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Package org.springframework.web.reactive.result

支持各种编程模型样式,包括调用不同类型的handles

img

handlerResultSupport.png

HandlerResultHandlerSupport

HandlerResultHandler的基类,支持内容协商和访问ReactiveAdapter注册表。

    public abstract class HandlerResultHandlerSupport implements Ordered {

private static final MediaType MEDIA_TYPE_APPLICATION_ALL = new MediaType("application");


private final RequestedContentTypeResolver contentTypeResolver;

private final ReactiveAdapterRegistry adapterRegistry;

private int order = LOWEST_PRECEDENCE;


protected HandlerResultHandlerSupport(RequestedContentTypeResolver contentTypeResolver,
ReactiveAdapterRegistry adapterRegistry) {

Assert.notNull(contentTypeResolver, "RequestedContentTypeResolver is required");
Assert.notNull(adapterRegistry, "ReactiveAdapterRegistry is required");
this.contentTypeResolver = contentTypeResolver;
this.adapterRegistry = adapterRegistry;
}


/**
* Return the configured {@link ReactiveAdapterRegistry}.
*/
public ReactiveAdapterRegistry getAdapterRegistry() {
return this.adapterRegistry;
}

/**
* Return the configured {@link RequestedContentTypeResolver}.
*/
public RequestedContentTypeResolver getContentTypeResolver() {
return this.contentTypeResolver;
}

/**
* Set the order for this result handler relative to others.
* <p>By default set to {@link Ordered#LOWEST_PRECEDENCE}, however see
* Javadoc of sub-classes which may change this default.
* @param order the order
*/
public void setOrder(int order) {
this.order = order;
}

@Override
public int getOrder() {
return this.order;
}


/**
* Get a {@code ReactiveAdapter} for the top-level return value type.
* @return the matching adapter or {@code null}
*/
@Nullable
protected ReactiveAdapter getAdapter(HandlerResult result) {
Class<?> returnType = result.getReturnType().getRawClass();
return getAdapterRegistry().getAdapter(returnType, result.getReturnValue());
}

/**
* Select the best media type for the current request through a content
* negotiation algorithm.
* @param exchange the current request
* @param producibleTypesSupplier the media types that can be produced for the current request
* @return the selected media type or {@code null}
*/
@Nullable
protected MediaType selectMediaType(ServerWebExchange exchange,
Supplier<List<MediaType>> producibleTypesSupplier) {

List<MediaType> acceptableTypes = getAcceptableTypes(exchange);
List<MediaType> producibleTypes = getProducibleTypes(exchange, producibleTypesSupplier);

Set<MediaType> compatibleMediaTypes = new LinkedHashSet<>();
for (MediaType acceptable : acceptableTypes) {
for (MediaType producible : producibleTypes) {
if (acceptable.isCompatibleWith(producible)) {
compatibleMediaTypes.add(selectMoreSpecificMediaType(acceptable, producible));
}
}
}

List<MediaType> result = new ArrayList<>(compatibleMediaTypes);
MediaType.sortBySpecificityAndQuality(result);

for (MediaType mediaType : result) {
if (mediaType.isConcrete()) {
return mediaType;
}
else if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION_ALL)) {
return MediaType.APPLICATION_OCTET_STREAM;
}
}

return null;
}

private List<MediaType> getAcceptableTypes(ServerWebExchange exchange) {
List<MediaType> mediaTypes = getContentTypeResolver().resolveMediaTypes(exchange);
return (mediaTypes.isEmpty() ? Collections.singletonList(MediaType.ALL) : mediaTypes);
}

@SuppressWarnings("unchecked")
private List<MediaType> getProducibleTypes(ServerWebExchange exchange,
Supplier<List<MediaType>> producibleTypesSupplier) {

Set<MediaType> mediaTypes = exchange.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
return (mediaTypes != null ? new ArrayList<>(mediaTypes) : producibleTypesSupplier.get());
}

private MediaType selectMoreSpecificMediaType(MediaType acceptable, MediaType producible) {
producible = producible.copyQualityValue(acceptable);
Comparator<MediaType> comparator = MediaType.SPECIFICITY_COMPARATOR;
return (comparator.compare(acceptable, producible) <= 0 ? acceptable : producible);
}

}

接口 View的Diagram

img

view.png

View

通过视图解析支持结果处理。

将HandlerResult呈现给HTTP响应的约定。

与Encoder相比,Encoder是一个单实例对象,并对给定类型的任何对象进行编码,因此,视图通常是通过名称来选择的,并使用ViewResolver来解析,例如将其与HTML模板匹配。此外,视图可以基于模型中包含的多个属性呈现。

视图还可以选择从模型中选择一个属性,使用任何现有的编码器来呈现替代媒体类型。

返回此视图支持的媒体类型列表,或空列表。
List<MediaType> getSupportedMediaTypes();

这个视图是否通过执行重定向来呈现。
default boolean isRedirectView() {
return false;
}

根据给定的HandlerResult呈现视图。实现可以访问和使用模型,或者仅在其中使用一个特定的属性。
Mono<Void> render(@Nullable Map<String, ?> model, @Nullable MediaType contentType, ServerWebExchange exchange);

AbstractView

View实现的基类。

public abstract class AbstractView implements View, ApplicationContextAware {

/** 在 bean factory 有名的RequestDataValueProcessor */
public static final String REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME = "requestDataValueProcessor";


/** 可用于子类的日志记录器 */
protected final Log logger = LogFactory.getLog(getClass());

private static final Object NO_VALUE = new Object();


private final List<MediaType> mediaTypes = new ArrayList<>(4);

private final ReactiveAdapterRegistry adapterRegistry;

private Charset defaultCharset = StandardCharsets.UTF_8;

@Nullable
private String requestContextAttribute;

@Nullable
private ApplicationContext applicationContext;


public AbstractView() {
this(new ReactiveAdapterRegistry());
}

public AbstractView(ReactiveAdapterRegistry registry) {
this.mediaTypes.add(ViewResolverSupport.DEFAULT_CONTENT_TYPE);
this.adapterRegistry = registry;
}


/**
* Set the supported media types for this view.
* Default is "text/html;charset=UTF-8".
*/
public void setSupportedMediaTypes(@Nullable List<MediaType> supportedMediaTypes) {
Assert.notEmpty(supportedMediaTypes, "MediaType List must not be empty");
this.mediaTypes.clear();
if (supportedMediaTypes != null) {
this.mediaTypes.addAll(supportedMediaTypes);
}
}

/**
* Return the configured media types supported by this view.
*/
@Override
public List<MediaType> getSupportedMediaTypes() {
return this.mediaTypes;
}

/**
* Set the default charset for this view, used when the
* {@linkplain #setSupportedMediaTypes(List) content type} does not contain one.
* Default is {@linkplain StandardCharsets#UTF_8 UTF 8}.
*/
public void setDefaultCharset(Charset defaultCharset) {
Assert.notNull(defaultCharset, "'defaultCharset' must not be null");
this.defaultCharset = defaultCharset;
}

/**
* Return the default charset, used when the
* {@linkplain #setSupportedMediaTypes(List) content type} does not contain one.
*/
public Charset getDefaultCharset() {
return this.defaultCharset;
}

/**
* Set the name of the RequestContext attribute for this view.
* Default is none.
*/
public void setRequestContextAttribute(@Nullable String requestContextAttribute) {
this.requestContextAttribute = requestContextAttribute;
}

/**
* Return the name of the RequestContext attribute, if any.
*/
@Nullable
public String getRequestContextAttribute() {
return this.requestContextAttribute;
}

@Override
public void setApplicationContext(@Nullable ApplicationContext applicationContext) {
this.applicationContext = applicationContext;
}

@Nullable
public ApplicationContext getApplicationContext() {
return this.applicationContext;
}

/**
* Obtain the ApplicationContext for actual use.
* @return the ApplicationContext (never {@code null})
* @throws IllegalStateException in case of no ApplicationContext set
*/
protected final ApplicationContext obtainApplicationContext() {
ApplicationContext applicationContext = getApplicationContext();
Assert.state(applicationContext != null, "No ApplicationContext");
return applicationContext;
}


/**
* Prepare the model to render.
* @param model Map with name Strings as keys and corresponding model
* objects as values (Map can also be {@code null} in case of empty model)
* @param contentType the content type selected to render with which should
* match one of the {@link #getSupportedMediaTypes() supported media types}.
* @param exchange the current exchange
* @return {@code Mono} to represent when and if rendering succeeds
*/
@Override
public Mono<Void> render(@Nullable Map<String, ?> model, @Nullable MediaType contentType,
ServerWebExchange exchange) {

if (logger.isTraceEnabled()) {
logger.trace("Rendering view with model " + model);
}

if (contentType != null) {
exchange.getResponse().getHeaders().setContentType(contentType);
}

return getModelAttributes(model, exchange).flatMap(mergedModel -> {
// Expose RequestContext?
if (this.requestContextAttribute != null) {
mergedModel.put(this.requestContextAttribute, createRequestContext(exchange, mergedModel));
}
return renderInternal(mergedModel, contentType, exchange);
});
}

/**
* Prepare the model to use for rendering.
* <p>The default implementation creates a combined output Map that includes
* model as well as static attributes with the former taking precedence.
*/
protected Mono<Map<String, Object>> getModelAttributes(@Nullable Map<String, ?> model,
ServerWebExchange exchange) {

int size = (model != null ? model.size() : 0);

Map<String, Object> attributes = new LinkedHashMap<>(size);
if (model != null) {
attributes.putAll(model);
}

return resolveAsyncAttributes(attributes).then(Mono.just(attributes));
}

/**
* By default, resolve async attributes supported by the
* {@link ReactiveAdapterRegistry} to their blocking counterparts.
* <p>View implementations capable of taking advantage of reactive types
* can override this method if needed.
* @return {@code Mono} for the completion of async attributes resolution
*/
protected Mono<Void> resolveAsyncAttributes(Map<String, Object> model) {

List<String> names = new ArrayList<>();
List<Mono<?>> valueMonos = new ArrayList<>();

for (Map.Entry<String, ?> entry : model.entrySet()) {
Object value = entry.getValue();
if (value == null) {
continue;
}
ReactiveAdapter adapter = this.adapterRegistry.getAdapter(null, value);
if (adapter != null) {
names.add(entry.getKey());
if (adapter.isMultiValue()) {
Flux<Object> fluxValue = Flux.from(adapter.toPublisher(value));
valueMonos.add(fluxValue.collectList().defaultIfEmpty(Collections.emptyList()));
}
else {
Mono<Object> monoValue = Mono.from(adapter.toPublisher(value));
valueMonos.add(monoValue.defaultIfEmpty(NO_VALUE));
}
}
}

if (names.isEmpty()) {
return Mono.empty();
}

return Mono.zip(valueMonos,
values -> {
for (int i=0; i < values.length; i++) {
if (values[i] != NO_VALUE) {
model.put(names.get(i), values[i]);
}
else {
model.remove(names.get(i));
}
}
return NO_VALUE;
})
.then();
}

/**
* Create a RequestContext to expose under the specified attribute name.
* <p>The default implementation creates a standard RequestContext instance
* for the given request and model. Can be overridden in subclasses for
* custom instances.
* @param exchange current exchange
* @param model combined output Map (never {@code null}),
* with dynamic values taking precedence over static attributes
* @return the RequestContext instance
* @see #setRequestContextAttribute
*/
protected RequestContext createRequestContext(ServerWebExchange exchange, Map<String, Object> model) {
return new RequestContext(exchange, model, obtainApplicationContext(), getRequestDataValueProcessor());
}

/**
* Return the {@link RequestDataValueProcessor} to use.
* <p>The default implementation looks in the {@link #getApplicationContext()
* Spring configuration} for a {@code RequestDataValueProcessor} bean with
* the name {@link #REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME}.
* @return the RequestDataValueProcessor, or null if there is none at the
* application context.
*/
@Nullable
protected RequestDataValueProcessor getRequestDataValueProcessor() {
ApplicationContext context = getApplicationContext();
if (context != null && context.containsBean(REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME)) {
return context.getBean(REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME, RequestDataValueProcessor.class);
}
return null;
}

/**
* Subclasses must implement this method to actually render the view.
* @param renderAttributes combined output Map (never {@code null}),
* with dynamic values taking precedence over static attributes
* @param contentType the content type selected to render with which should
* match one of the {@link #getSupportedMediaTypes() supported media types}.
*@param exchange current exchange @return {@code Mono} to represent when
* and if rendering succeeds
*/
protected abstract Mono<Void> renderInternal(Map<String, Object> renderAttributes,
@Nullable MediaType contentType, ServerWebExchange exchange);


@Override
public String toString() {
return getClass().getName();
}

}

ViewResolver

img

ViewResolver.png

Rendering

img

reanding.jpg

SimpleHandlerAdapter

HandlerAdapter,它允许使用普通的WebHandler与一般的DispatcherHandler一起使用。

public class SimpleHandlerAdapter implements HandlerAdapter {

private static final MethodParameter RETURN_TYPE;

static {
try {
Method method = WebHandler.class.getMethod("handle", ServerWebExchange.class);
RETURN_TYPE = new MethodParameter(method, -1);
}
catch (NoSuchMethodException ex) {
throw new IllegalStateException(
"Failed to initialize the return type for WebHandler: " + ex.getMessage());
}
}

//这个HandlerAdapter是否支持给定的handler。
@Override
public boolean supports(Object handler) {
return WebHandler.class.isAssignableFrom(handler.getClass());
}

//鼓励实现处理由调用handler所产生的异常,并在必要时返回代表错误响应的替代结果。
@Override
public Mono<HandlerResult> handle(ServerWebExchange exchange, Object handler) {
WebHandler webHandler = (WebHandler) handler;
Mono<Void> mono = webHandler.handle(exchange);
return mono.then(Mono.empty());
}

}

666. 彩蛋

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知识星球

文章目录
  1. 1. Package org.springframework.web.reactive.result
    1. 1.1. HandlerResultHandlerSupport
    2. 1.2. 接口 View的Diagram
      1. 1.2.1. View
      2. 1.2.2. AbstractView
    3. 1.3. ViewResolver
    4. 1.4. Rendering
    5. 1.5. SimpleHandlerAdapter
  2. 2. 666. 彩蛋