, contentType, baosToReturn);
            if (!validWriter) {
                logger.error("Not a Valid Writer");
            }
        } catch (IOException e) {
            baosToReturn = null;
            logger.error("Error trying to convert image " + e);
            e.printStackTrace();
        }
        return baosToReturn.toByteArray();
    }

奥尔格

传递contentType（来自上传的图像）不起作用

您需要为图像提供一段文本，如 “png”

boolean validWriter = ImageIO.write(image, "png", baosToReturn);

与：

    // https://stackoverflow.com/questions/67081086/imageio-write-has-invalid-writer
    private byte[] createBytesFromImage(BufferedImage image, String contentType) {
        ByteArrayOutputStream baosToReturn = new ByteArrayOutputStream();
        String[] splitString = contentType.split("/");
        if (splitString.length == 0) {
            logger.error("++++++++++++++++++++++++++ content type cannot be split");
        } else {
            if (splitString.length != 2) {
                logger.error("++++++++++++++++++++++++++ content type cannot be split to two parts (e.g. image and png)");
            } else {
                logger.info("contentType is split down to " + splitString[0] + " and " + splitString[1]);
                if (!splitString[0].equalsIgnoreCase("image")) {
                    logger.error("++++++++++++++++++++++++++ content type first part is not image");
                } else {                    
                    try {
                        boolean validWriter = ImageIO.write(image, splitString[1], baosToReturn);
                        if (!validWriter) {
                            logger.error("Could not find a Valid Image Writer");
                        }
                    } catch (IOException e) {
                        baosToReturn = null;
                        logger.error("Error trying to convert image " + e);
                        e.printStackTrace();
                    }               
                }
            }
        }
        return baosToReturn.toByteArray();
    }
    

---

仔细看。第二个参数（字符串）允许有哪些值？您传递的是哪种类型的值？实际上有一个方法

ImageIO.getImageWritersByMIMEType（String）

，您可以使用该方法为给定的内容类型获取正确的

ImageWriter

。不幸的是，没有类似的便利方法，如

写入（图像、内容类型、输出）

。。。在大多数情况下，从内容类型中剥离

“image/”

就足够了，这是一个更简单的解决方案。