原理
我们知道springboot的mvc自动配置在WebMvcAutoConfiguration
配置类中
在该类中,有一个WebMvcAutoConfigurationAdapter
类,实现了WebMvcConfigurer
接口,并实现了configureMessageConverters
方法,该方法就可以添加一些MessageConverter
.
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
this.messageConvertersProvider
.ifAvailable((customConverters) -> converters.addAll(customConverters.getConverters()));
}
customConverters.getConverters()实现:getConverters方法就是一个普通的get方法,那么converters的初始化可能就在该类创建的时候赋值的。
找到该类的构造方法:
public HttpMessageConverters(boolean addDefaultConverters, Collection<HttpMessageConverter<?>> converters) {
//调用getDefaultConverters()方法,并赋值给converters
List<HttpMessageConverter<?>> combined = getCombinedConverters(converters,
addDefaultConverters ? getDefaultConverters() : Collections.emptyList());
combined = postProcessConverters(combined);
this.converters = Collections.unmodifiableList(combined);
}
getDefaultConverters
方法,内部会调用父类的getMessageConverters
方法
调用本类的addDefaultHttpMessageConverters
方法
addDefaultHttpMessageConverters
方法:这里会配置一些默认的消息转换器,并且从成员变量判断是否需要添加其他的消息转换器。
protected final void addDefaultHttpMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
messageConverters.add(new ByteArrayHttpMessageConverter());
messageConverters.add(new StringHttpMessageConverter());
messageConverters.add(new ResourceHttpMessageConverter());
messageConverters.add(new ResourceRegionHttpMessageConverter());
if (!shouldIgnoreXml) {
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 (!shouldIgnoreXml) {
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 (kotlinSerializationJsonPresent) {
messageConverters.add(new KotlinSerializationJsonHttpMessageConverter());
}
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()));
}
}
成员变量的初始化:这里判断一些场景是否存在,如果存在,则赋值为true,进而导入相关消息转换器
自定义消息转换器
通过上文分析,我们只需要实现WebMvcConfigurer
接口,并实现了configureMessageConverters
方法,就可以达到自定义消息转换器的目的。
例如,我不想用jackson了,想用fastjson的消息转换器,我们可以添加fastjson相关的MessageConverter
就可以了
@Configuration
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
FastJsonHttpMessageConverter fastConverter = new FastJsonHttpMessageConverter();
List<MediaType> fastMediaTypes = new ArrayList<>();
fastMediaTypes.add(MediaType.TEXT_HTML);
fastMediaTypes.add(MediaType.APPLICATION_JSON);
fastConverter.setSupportedMediaTypes(fastMediaTypes);
FastJsonConfig fastJsonConfig = new FastJsonConfig();
fastJsonConfig.setSerializerFeatures(
SerializerFeature.WriteMapNullValue,
SerializerFeature.WriteNullStringAsEmpty,
SerializerFeature.WriteNullListAsEmpty,
SerializerFeature.WriteDateUseDateFormat);
SerializeConfig serializeConfig = SerializeConfig.globalInstance;
serializeConfig.put(BigInteger.class, ToStringSerializer.instance);
serializeConfig.put(Long.class, ToStringSerializer.instance);
serializeConfig.put(Long.TYPE, ToStringSerializer.instance);
fastJsonConfig.setSerializeConfig(serializeConfig);
fastConverter.setFastJsonConfig(fastJsonConfig);
converters.add(fastConverter);
}
}
@Data
public class Person {
private String userName;
private Integer age;
//使用fastjson的注解进行转换
@JSONField(format = "yyyy-MM-dd")
private Date birth;
private Pet pet;
}