曾經開發人臉識別的token的批量服務的時候遇到了跨域問題，當時也不之所以然，畢竟前後端分離的架構，遇到資源來自不同的域是在所難免的，但是前端提出了這個問題之後，查找了之前的解決方案使用了
WebMvcConfigurerAdapter來解決的，具體的使用如下，只需要在controller層新增上就可以，這裡代表的意思是CorsRegistry 支援任意的路徑任意方法的跨域訪問

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
public class CustomCorsConfigurationService extends WebMvcConfigurerAdapter {
	@Override
	public void addCorsMappings(CorsRegistry registry) {
		registry.addMapping("/**").allowedOrigins("*").allowedMethods("*").allowCredentials(true);
	}
}
 

然後查看了WebMvcConfigurerAdapter的原始碼瞭解關於跨域的這個方法addCorsMappings(CorsRegistry registry)的實現，就一個空方法

/**
	 * {@inheritDoc}
	 * <p>This implementation is empty.
	 */
	@Override
	public void addCorsMappings(CorsRegistry registry) {
	}

然後查找了CrosRegistry的定義程式碼

/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.config.annotation;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.springframework.web.cors.CorsConfiguration;

/**
 * {@code CorsRegistry} assists with the registration of {@link CorsConfiguration}
 * mapped to a path pattern.
 *
 * @author Sebastien Deleuze
 * @since 4.2
 * @see CorsRegistration
 */
public class CorsRegistry {

	private final List<CorsRegistration> registrations = new ArrayList<CorsRegistration>();


	/**
	 * Enable cross-origin request handling for the specified path pattern.
	 * <p>Exact path mapping URIs (such as {@code "/admin"}) are supported as
	 * well as Ant-style path patterns (such as {@code "/admin/**"}).
	 * <p>By default, all origins, all headers, credentials and {@code GET},
	 * {@code HEAD}, and {@code POST} methods are allowed, and the max age
	 * is set to 30 minutes.
	 * @param pathPattern the path pattern to enable CORS handling for
	 * @return CorsRegistration the corresponding registration object,
	 * allowing for further fine-tuning
	 */
	public CorsRegistration addMapping(String pathPattern) {
		CorsRegistration registration = new CorsRegistration(pathPattern);
		this.registrations.add(registration);
		return registration;
	}

	/**
	 * Return the registered {@link CorsConfiguration} objects,
	 * keyed by path pattern.
	 */
	protected Map<String, CorsConfiguration> getCorsConfigurations() {
		Map<String, CorsConfiguration> configs = new LinkedHashMap<String, CorsConfiguration>(this.registrations.size());
		for (CorsRegistration registration : this.registrations) {
			configs.put(registration.getPathPattern(), registration.getCorsConfiguration());
		}
		return configs;
	}

}

 

從CorsRegistry看到核心邏輯來自CorsRegistration的定義，注意註釋的程式碼
// Same implicit default values as the @CrossOrigin annotation + allows simple methods
如果不寫這個自定義的CrosRegistry也可以通過註解@CrossOrigin來實現

/**
	 * Create a new {@link CorsRegistration} that allows all origins, headers, and
	 * credentials for {@code GET}, {@code HEAD}, and {@code POST} requests with
	 * max age set to 1800 seconds (30 minutes) for the specified path.
	 * @param pathPattern the path that the CORS configuration should apply to;
	 * exact path mapping URIs (such as {@code "/admin"}) are supported as well
	 * as Ant-style path patterns (such as {@code "/admin/**"}).
	 */
	public CorsRegistration(String pathPattern) {
		this.pathPattern = pathPattern;
		// Same implicit default values as the @CrossOrigin annotation + allows simple methods
		this.config = new CorsConfiguration().applyPermitDefaultValues();
	}