SpringCloud升级之路2020.0.x版-29.Spring Cloud OpenFeign 的解析(2)

//由于初始化顺序以及 NamedContextFactory 的 Configuration 初始化的原因，这里需要注入 ObjectFactory 而不是直接注入 HttpMessageConverters 防止找不到 Bean
@Autowired
private ObjectFactory<HttpMessageConverters> messageConverters;

@Bean
@ConditionalOnMissingBean
public Decoder feignDecoder() { 
	return new OptionalDecoder(new ResponseEntityDecoder(new SpringDecoder(this.messageConverters)));
}

@Bean
@ConditionalOnMissingBean
//我们这里忽略 Pageable 类存在的情况
//针对 Spring Data 的分页包装 Pageable 的兼容实现也比较简单，这里忽略
@ConditionalOnMissingClass("org.springframework.data.domain.Pageable")
public Encoder feignEncoder(ObjectProvider<AbstractFormWriter> formWriterProvider) {
	return springEncoder(formWriterProvider, encoderProperties);
}

private Encoder springEncoder(ObjectProvider<AbstractFormWriter> formWriterProvider,
	FeignEncoderProperties encoderProperties) {
    AbstractFormWriter formWriter = formWriterProvider.getIfAvailable();
    
    if (formWriter != null) {
    	return new SpringEncoder(new SpringPojoFormEncoder(formWriter), this.messageConverters, encoderProperties);
    }
    else {
    	return new SpringEncoder(new SpringFormEncoder(), this.messageConverters, encoderProperties);
    }
}

public interface HttpMessageConverter<T> {
    //判断 clazz 类型是否可以被当前 HttpMessageConverter 所读取
	boolean canRead(Class<?> clazz, @Nullable MediaType mediaType);
    //判断 clazz 类型是否可以被当前 HttpMessageConverter 写
	boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType);
    //获取所有支持的 MediaType
	List<MediaType> getSupportedMediaTypes();
    //通过 clazz 类型获取该 HttpMessageConverter 支持的 MediaType
    //默认实现是，如果该类型可以被当前 HttpMessageConverter 读或者写，那么返回 getSupportedMediaTypes 所有支持的 MediaType
	default List<MediaType> getSupportedMediaTypes(Class<?> clazz) {
		return (canRead(clazz, null) || canWrite(clazz, null) ?
				getSupportedMediaTypes() : Collections.emptyList());
	}

    //从 inputMessage 中读取并解析出 clazz 类型的对象，当请求的 Content-Type 为支持的 MediaType 时
	T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
			throws IOException, HttpMessageNotReadableException;

    //将对象 t 序列化写入 HttpOutputMessage，当请求的 accept 为支持的 MediaType 时
	void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage)
			throws IOException, HttpMessageNotWritableException;

}

public class CustomizedHttpMessageConverter implements HttpMessageConverter<Student> {
	@Override
	public boolean canRead(Class<?> clazz, MediaType mediaType) {
		return clazz.equals(Student.class);
	}

	@Override
	public boolean canWrite(Class<?> clazz, MediaType mediaType) {
		return clazz.equals(Student.class);
	}
	
	public static class StudentMediaType extends MediaType {
		public StudentMediaType() {
			super("application", "student", StandardCharsets.UTF_8);
		}
	}

	@Override
	public List<MediaType> getSupportedMediaTypes() {
		return List.of(new StudentMediaType());
	}

	@Override
	public Student read(Class<? extends Student> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
		String temp = StreamUtils.copyToString(inputMessage.getBody(), StandardCharsets.UTF_8);
		String[] split = temp.split(",");
		return new Student(
				Long.parseLong(split[0]),
				split[1]);
	}

	@Override
	public void write(Student student, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
		outputMessage.getBody().write((student.getId() + "," + student.getName()).getBytes(StandardCharsets.UTF_8));
	}
}

@Configuration(proxyBeanMethods = false)
public class TestConfig implements WebMvcConfigurer {
	@Override
	public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
		converters.add(new CustomizedHttpMessageConverter());
	}
}

@RestController
@RequestMapping("/test")
public class TestController {
	@PostMapping("/post-to-student")
	public Student postToStudent(@RequestBody Student student) {
		return student;
	}
}

Content-Type:application/student
Accept:application/student

1,zhx

@Override
public Object decode(final Response response, Type type) throws IOException, FeignException {
    //是否是带有形参的 HttpEntity<?> 
	if (isParameterizeHttpEntity(type)) {
	    //将形参类型取出
		type = ((ParameterizedType) type).getActualTypeArguments()[0];
		//使用形参类型，解析 response
		Object decodedObject = this.decoder.decode(response, type);
        //填充 HttpEntity 其中的返回对象，状态码等信息
		return createResponse(decodedObject, response);
	}
	else if (isHttpEntity(type)) {
	    //空形参，代表没有 body 或者忽略 body，仅填充 HttpEntity 状态码等信息
		return createResponse(null, response);
	}
	else {
	    //如果不是 HttpEntity，直接解码
		return this.decoder.decode(response, type);
	}
}