SpringBoot默认的json解析方案

HttpMessageConverter

HttpMessageConverter是一个消息转换工具，有两方面的功能：

1.将服务端返回的对象序列化成json字符串
2.将前端传过来的json字符串反序列化成java对象

SpringBoot默认的json解析方案

所有的json生成都离不开相关的HttpMessageConverter。SpringMVC自动配置了Jackson和Gson的HttpMessageConverter，SpringBoot对此做了自动化配置：

1.Jackson的自动化配置类
方式一：org.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(ObjectMapper.class)
	@ConditionalOnBean(ObjectMapper.class)
	@ConditionalOnProperty(name = HttpMessageConvertersAutoConfiguration.PREFERRED_MAPPER_PROPERTY,
			havingValue = "jackson", matchIfMissing = true)
	static class MappingJackson2HttpMessageConverterConfiguration {

		@Bean
		@ConditionalOnMissingBean(value = MappingJackson2HttpMessageConverter.class,
				ignoredType = {
						"org.springframework.hateoas.server.mvc.TypeConstrainedMappingJackson2HttpMessageConverter",
						"org.springframework.data.rest.webmvc.alps.AlpsJsonHttpMessageConverter" })
		MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter(ObjectMapper objectMapper) {
			return new MappingJackson2HttpMessageConverter(objectMapper);
		}

	}

方式二：org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration

@Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(Jackson2ObjectMapperBuilder.class)
	static class JacksonObjectMapperConfiguration {

		@Bean
		@Primary
		@ConditionalOnMissingBean
		ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
			return builder.createXmlMapper(false).build();
		}

	}

2.Gson的自动化配置类
org.springframework.boot.autoconfigure.http.GsonHttpMessageConvertersConfiguration

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnBean(Gson.class)
	@Conditional(PreferGsonOrJacksonAndJsonbUnavailableCondition.class)
	static class GsonHttpMessageConverterConfiguration {

		@Bean
		@ConditionalOnMissingBean
		GsonHttpMessageConverter gsonHttpMessageConverter(Gson gson) {
			GsonHttpMessageConverter converter = new GsonHttpMessageConverter();
			converter.setGson(gson);
			return converter;
		}

	}

自定义日期字段格式化

1.使用@JsonFormat注解

	@JsonFormat(pattern = "yyyy-MM-dd")
    private Date birthday;

劣势：对每个实体类中的日期字段都需要添加此注解

2.提供MappingJackson2HttpMessageConverter类
在配置类中提供MappingJackson2HttpMessageConverter类，使用ObjectMapper 做全局的日期字段格式化（或者配置其他属性）。

@Configuration
public class WebMVCConfig {
    @Bean
    MappingJackson2HttpMessageConverter httpMessageConverter(){
        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        ObjectMapper om = new ObjectMapper();
        om.setDateFormat(new SimpleDateFormat("yyyy-MM-dd"));
        converter.setObjectMapper(om);
        return converter;
    }
}

此类会代替SpringBoot默认的json解析方案。事实上，此类中起作用的是ObjectMapper 类，因此也可直接配置此类。

3.提供ObjectMapper 类
在配置类中提供ObjectMapper 类。

@Configuration
public class WebMVCConfig {

    @Bean
    ObjectMapper om(){
        ObjectMapper om = new ObjectMapper();
        om.setDateFormat(new SimpleDateFormat("yyyy-MM-dd"));
        return om;
    }
}