private boolean allowCircularReferences;

/**
 * Sets whether to allow circular references between beans and automatically try to
 * resolve them. Defaults to {@code false}.
 * @param allowCircularReferences if circular references are allowed
 * @since 2.6.0
 * @see AbstractAutowireCapableBeanFactory#setAllowCircularReferences(boolean)
 */
public void setAllowCircularReferences(boolean allowCircularReferences) {
	this.allowCircularReferences = allowCircularReferences;
}

BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
	if (!isAllowBeanDefinitionOverriding()) {
		throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
	}
	
  // ...
	this.beanDefinitionMap.put(beanName, beanDefinition);
}

private boolean allowBeanDefinitionOverriding;

/**
 * Sets if bean definition overriding, by registering a definition with the same name
 * as an existing definition, should be allowed. Defaults to {@code false}.
 * @param allowBeanDefinitionOverriding if overriding is allowed
 * @since 2.1.0
 * @see DefaultListableBeanFactory#setAllowBeanDefinitionOverriding(boolean)
 */
public void setAllowBeanDefinitionOverriding(boolean allowBeanDefinitionOverriding) {
	this.allowBeanDefinitionOverriding = allowBeanDefinitionOverriding;
}

**spring.mvc.pathmatch.matching-strategy=***ANT_PATH_MATCHER*

/**
	 * Validate that when {@link #setAllowCredentials allowCredentials} is {@code true},
	 * {@link #setAllowedOrigins allowedOrigins} does not contain the special
	 * value {@code "*"} since in that case the "Access-Control-Allow-Origin"
	 * cannot be set to {@code "*"}.
	 * @throws IllegalArgumentException if the validation fails
	 * @since 5.3
	 */
	public void validateAllowCredentials() {
		if (this.allowCredentials == Boolean.TRUE &&
				this.allowedOrigins != null && this.allowedOrigins.contains(ALL)) {

			throw new IllegalArgumentException(
					"When allowCredentials is true, allowedOrigins cannot contain the special value \\"*\\" " +
							"since that cannot be set on the \\"Access-Control-Allow-Origin\\" response header. " +
							"To allow credentials to a set of origins, list them explicitly " +
							"or consider using \\"allowedOriginPatterns\\" instead.");
		}
	}

@Configuration
public class CorsConfig implements WebMvcConfigurer {

    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")    // 允許跨域訪問(wèn)的路徑
                .allowedOriginPatterns("*")    // 允許跨域訪問(wèn)的源
    }
}

/**
 * Alternative to {@link #setAllowedOrigins} that supports more flexible
 * origins patterns with "*" anywhere in the host name in addition to port
 * lists. Examples:
 * <ul>
 * <li>{@literal https://*.domain1.com} -- domains ending with domain1.com
 * <li>{@literal https://*.domain1.com:[8080,8081]} -- domains ending with
 * domain1.com on port 8080 or port 8081
 * <li>{@literal https://*.domain1.com:[*]} -- domains ending with
 * domain1.com on any port, including the default port
 * </ul>
 * <p>In contrast to {@link #setAllowedOrigins(List) allowedOrigins} which
 * only supports "*" and cannot be used with {@code allowCredentials}, when
 * an allowedOriginPattern is matched, the {@code Access-Control-Allow-Origin}
 * response header is set to the matched origin and not to {@code "*"} nor
 * to the pattern. Therefore allowedOriginPatterns can be used in combination
 * with {@link #setAllowCredentials} set to {@code true}.
 * <p>By default this is not set.
 * @since 5.3
 */
public CorsConfiguration setAllowedOriginPatterns(@Nullable List<String> allowedOriginPatterns) {
	if (allowedOriginPatterns == null) {
		this.allowedOriginPatterns = null;
	}
	else {
		this.allowedOriginPatterns = new ArrayList<>(allowedOriginPatterns.size());
		for (String patternValue : allowedOriginPatterns) {
			addAllowedOriginPattern(patternValue);
		}
	}
	return this;
}

// 5.3之前
@Override
public boolean isReadable() {
	try {
		URL url = getURL();
    // file/vfsfile/vfs開(kāi)頭的url
		if (ResourceUtils.isFileURL(url)) {
			// Proceed with file system resolution
			File file = getFile();
			return (file.canRead() && !file.isDirectory());
		}
		else {
			return true;
		}
	}
	catch (IOException ex) {
		return false;
	}
}

@Override
public boolean isReadable() {
	URL url = resolveURL();
	return (url != null && checkReadable(url));
}

boolean checkReadable(URL url) {
	try {
    // file/vfsfile/vfs開(kāi)頭的url
		if (ResourceUtils.isFileURL(url)) {
			// Proceed with file system resolution
			File file = getFile();
			return (file.canRead() && !file.isDirectory());
		}
		else {
			// Try InputStream resolution for jar resources
			URLConnection con = url.openConnection();
			customizeConnection(con);
			if (con instanceof HttpURLConnection) {
				HttpURLConnection httpCon = (HttpURLConnection) con;
				httpCon.setRequestMethod("HEAD");
				int code = httpCon.getResponseCode();
				if (code != HttpURLConnection.HTTP_OK) {
					httpCon.disconnect();
					return false;
				}
			}
			long contentLength = con.getContentLengthLong();
			if (contentLength > 0) {
				return true;
			}
			else if (contentLength == 0) {
				// Empty file or directory -> not considered readable...
				return false;
			}
			else {
				// Fall back to stream existence: can we open the stream?
				getInputStream().close();
				return true;
			}
		}
	}
	catch (IOException ex) {
		return false;
	}
}

/**
 * Returns either {@link #getPathPatternsCondition()} or
 * {@link #getPatternsCondition()} depending on which is not null.
 * @since 5.3
 */
@SuppressWarnings("unchecked")
public <T> RequestCondition<T> getActivePatternsCondition() {
	if (this.pathPatternsCondition != null) {
		return (RequestCondition<T>) this.pathPatternsCondition;
	}
	else if (this.patternsCondition != null) {
		return (RequestCondition<T>) this.patternsCondition;
	}
	else {
		// Already checked in the constructor...
		throw new IllegalStateException();
	}
}