一、自定义 HttpMessageConverter
HttpMessageConverter 报文信息转化器，将请求报文转化成 Java 对象,或将 Java 对象转化为响应报文
HttpMessageConverter 提供了两个注解和两个类型：@RequestBody，@ResponseBody，RequestEntity，ResponseEntity
1.pom 依赖
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.7.2</version>
<relativePath/>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.26</version>
<optional>true</optional>
</dependency>
</dependencies>2.java
@Setter
@Getter
public class Pet {
private String name;
private Integer age;
}public class PetMessageConverter implements HttpMessageConverter<Pet> {
public final static String APPLICATION_MY_DATA = "application/my-data";
@Override
public boolean canRead(Class<?> clazz, MediaType mediaType) {
return clazz.isAssignableFrom(Pet.class);
}
@Override
public boolean canWrite(Class<?> clazz, MediaType mediaType) {
return clazz.isAssignableFrom(Pet.class);
}
@Override
public List<MediaType> getSupportedMediaTypes() {
return MediaType.parseMediaTypes(APPLICATION_MY_DATA);
}
@Override
public Pet read(Class<? extends Pet> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
// 请求体，形如：name:pet1, age:1
String body = StreamUtils.copyToString(inputMessage.getBody(), Charset.defaultCharset());
Map<String, String> map = Arrays.stream(body.split(","))
.map(item -> item.split(":"))
.collect(Collectors.toMap(pair -> pair[0].trim(), pair -> pair[1].trim()));
Pet pet = new Pet();
pet.setName(map.get("name"));
pet.setAge(Integer.valueOf(map.get("age")));
return pet;
}
@Override
public void write(Pet pet, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
OutputStream body = outputMessage.getBody();
String str = String.format("pet name: %s, pet age: %s", pet.getName(), pet.getAge());
body.write(str.getBytes());
}
}@Configuration(proxyBeanMethods = false)
public class PetWebMvcConfig implements WebMvcConfigurer {
@Override
public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(new PetMessageConverter());
}
}@RestController
public class IndexController {
@PostMapping(value = "/pet1", produces = {PetMessageConverter.APPLICATION_MY_DATA})
public Pet pet1(@RequestBody Pet request) {
Pet res = new Pet();
res.setName(request.getName());
res.setAge(request.getAge());
return res;
}
}@SpringBootApplication
public class WebBoot {
public static void main(String[] args) {
SpringApplication.run(WebBoot.class, args);
}
}3.测试
zxm@zxm-pc:~$ curl -X POST -H "Content-Type: application/my-data" -d 'name:pet11, age:11' http://localhost:8080/pet1
pet name: pet11, pet age: 11二、原理
1.加载 WebMvcAutoConfiguration
spring-boot-autoconfigure-2.7.2.jar 下有文件
org.springframework.boot.autoconfigure.AutoConfiguration.imports，内有：
根据 META-INF 下文件，会加载 AopAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration2.注册 RequestMappingHandlerAdapter
EnableWebMvcConfiguration 继承 DelegatingWebMvcConfiguration，DelegatingWebMvcConfiguration 继承 WebMvcConfigurationSupport
注册 EnableWebMvcConfiguration 的时候，会调用 setConfigurers 方法，
把 WebMvcConfigurer 的 bean（此时会找到 WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter 和 自定义的 PetWebMvcConfig），赋值到 configurers 中
// WebMvcAutoConfiguration.java
@AutoConfiguration(after = { DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
ValidationAutoConfiguration.class })
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
public class WebMvcAutoConfiguration {
...
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(WebProperties.class)
public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {
...
@Bean
@Override
public RequestMappingHandlerAdapter requestMappingHandlerAdapter(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcValidator") Validator validator) {
RequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter(contentNegotiationManager,
conversionService, validator);
adapter.setIgnoreDefaultModelOnRedirect(
this.mvcProperties == null || this.mvcProperties.isIgnoreDefaultModelOnRedirect());
return adapter;
}
...
}
...
}// DelegatingWebMvcConfiguration.java
@Configuration(proxyBeanMethods = false)
public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
...
@Autowired(required = false)
public void setConfigurers(List<WebMvcConfigurer> configurers) {
if (!CollectionUtils.isEmpty(configurers)) {
this.configurers.addWebMvcConfigurers(configurers);
}
}
...
}创建 RequestMappingHandlerAdapter，为 RequestMappingHandlerAdapter 赋值 messageConverters
// WebMvcConfigurationSupport.java
public class WebMvcConfigurationSupport implements ApplicationContextAware, ServletContextAware {
...
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcValidator") Validator validator) {
RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();
adapter.setContentNegotiationManager(contentNegotiationManager);
adapter.setMessageConverters(getMessageConverters());
adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer(conversionService, validator));
adapter.setCustomArgumentResolvers(getArgumentResolvers());
adapter.setCustomReturnValueHandlers(getReturnValueHandlers());
if (jackson2Present) {
adapter.setRequestBodyAdvice(Collections.singletonList(new JsonViewRequestBodyAdvice()));
adapter.setResponseBodyAdvice(Collections.singletonList(new JsonViewResponseBodyAdvice()));
}
AsyncSupportConfigurer configurer = getAsyncSupportConfigurer();
if (configurer.getTaskExecutor() != null) {
adapter.setTaskExecutor(configurer.getTaskExecutor());
}
if (configurer.getTimeout() != null) {
adapter.setAsyncRequestTimeout(configurer.getTimeout());
}
adapter.setCallableInterceptors(configurer.getCallableInterceptors());
adapter.setDeferredResultInterceptors(configurer.getDeferredResultInterceptors());
return adapter;
}
protected final List<HandlerMethodArgumentResolver> getArgumentResolvers() {
if (this.argumentResolvers == null) {
this.argumentResolvers = new ArrayList<>();
addArgumentResolvers(this.argumentResolvers);
}
return this.argumentResolvers;
}
...
}RequestMappingHandlerAdapter 的 afterPropertiesSet 会赋值默认的 argumentResolvers、initBinderArgumentResolvers、returnValueHandlers
argumentResolvers 为 RequestResponseBodyMethodProcessor（处理 @RequestBody）、RequestPartMethodArgumentResolver（处理 @RequestPart）、HttpEntityMethodProcessor（处理 HttpEntity、RequestEntity
），会把 messageConverters 传递其中
returnValueHandlers 为 ResponseBodyEmitterReturnValueHandler（处理 ResponseEntity）、HttpEntityMethodProcessor（处理 HttpEntity）、RequestResponseBodyMethodProcessor（处理 @RequestBody），会把 messageConverters 传递其中
// RequestMappingHandlerAdapter.java
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
...
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>(30);
// Annotation-based argument resolution
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
resolvers.add(new RequestParamMapMethodArgumentResolver());
resolvers.add(new PathVariableMethodArgumentResolver());
resolvers.add(new PathVariableMapMethodArgumentResolver());
resolvers.add(new MatrixVariableMethodArgumentResolver());
resolvers.add(new MatrixVariableMapMethodArgumentResolver());
resolvers.add(new ServletModelAttributeMethodProcessor(false));
resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));
resolvers.add(new RequestHeaderMapMethodArgumentResolver());
resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new SessionAttributeMethodArgumentResolver());
resolvers.add(new RequestAttributeMethodArgumentResolver());
// Type-based argument resolution
resolvers.add(new ServletRequestMethodArgumentResolver());
resolvers.add(new ServletResponseMethodArgumentResolver());
resolvers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RedirectAttributesMethodArgumentResolver());
resolvers.add(new ModelMethodProcessor());
resolvers.add(new MapMethodProcessor());
resolvers.add(new ErrorsMethodArgumentResolver());
resolvers.add(new SessionStatusMethodArgumentResolver());
resolvers.add(new UriComponentsBuilderMethodArgumentResolver());
if (KotlinDetector.isKotlinPresent()) {
resolvers.add(new ContinuationHandlerMethodArgumentResolver());
}
// Custom arguments
if (getCustomArgumentResolvers() != null) {
resolvers.addAll(getCustomArgumentResolvers());
}
// Catch-all
resolvers.add(new PrincipalMethodArgumentResolver());
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
resolvers.add(new ServletModelAttributeMethodProcessor(true));
return resolvers;
}
private List<HandlerMethodArgumentResolver> getDefaultInitBinderArgumentResolvers() {
List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>(20);
// Annotation-based argument resolution
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
resolvers.add(new RequestParamMapMethodArgumentResolver());
resolvers.add(new PathVariableMethodArgumentResolver());
resolvers.add(new PathVariableMapMethodArgumentResolver());
resolvers.add(new MatrixVariableMethodArgumentResolver());
resolvers.add(new MatrixVariableMapMethodArgumentResolver());
resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new SessionAttributeMethodArgumentResolver());
resolvers.add(new RequestAttributeMethodArgumentResolver());
// Type-based argument resolution
resolvers.add(new ServletRequestMethodArgumentResolver());
resolvers.add(new ServletResponseMethodArgumentResolver());
// Custom arguments
if (getCustomArgumentResolvers() != null) {
resolvers.addAll(getCustomArgumentResolvers());
}
// Catch-all
resolvers.add(new PrincipalMethodArgumentResolver());
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
return resolvers;
}
private List<HandlerMethodReturnValueHandler> getDefaultReturnValueHandlers() {
List<HandlerMethodReturnValueHandler> handlers = new ArrayList<>(20);
// Single-purpose return value types
handlers.add(new ModelAndViewMethodReturnValueHandler());
handlers.add(new ModelMethodProcessor());
handlers.add(new ViewMethodReturnValueHandler());
handlers.add(new ResponseBodyEmitterReturnValueHandler(getMessageConverters(),
this.reactiveAdapterRegistry, this.taskExecutor, this.contentNegotiationManager));
handlers.add(new StreamingResponseBodyReturnValueHandler());
handlers.add(new HttpEntityMethodProcessor(getMessageConverters(),
this.contentNegotiationManager, this.requestResponseBodyAdvice));
handlers.add(new HttpHeadersReturnValueHandler());
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));
// Annotation-based return value types
handlers.add(new ServletModelAttributeMethodProcessor(false));
handlers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(),
this.contentNegotiationManager, this.requestResponseBodyAdvice));
// Multi-purpose return value types
handlers.add(new ViewNameMethodReturnValueHandler());
handlers.add(new MapMethodProcessor());
// Custom return value types
if (getCustomReturnValueHandlers() != null) {
handlers.addAll(getCustomReturnValueHandlers());
}
// Catch-all
if (!CollectionUtils.isEmpty(getModelAndViewResolvers())) {
handlers.add(new ModelAndViewResolverMethodReturnValueHandler(getModelAndViewResolvers()));
}
else {
handlers.add(new ServletModelAttributeMethodProcessor(true));
}
return handlers;
}
...
}3.解析请求参数和处理返回值
3.1解析请求参数
找到匹配的 argumentResolver 是 RequestResponseBodyMethodProcessor
调用 ((HttpMessageConverter
// HandlerMethodArgumentResolverComposite.java
@Override
@Nullable
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
...
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
// RequestResponseBodyMethodProcessor.java
@Override
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
parameter = parameter.nestedIfOptional();
Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());
String name = Conventions.getVariableNameForParameter(parameter);
...
return adaptArgumentIfNecessary(arg, parameter);
}
@Override
protected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter parameter,
Type paramType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
...
Object arg = readWithMessageConverters(inputMessage, parameter, paramType);
...
return arg;
}
@Nullable
protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter parameter,
Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
...
EmptyBodyCheckingHttpInputMessage message = null;
try {
message = new EmptyBodyCheckingHttpInputMessage(inputMessage);
for (HttpMessageConverter<?> converter : this.messageConverters) {
Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
GenericHttpMessageConverter<?> genericConverter =
(converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter<?>) converter : null);
if (genericConverter != null ? genericConverter.canRead(targetType, contextClass, contentType) :
(targetClass != null && converter.canRead(targetClass, contentType))) {
if (message.hasBody()) {
HttpInputMessage msgToUse =
getAdvice().beforeBodyRead(message, parameter, targetType, converterType);
body = (genericConverter != null ? genericConverter.read(targetType, contextClass, msgToUse) :
((HttpMessageConverter<T>) converter).read(targetClass, msgToUse));
body = getAdvice().afterBodyRead(body, msgToUse, parameter, targetType, converterType);
}
else {
body = getAdvice().handleEmptyBody(null, message, parameter, targetType, converterType);
}
break;
}
}
}
...
return body;
}3.2处理返回值
找到匹配的 returnValueHandler 是 RequestResponseBodyMethodProcessor
调用 ((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage) 处理返回值
// HandlerMethodReturnValueHandlerComposite.java
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
...
handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
}// RequestResponseBodyMethodProcessor.java
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
mavContainer.setRequestHandled(true);
ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);
// Try even with null return value. ResponseBodyAdvice could get involved.
writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
}
protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
Object body;
Class<?> valueType;
Type targetType;
if (value instanceof CharSequence) {
body = value.toString();
valueType = String.class;
targetType = String.class;
}
else {
body = value;
valueType = getReturnValueType(body, returnType);
targetType = GenericTypeResolver.resolveType(getGenericType(returnType), returnType.getContainingClass());
}
...
if (selectedMediaType != null) {
selectedMediaType = selectedMediaType.removeQualityValue();
for (HttpMessageConverter<?> converter : this.messageConverters) {
GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
(GenericHttpMessageConverter<?>) converter : null);
if (genericConverter != null ?
((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
converter.canWrite(valueType, selectedMediaType)) {
body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
(Class<? extends HttpMessageConverter<?>>) converter.getClass(),
inputMessage, outputMessage);
if (body != null) {
Object theBody = body;
LogFormatUtils.traceDebug(logger, traceOn ->
"Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
addContentDispositionHeader(inputMessage, outputMessage);
if (genericConverter != null) {
genericConverter.write(body, targetType, selectedMediaType, outputMessage);
}
else {
((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Nothing to write: null body");
}
}
return;
}
}
}
...
}