JavaFX : Retrieving Image from server, 找不到合适的构造函数

Question

我正在开发一个 JavaFX 应用程序，我想在其中从本地主机中运行的服务器检索图像。该图像是javafx.scene.Image。但是，当我尝试检索不包含任何类的图像时，我得到没有找到合适的消息转换器，并且当我将图像放入另一个对象中时，我得到一个不同的错误。那么，如何从服务器检索图像？请告诉我。

错误日志:

org.springframework.http.converter.HttpMessageNotReadableException: Could not read document: No suitable constructor found for type [simple type, class javafx.scene.image.Image]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@1eebd84c; line: 1, column: 17] (through reference chain: Model.RestImage["canvasImage"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class javafx.scene.image.Image]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@1eebd84c; line: 1, column: 17] (through reference chain: Model.RestImage["canvasImage"])
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:225)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:209)
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:95)
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:835)
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:819)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:599)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:557)
    at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:475)
    at Controller.AccountController$4.call(AccountController.java:140)
    at Controller.AccountController$4.call(AccountController.java:127)
    at javafx.concurrent.Task$TaskCallable.call(Task.java:1423)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class javafx.scene.image.Image]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@1eebd84c; line: 1, column: 17] (through reference chain: Model.RestImage["canvasImage"])

JavaFX 端代码:

从服务器检索图像:

  private Task<List<RestImage>> fetchCanvasImagesFromServer = new Task<List<RestImage>>() {

        @Override
        protected List<RestImage> call() throws Exception {
            List<RestImage> imageList = new ArrayList<>();
            try {
                for(RestCanvas restCanvas : restCanvases) {
                    RestTemplate rest = StaticRestTemplate.getRest();
                    HttpHeaders requestHeaders = new HttpHeaders();
                    requestHeaders.add("Cookie", "JSESSIONID=" + StaticRestTemplate.jsessionid);
                    HttpEntity<RestImage> requestEntity = new HttpEntity<>(requestHeaders);
                    rest.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
                    rest.getMessageConverters().add(new ByteArrayHttpMessageConverter());
                    ResponseEntity<RestImage> responseEntity = rest.exchange(getCanvasImage+restCanvas.getMcanvasid(), HttpMethod.GET, requestEntity, RestImage.class);
                    imageList.add(responseEntity.getBody());
                }
                return imageList;
            } catch (Exception e) {
                e.printStackTrace();
            }
            return imageList;
        }
    };

RestImage模型:

import javafx.scene.image.Image;

public class RestImage {

    private Image canvasImage;

    private int someId;
// getters and setters
}

服务器端 Controller 代码:

@RequestMapping(value = "/canvasimage/{canvasid}")
    public @ResponseBody
    RestImage getBoardImageAsImage(@PathVariable("canvasid") int canvasid) {
        System.out.println("Board image was called.");
        Person person = this.personService.getCurrentlyAuthenticatedUser();
        RestImage restImage = new RestImage();
        restImage.setSomeId(canvasid);
BufferedImage bufferedImage = ImageIO.read(file);

                    restImage.setCanvasImage(SwingFXUtils.toFXImage(bufferedImage,null));

 return restImage;
}

Answer 1

这种方法的根本问题是框架似乎不知道如何通过网络传递图像。简而言之，您需要找到一些可以在中间容器中轻松传输的格式。通常，对于图像传输，可以从图像中提取原始字节并发送 byte[] ，便于运输。另一端收到后，byte[]可以读回图像。一种转换方式 JavaFX Image进入byte[]首先将其转换为BufferedImage使用SwingFXUtils ，随后使用ImageIO.write()写入 ByteArrayOutputStream并获得byte[]通过toByteArray() 。最后，您可以使用ImageIO.read()和ByteArrayInputStream转换byte[]进入BufferredImage然后JavaFX Image 。另外，根据您在客户端的处理方式，您可以将数据读入 JavaFX Image直接使用 this constructor .

或者，考虑到您无论如何都是从文件中读取图像，您可以将图像读入 byte[]直接与 Files.readAllBytes() 。当您跳过多个解析步骤时，这种方法会明显更快。