从 spring-MVC 中的 src/main/resources/.. 读取资源

Question

I have a question that makes my head ache. First, my project structure looks like below.

I made a controller, which returns image(*.png) file to the appropriate request.

The code of controller is written below.

@Controller
public class ImageController {

    @GetMapping(value = "/ImageStore.do", produces = MediaType.IMAGE_PNG_VALUE)
    public @ResponseBody byte[] getStoreImage(HttpServletRequest request) throws IOException {
        String image_name = request.getParameter("image_name");
        Resource resource = null;
        try {
            resource = new ClassPathResource("/images/stores/" + image_name);
            if(resource == null) {
                throw new NullPointerException();
            }
        } catch(NullPointerException e) {
            resource = new ClassPathResource("/images/stores/noimage.png");
        }
        InputStream inputStream = resource.getInputStream();
        return IOUtils.toByteArray(inputStream);
    }
}

Q1. I added try-catch phrase to send noimage.png if the request parameter is wrong, or if the filename of request parameter image_name does not exist. But it doesn't seem to work, and it gives me log saying class path resource [images/stores/noima.png] cannot be opened because it does not exist (If you need to know the full stack trace, I will comment below.)

Q2. I have 2 image files, hello.png and noimage.png in the folder /resources/images/stores/ . I can read noimage.png correctly, but if I make request localhost:8080/ImageStore.do?image_name=hello.png , then it makes an error, making the same log in Q1.

Answer 1

There's no reason to think that the constructor would result in a null value.

The exception you are getting is likely from the getInputStream method, which is documented to throw

FileNotFoundException - if the underlying resource doesn't exist

IOException - if the content stream could not be opened

A slight adjustment might help

@Controller
public class ImageController {

    @GetMapping(value = "/ImageStore.do", produces = MediaType.IMAGE_PNG_VALUE)
    public @ResponseBody byte[] getStoreImage(HttpServletRequest request) throws IOException {
        InputStream is = null;
        try {
            String image_name = request.getParameter("image_name");
            is = new ClassPathResource("/images/stores/" + image_name).getInputStream();
        } catch(FileNotFoundException e) {
            is = new ClassPathResource("/images/stores/noimage.png").getInputStream();
        }

        return IOUtils.toByteArray(is);
    }
}

You should include the stack trace, and exception message, which might assist understanding your second query, but I would check that the file really does exist, with the exact name you're using.