java - Color HttpMessageConverter 但缺少 Color 的默认构造函数

Question

要将 url 参数解码为颜色，我使用此 HttpMessageConverter:

public class ColorHttpMessageConverter implements HttpMessageConverter<Color> {

    @Override
    public boolean canRead(Class<?> clazz, MediaType mediaType) {
        return clazz == Color.class;
    }

    @Override
    public boolean canWrite(Class<?> clazz, MediaType mediaType) {
        return clazz == Color.class;
    }

    @Override
    public List<MediaType> getSupportedMediaTypes() {
        return Collections.singletonList(MediaType.ALL);
    }

    @Override
    public Color read(Class<? extends Color> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {
        byte[] buff = new byte[6];
        if (inputMessage.getBody().read(buff) != buff.length) {
            throw new HttpMessageNotReadableException("Must read 6 bytes.");
        }
        String c = new String(buff);
        return Color.decode("#" + c);
    }

    @Override
    public void write(Color t, MediaType contentType, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException {
        outputMessage.getBody().write(Integer.toHexString(t.getRGB()).substring(2).getBytes());
    }

}

然后我编写一个具有以下映射的休息 Controller :

@Transactional
@RequestMapping("a.jpg")
public ResponseEntity<BufferedImage> getA(Color textcolor) throws IOException {

我调用 URL http://localhost:8080/myapp/rest/a.jpg?textcolor=ffffff 但我在控制台中只得到这个:

No primary or default constructor found for class java.awt.Color

有什么想法吗？

Answer 1

HttpMessageConverter它有一个完全不同的目的，是将 body 转化为其他东西(反之亦然)。你想要的是 Converter<String, Color>反之亦然，因为您想要将请求参数而不是正文转换为 Color 。

public class StringToColorConverter implements Converter<String, Color> {

  public Color convert(String color) {
    return Color.decode("#" + color);
  }

}

反之亦然

public class ColorToStringConverter implements Converter<Color,String> {

  public String convert(Color color) {
    return Integer.toHexString(color.getRGB()).substring(2);
  }

}

现在您可以使用 WebMvcConfigurer 注册它们

@Configuration
public class MyWebConfigurer implements WebMvcConfigurer {

  public void addFormatters(FormatterRegistry registry) {
    registry.addConverter(new StringToColorConverter()):
    registry.addConverter(new ColorToStringConverter()):
  }

}

现在，当该方法参数的类型为 Color 时，应该使用转换器。检测到。