前言
resourceHandlerMapping提供了资源的访问。
一、resourceHandlerMapping
@Nullable
public HandlerMapping resourceHandlerMapping(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {
Assert.state(this.applicationContext != null, "No ApplicationContext set");
Assert.state(this.servletContext != null, "No ServletContext set");
PathMatchConfigurer pathConfig = getPathMatchConfigurer();
ResourceHandlerRegistry registry = new ResourceHandlerRegistry(this.applicationContext,
this.servletContext, contentNegotiationManager, pathConfig.getUrlPathHelper());
//注册ResourceHandler
addResourceHandlers(registry);
//获取handlerMapping ，这里是SimpleUrlHandlerMapping，handler是ResourceHttpRequestHandler
AbstractHandlerMapping handlerMapping = registry.getHandlerMapping();
if (handlerMapping == null) {
return null;
}
if (pathConfig.getPatternParser() != null) {
handlerMapping.setPatternParser(pathConfig.getPatternParser());
}
else {
handlerMapping.setUrlPathHelper(pathConfig.getUrlPathHelperOrDefault());
handlerMapping.setPathMatcher(pathConfig.getPathMatcherOrDefault());
}
//拦截器
handlerMapping.setInterceptors(getInterceptors(conversionService, resourceUrlProvider));
//跨域
handlerMapping.setCorsConfigurations(getCorsConfigurations());
return handlerMapping;
}
二、ResourceHttpRequestHandler
接着上一步中registry.getHandlerMapping()分析
（1）getHandlerMapping( )
protected AbstractHandlerMapping getHandlerMapping() {
if (this.registrations.isEmpty()) {
return null;
}
Map<String, HttpRequestHandler> urlMap = new LinkedHashMap<>();
for (ResourceHandlerRegistration registration : this.registrations) {
for (String pathPattern : registration.getPathPatterns()) {
//获取ResourceHttpRequestHandler
ResourceHttpRequestHandler handler = registration.getRequestHandler();
if (this.pathHelper != null) {
handler.setUrlPathHelper(this.pathHelper);
}
if (this.contentNegotiationManager != null) {
handler.setContentNegotiationManager(this.contentNegotiationManager);
}
handler.setServletContext(this.servletContext);
handler.setApplicationContext(this.applicationContext);
try {
//调用afterPropertiesSet()
handler.afterPropertiesSet();
}
catch (Throwable ex) {
throw new BeanInitializationException("Failed to init ResourceHttpRequestHandler", ex);
}
urlMap.put(pathPattern, handler);
}
}
//构建SimpleUrlHandlerMapping
return new SimpleUrlHandlerMapping(urlMap, this.order);
}
（2）getRequestHandler( )
protected ResourceHttpRequestHandler getRequestHandler() {
//创建ResourceHttpRequestHandler
ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();
if (this.resourceChainRegistration != null) {
//填充属性
handler.setResourceResolvers(this.resourceChainRegistration.getResourceResolvers());
handler.setResourceTransformers(this.resourceChainRegistration.getResourceTransformers());
}
//locationValues保存着资源的路径
handler.setLocationValues(this.locationValues);
handler.setLocations(this.locationsResources);
if (this.cacheControl != null) {
handler.setCacheControl(this.cacheControl);
}
else if (this.cachePeriod != null) {
handler.setCacheSeconds(this.cachePeriod);
}
handler.setUseLastModified(this.useLastModified);
return handler;
}
三、HttpRequestHandlerAdapter
（1）handle( )
HttpRequestHandlerAdapter.java
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
((HttpRequestHandler) handler).handleRequest(request, response);
return null;
}
（2）handleRequest( )
ResourceHttpRequestHandler.java
public void handleRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// For very general mappings (e.g. "/") we need to check 404 first
//获取请求资源
Resource resource = getResource(request);
if (resource == null) {
logger.debug("Resource not found");
response.sendError(HttpServletResponse.SC_NOT_FOUND);
return;
}
if (HttpMethod.OPTIONS.matches(request.getMethod())) {
response.setHeader("Allow", getAllowHeader());
return;
}
// Supported methods and required session
checkRequest(request);
// Header phase
//校验资源有没有变化过
if (isUseLastModified() && new ServletWebRequest(request, response).checkNotModified(resource.lastModified())) {
logger.trace("Resource not modified");
return;
}
// Apply cache settings, if any
prepareResponse(response);
// Check the media type for the resource
MediaType mediaType = getMediaType(request, resource);
setHeaders(response, resource, mediaType);
// Content phase
ServletServerHttpResponse outputMessage = new ServletServerHttpResponse(response);
if (request.getHeader(HttpHeaders.RANGE) == null) {
Assert.state(this.resourceHttpMessageConverter != null, "Not initialized");
this.resourceHttpMessageConverter.write(resource, mediaType, outputMessage);
}
else {
Assert.state(this.resourceRegionHttpMessageConverter != null, "Not initialized");
ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(request);
try {
List<HttpRange> httpRanges = inputMessage.getHeaders().getRange();
response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
this.resourceRegionHttpMessageConverter.write(
HttpRange.toResourceRegions(httpRanges, resource), mediaType, outputMessage);
}
catch (IllegalArgumentException ex) {
response.setHeader(HttpHeaders.CONTENT_RANGE, "bytes */" + resource.contentLength());
response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
}
}
}
（3）getResource( )
ResourceHttpRequestHandler.java
@Nullable
protected Resource getResource(HttpServletRequest request) throws IOException {
String path = (String) request.getAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE);
if (path == null) {
throw new IllegalStateException("Required request attribute '" +
HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE + "' is not set");
}
//处理路径
path = processPath(path);
if (!StringUtils.hasText(path) || isInvalidPath(path)) {
return null;
}
if (isInvalidEncodedPath(path)) {
return null;
}
Assert.notNull(this.resolverChain, "ResourceResolverChain not initialized.");
Assert.notNull(this.transformerChain, "ResourceTransformerChain not initialized.");
//根据设置的路径找到资源
Resource resource = this.resolverChain.resolveResource(request, path, getLocations());
if (resource != null) {
resource = this.transformerChain.transform(request, resource);
}
return resource;
}
（4）resolveResource( )
DefaultResourceResolverChain.java
public Resource resolveResource(
@Nullable HttpServletRequest request, String requestPath, List<? extends Resource> locations) {
return (this.resolver != null && this.nextChain != null ?
this.resolver.resolveResource(request, requestPath, locations, this.nextChain) : null);
}
（5）最终通过PathResourceResolver获取请求资源
private Resource getResource(String resourcePath, @Nullable HttpServletRequest request,
List<? extends Resource> locations) {
for (Resource location : locations) {
try {
//
String pathToUse = encodeOrDecodeIfNecessary(resourcePath, request, location);
Resource resource = getResource(pathToUse, location);
if (resource != null) {
return resource;
}
}
catch (IOException ex) {
if (logger.isDebugEnabled()) {
String error = "Skip location [" + location + "] due to error";
if (logger.isTraceEnabled()) {
logger.trace(error, ex);
}
else {
logger.debug(error + ": " + ex.getMessage());
}
}
}
}
return null;
}
（6）getResource( )
protected Resource getResource(String resourcePath, Resource location) throws IOException {
Resource resource = location.createRelative(resourcePath);
if (resource.isReadable()) {
if (checkResource(resource, location)) {
return resource;
}
else if (logger.isWarnEnabled()) {
Resource[] allowedLocations = getAllowedLocations();
logger.warn("Resource path \"" + resourcePath + "\" was successfully resolved " +
"but resource \"" + resource.getURL() + "\" is neither under the " +
"current location \"" + location.getURL() + "\" nor under any of the " +
"allowed locations " + (allowedLocations != null ? Arrays.asList(allowedLocations) : "[]"));
}
}
return null;
}
（7）createRelative( )
通过ClassPathResource获取资源
public Resource createRelative(String relativePath) {
String pathToUse = StringUtils.applyRelativePath(this.path, relativePath);
return (this.clazz != null ? new ClassPathResource(pathToUse, this.clazz) :
new ClassPathResource(pathToUse, this.classLoader));
}
四、示例
@Configuration
public class ResourceHandlerConfig implements WebMvcConfigurer {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.
addResourceHandler("/swagger-ui/**")
.addResourceLocations("classpath:/META-INF/resources/webjars/springfox-swagger-ui/")
.resourceChain(false);
}
}
当访问以/swagger-ui/开头的路径下资源时，会在classpath:/META-INF/resources/webjars/springfox-swagger-ui/路径下查找资源。
总结
通过addResourceHandlers注册资源，通过ClassPathResource获取资源。