【小家Spring】Spring MVC容器的web九大组件之---HandlerAdapter源码详解---HttpMessageConverter 消息转换器详解(下)

// Fastjson for Spring MVC Converter. Compatible Spring MVC version 3.2+
// @since 1.2.10
public class FastJsonHttpMessageConverter extends AbstractHttpMessageConverter<Object>
        implements GenericHttpMessageConverter<Object> {
    public FastJsonHttpMessageConverter() {
        super(MediaType.ALL);
    }
  // 永远返回true，表示它想支持所有的类型，所有的MediaType，现在这算一个小Bug
    @Override
    protected boolean supports(Class<?> clazz) {
        return true;
    }
  // 它竟然对泛型Type都没有任何的实现，这也是一个小bug
  // 包括读写的时候  对泛型类型都没有做很好的处理~~~
    public boolean canRead(Type type, Class<?> contextClass, MediaType mediaType) {
        return super.canRead(contextClass, mediaType);
    }
    public boolean canWrite(Type type, Class<?> clazz, MediaType mediaType) {
        return super.canWrite(clazz, mediaType);
    }
  // 这是处理读的方法，主要依赖于JSON.parseObject这个方法解析成一个object
    private Object readType(Type type, HttpInputMessage inputMessage) {
        try {
            InputStream in = inputMessage.getBody();
            return JSON.parseObject(in,
                    fastJsonConfig.getCharset(),
                    type,
                    fastJsonConfig.getParserConfig(),
                    fastJsonConfig.getParseProcess(),
                    JSON.DEFAULT_PARSER_FEATURE,
                    fastJsonConfig.getFeatures());
        } catch (JSONException ex) {
            throw new HttpMessageNotReadableException("JSON parse error: " + ex.getMessage(), ex);
        } catch (IOException ex) {
            throw new HttpMessageNotReadableException("I/O error while reading input message", ex);
        }
    }
}

// 这个类很简单，就是对Resource的一个包装  所以它和`application/octet-stream`也是有关的
// @since 4.3
public class ResourceRegion {
  private final Resource resource;
  private final long position;
  private final long count;
  ...
}

public class PropertiesHttpMessageConverter extends AbstractHttpMessageConverter<User> {
    // 用于仅仅只处理我自己自定义的指定的MediaType
    private static final MediaType DEFAULT_MEDIATYPE = MediaType.valueOf("application/properties");
    public PropertiesHttpMessageConverter() {
        super(DEFAULT_MEDIATYPE);
        setDefaultCharset(StandardCharsets.UTF_8);
    }
    // 要求入参、返回值必须是User类型我才处理
    @Override
    protected boolean supports(Class<?> clazz) {
        return clazz.isAssignableFrom(User.class);
    }
    @Override
    protected User readInternal(Class<? extends User> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
        InputStream is = inputMessage.getBody();
        Properties props = new Properties();
        props.load(is);
        // user的三个属性
        String id = props.getProperty("id");
        String name = props.getProperty("name");
        String age = props.getProperty("age");
        return new User(Integer.valueOf(id), name, Integer.valueOf(age));
    }
    @Override
    protected void writeInternal(User user, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
        OutputStream os = outputMessage.getBody();
        Properties properties = new Properties();
        // 属性判空此处我就不做了~~~
        properties.setProperty("id", user.getId().toString());
        properties.setProperty("name", user.getName());
        properties.setProperty("age", user.getAge().toString());
        properties.store(os, "user comments");
    }
}

@Configuration
@EnableWebMvc
public class WebMvcConfig extends WebMvcConfigurerAdapter {
    @Override
    public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
        // 因为此转换器职责已经足够单一，所以放在首位是木有问题的~
        converters.add(0, new PropertiesHttpMessageConverter());
        // 若放在末尾，将可能不会生效~~~~（比如如果Fastjson转换器 处理所有的类型的话，所以放在首位最为保险）
        //converters.add(0, new PropertiesHttpMessageConverter());
    }
}

    @ResponseBody
    @RequestMapping(value = "/test/properties", method = RequestMethod.POST)
    public User upload(@RequestBody User user) {
        System.out.println(user);
        return user;
    }

@Override
    public boolean canWrite(Class<?> clazz, MediaType mediaType) {
        return (AnnotationUtils.findAnnotation(clazz, XmlRootElement.class) != null && canWrite(mediaType));
    }