Spring RestTemplate - 读取 PNG 标头的 I/O 错误 [英] Spring RestTemplate - I/O error reading PNG header

问题描述

我正在对外部应用程序进行 API 调用(此应用程序将最初加载到其中的所有图像转换为 PNG).如果图像最初是作为 PNG 加载到该应用程序中的，那么 RestTemplate 可以正常工作.如果它最初是作为其他东西加载然后转换为 PNG，那么在 Spring 4.1.1 中尝试使用 RestTemplate 获取它时，下面的代码会引发错误.图像在外部应用程序上显示良好.

I am making an API call to an external app (this app converts all images originally loaded into it to PNG). If the image was originally loaded into that app as a PNG then RestTemplate can get it fine. If it was originally loaded as something else then converted to PNG the below code throws an error when trying to get it using RestTemplate in Spring 4.1.1. The image displays fine on the external app.

Caused by: javax.imageio.IIOException: I/O error reading PNG header！在 com.sun.imageio.plugins.png.PNGImageReader.readHeader(PNGImageReader.java:315) ~[na:1.8.0_20]在 com.sun.imageio.plugins.png.PNGImageReader.readMetadata(PNGImageReader.java:654) ~[na:1.8.0_20]在 com.sun.imageio.plugins.png.PNGImageReader.readImage(PNGImageReader.java:1248) ~[na:1.8.0_20]在 com.sun.imageio.plugins.png.PNGImageReader.read(PNGImageReader.java:1606) ~[na:1.8.0_20]在 org.springframework.http.converter.BufferedImageHttpMessageConverter.read(BufferedImageHttpMessageConverter.java:174) ~[BufferedImageHttpMessageConverter.class:4.1.1.RELEASE]在 org.springframework.http.converter.BufferedImageHttpMessageConverter.read(BufferedImageHttpMessageConverter.java:67) ~[BufferedImageHttpMessageConverter.class:4.1.1.RELEASE]在 org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:104) ~[HttpMessageConverterExtractor.class:4.1.1.RELEASE]在 org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:576) ~[RestTemplate.class:4.1.1.RELEASE]...省略了 74 个常用帧引起:javax.imageio.IIOException:PNG 签名错误！在 com.sun.imageio.plugins.png.PNGImageReader.readHeader(PNGImageReader.java:242) ~[na:1.8.0_20]

Caused by: javax.imageio.IIOException: I/O error reading PNG header! at com.sun.imageio.plugins.png.PNGImageReader.readHeader(PNGImageReader.java:315) ~[na:1.8.0_20] at com.sun.imageio.plugins.png.PNGImageReader.readMetadata(PNGImageReader.java:654) ~[na:1.8.0_20] at com.sun.imageio.plugins.png.PNGImageReader.readImage(PNGImageReader.java:1248) ~[na:1.8.0_20] at com.sun.imageio.plugins.png.PNGImageReader.read(PNGImageReader.java:1606) ~[na:1.8.0_20] at org.springframework.http.converter.BufferedImageHttpMessageConverter.read(BufferedImageHttpMessageConverter.java:174) ~[BufferedImageHttpMessageConverter.class:4.1.1.RELEASE] at org.springframework.http.converter.BufferedImageHttpMessageConverter.read(BufferedImageHttpMessageConverter.java:67) ~[BufferedImageHttpMessageConverter.class:4.1.1.RELEASE] at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:104) ~[HttpMessageConverterExtractor.class:4.1.1.RELEASE] at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:576) ~[RestTemplate.class:4.1.1.RELEASE] ... 74 common frames omitted Caused by: javax.imageio.IIOException: Bad PNG signature! at com.sun.imageio.plugins.png.PNGImageReader.readHeader(PNGImageReader.java:242) ~[na:1.8.0_20]

BufferedImage image = restTemplate.getForObject(getPhotoUrl(), BufferedImage.class, Collections.EMPTY_MAP);

推荐答案

不是使用 getForObject 方法获取 BufferedImage，而是使用 exchange 方法获取字节数组.带有错误 PNG 标头的图像现在会显示在浏览器中.

Instead of using getForObject method to get BufferedImage, using exchange method to get byte array back. Images that have bad PNG headers now display in the browser.

//Set HttpHeaders object
List<MediaType> acceptableMediaTypes = new ArrayList<>();
acceptableMediaTypes.add(MediaType.IMAGE_PNG);
HttpHeaders headers = new HttpHeaders();
headers.setAccept(acceptableMediaTypes);

//Get image from external app with API call
ResponseEntity<byte[]> responseEntity = restTemplate.exchange(getPhotoUrl(), HttpMethod.GET, new HttpEntity<byte[]>(headers), byte[].class);
byte[] image = responseEntity.getBody();

//Display image in browser
if(image != null) {
    InputStream in = new ByteArrayInputStream(image);
    BufferedImage bImageFromConvert = ImageIO.read(in);

    if(bImageFromConvert != null) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(bImageFromConvert, "png", baos);
        byte[] data = baos.toByteArray();
        response.setContentType(MediaType.IMAGE_PNG_VALUE);
        response.getOutputStream().write(data);
    }
}

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