SpringBoot HttpMessageConverter消息转换器的使用详解-Java开发

在整个数据流转过程中，前端的请求报文转化为Java对象，Java对象转化为响应报文，这里就用到了消息转换器HttpMessageConverter

消息转化器的作用

将请求报文转化为Java对象
将Java对象转化为响应报文

消息转化器的主要方法

getSupportedMediaTypes：获取支持的MediaType集合（如：text/html，text/plain，application/json）
canRead：判断是否能读（请求）
read：将请求数据进行格式转换（canRead方法返回值为true时调用）
canWrite：判断是否能写（响应）
write：将响应数据进行格式转换（canWrite方法返回值为true时调用）

默认配置的消息转化器

SpringMVC启动时会自动配置一些HttpMessageConverter（WebMvcConfigurationSupport类的addDefaultHttpMessageConverters）方法

源码如下：

	protected final void addDefaultHttpMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
		messageConverters.add(new ByteArrayHttpMessageConverter());
		messageConverters.add(new StringHttpMessageConverter());
		messageConverters.add(new ResourceHttpMessageConverter());
		messageConverters.add(new ResourceRegionHttpMessageConverter());
		try {
			messageConverters.add(new SourceHttpMessageConverter<>());
		}
		catch (Throwable ex) {
			// Ignore when no TransformerFactory implementation is available...
		}
		messageConverters.add(new AllEncompassingFormHttpMessageConverter());
		if (romePresent) {
			messageConverters.add(new AtomFeedHttpMessageConverter());
			messageConverters.add(new RssChannelHttpMessageConverter());
		}
		if (jackson2XmlPresent) {
			Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.xml();
			if (this.applicationContext != null) {
				builder.applicationContext(this.applicationContext);
			}
			messageConverters.add(new MappingJackson2XmlHttpMessageConverter(builder.build()));
		}
		else if (jaxb2Present) {
			messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
		}
		if (jackson2Present) {
			Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();
			if (this.applicationContext != null) {
				builder.applicationContext(this.applicationContext);
			}
			messageConverters.add(new MappingJackson2HttpMessageConverter(builder.build()));
		}
		else if (gsonPresent) {
			messageConverters.add(new GsonHttpMessageConverter());
		}
		else if (jsonbPresent) {
			messageConverters.add(new JsonbHttpMessageConverter());
		}
		if (jackson2SmilePresent) {
			Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.smile();
			if (this.applicationContext != null) {
				builder.applicationContext(this.applicationContext);
			}
			messageConverters.add(new MappingJackson2SmileHttpMessageConverter(builder.build()));
		}
		if (jackson2CborPresent) {
			Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.cbor();
			if (this.applicationContext != null) {
				builder.applicationContext(this.applicationContext);
			}
			messageConverters.add(new MappingJackson2CborHttpMessageConverter(builder.build()));
		}
	}

部分消息转换器解析

名称	描述
MappingJackson2HttpMessageConverter	负责读、写JSON格式数据（利用Jackson）
AllEncompassingFormHttpMessageConverter	负责读、写Form表单数据
Jaxb2RootElementHttpMessageConverter	负责读、写XML格式数据（使用JAXB）
ByteArrayHttpMessageConverter	负责读、写二进制格式数据
StringHttpMessageConverter	负责读、写字符串格式数据
ResourceHttpMessageConverter	负责读、写资源文件数据
SourceHttpMessageConverter	负责读、写资源数据