HttpMessageConvertersAutoConfiguration自动配置类

在我们日常的web开发过程中肯定都用过@RequestBody、@ResponseBody注解，其作用就是将输入输出参数解析成Json,但是Http请求和响应都是基于报文的，意味着浏览器与服务器之间的交互时通过原始文本进行数据同i性能的，这里其实就是HttpMessageConverter在起作用。

首先来看下HttpMessageConvertersAutoConfiguration配置类的源码

HttpMessageConvertersAutoConfiguration源码

@Configuration(proxyBeanMethods = false) //标明是配置类
@ConditionalOnClass(HttpMessageConverter.class)//在此类存在时生效
@Conditional(NotReactiveWebApplicationCondition.class) //判断非Reactive环境
@AutoConfigureAfter({ GsonAutoConfiguration.class, JacksonAutoConfiguration.class, JsonbAutoConfiguration.class }) //配置类执行顺序
@Import({ JacksonHttpMessageConvertersConfiguration.class, GsonHttpMessageConvertersConfiguration.class,
		JsonbHttpMessageConvertersConfiguration.class }) //引入配置
public class HttpMessageConvertersAutoConfiguration {

	static final String PREFERRED_MAPPER_PROPERTY = "spring.http.converters.preferred-json-mapper";

	@Bean
	@ConditionalOnMissingBean
	public HttpMessageConverters messageConverters(ObjectProvider<HttpMessageConverter<?>> converters) {
		return new HttpMessageConverters(converters.orderedStream().collect(Collectors.toList()));
	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(StringHttpMessageConverter.class)
	@EnableConfigurationProperties(HttpProperties.class)
	protected static class StringHttpMessageConverterConfiguration {

		@Bean
		@ConditionalOnMissingBean
		public StringHttpMessageConverter stringHttpMessageConverter(HttpProperties httpProperties) {
			StringHttpMessageConverter converter = new StringHttpMessageConverter(
					httpProperties.getEncoding().getCharset());
			converter.setWriteAcceptCharset(false);
			return converter;
		}

	}

	static class NotReactiveWebApplicationCondition extends NoneNestedConditions {

		NotReactiveWebApplicationCondition() {
			super(ConfigurationPhase.PARSE_CONFIGURATION);
		}

		@ConditionalOnWebApplication(type = Type.REACTIVE)
		private static class ReactiveWebApplication {

		}

	}

}

从源码中我们可以看到此配置类给Ioc容器中添加了messageConverters和stringHttpMessageConverter这两个bean

HttpMessageConvertersAutoConfiguration

首先先看这一段代码

@Bean
@ConditionalOnMissingBean //容器不存在时添加
//使用@Bean时 参数知己从容器中获取 实现注入
public HttpMessageConverters messageConverters(ObjectProvider<HttpMessageConverter<?>> converters) {
	return new HttpMessageConverters(converters.orderedStream().collect(Collectors.toList()));
}

执行完毕后会查询到这些converter
converters

其中我们可以看到StringHttpMessageConverter,这是为了处理不同编码。

StringHttpMessageConverter源码

我们可以看到如下代码

@Override
protected void writeInternal(String str, HttpOutputMessage outputMessage) throws IOException {
	HttpHeaders headers = outputMessage.getHeaders();
	if (this.writeAcceptCharset && headers.get(HttpHeaders.ACCEPT_CHARSET) == null) {
		headers.setAcceptCharset(getAcceptedCharsets());
	}
	Charset charset = getContentTypeCharset(headers.getContentType());
	StreamUtils.copy(str, charset, outputMessage.getBody());
}

//---------------------------------------------------------
//为了方便 同时把StreamUtils.copy的代码放在这里

public static void copy(String in, Charset charset, OutputStream out) throws IOException {
	Assert.notNull(in, "No input String specified");
	Assert.notNull(charset, "No charset specified");
	Assert.notNull(out, "No OutputStream specified");

    //获取输出流
	Writer writer = new OutputStreamWriter(out, charset);
	//将数据写入
	writer.write(in);
	writer.flush();
}