一、為什么會出現(xiàn)跨域問題

二、什么是跨域

三、非同源限制

1. 無法讀取非同源網(wǎng)頁的 Cookie、LocalStorage 和 IndexedDB
2. 無法接觸非同源網(wǎng)頁的 DOM
3. 無法向非同源地址發(fā)送 AJAX 請求
4. 如果您正在學習Spring Boot，那么推薦一個連載多年還在繼續(xù)更新的免費教程：http://blog.didispace.com/spring-boot-learning-2x/

四、java 后端 實現(xiàn) CORS 跨域請求的方式

1. 返回新的CorsFilter
2. 重寫 WebMvcConfigurer
3. 使用注解 @CrossOrigin
4. 手動設置響應頭 (HttpServletResponse)
5. 自定 web filter 實現(xiàn)跨域

• CorFilter / WebMvConfigurer / @CrossOrigin 需要 SpringMVC 4.2以上版本才支持，對應springBoot 1.3版本以上
• 上面前兩種方式屬于全局 CORS 配置，后兩種屬于局部 CORS配置。如果使用了局部跨域是會覆蓋全局跨域的規(guī)則，所以可以通過 @CrossOrigin 注解來進行細粒度更高的跨域資源控制。
• 其實無論哪種方案，最終目的都是修改響應頭，向響應頭中添加瀏覽器所要求的數(shù)據(jù)，進而實現(xiàn)跨域

1.返回新的 CorsFilter(全局跨域)

@Configuration
public?class?GlobalCorsConfig?{
????@Bean
????public?CorsFilter?corsFilter()?{
????????//1.?添加?CORS配置信息
????????CorsConfiguration?config?=?new?CorsConfiguration();
????????//放行哪些原始域
????????config.addAllowedOrigin("*");
????????//是否發(fā)送?Cookie
????????config.setAllowCredentials(true);
????????//放行哪些請求方式
????????config.addAllowedMethod("*");
????????//放行哪些原始請求頭部信息
????????config.addAllowedHeader("*");
????????//暴露哪些頭部信息
????????config.addExposedHeader("*");
????????//2.?添加映射路徑
????????UrlBasedCorsConfigurationSource?corsConfigurationSource?=?new?UrlBasedCorsConfigurationSource();
????????corsConfigurationSource.registerCorsConfiguration("/**",config);
????????//3.?返回新的CorsFilter
????????return?new?CorsFilter(corsConfigurationSource);
????}
}

2. 重寫 WebMvcConfigurer(全局跨域)

@Configuration
public?class?CorsConfig?implements?WebMvcConfigurer?{
????@Override
????public?void?addCorsMappings(CorsRegistry?registry)?{
????????registry.addMapping("/**")
????????????????//是否發(fā)送Cookie
????????????????.allowCredentials(true)
????????????????//放行哪些原始域
????????????????.allowedOrigins("*")
????????????????.allowedMethods(new?String[]{"GET",?"POST",?"PUT",?"DELETE"})
????????????????.allowedHeaders("*")
????????????????.exposedHeaders("*");
????}
}

3. 使用注解 (局部跨域)

@RestController
@CrossOrigin(origins?=?"*")
public?class?HelloController?{
????@RequestMapping("/hello")
????public?String?hello()?{
????????return?"hello?world";
????}
}

@RequestMapping("/hello")
????@CrossOrigin(origins?=?"*")
?????//@CrossOrigin(value?=?"http://localhost:8081")?//指定具體ip允許跨域
????public?String?hello()?{
????????return?"hello?world";
????}

4. 手動設置響應頭(局部跨域)

@RequestMapping("/index")
public?String?index(HttpServletResponse?response)?{
????response.addHeader("Access-Allow-Control-Origin","*");
????return?"index";
}

5. 使用自定義filter實現(xiàn)跨域

package?com.mesnac.aop;

import?java.io.IOException;
import?javax.servlet.Filter;
import?javax.servlet.FilterChain;
import?javax.servlet.FilterConfig;
import?javax.servlet.ServletException;
import?javax.servlet.ServletRequest;
import?javax.servlet.ServletResponse;
import?javax.servlet.http.HttpServletResponse;
import?org.springframework.stereotype.Component;
@Component
public?class?MyCorsFilter?implements?Filter?{
??public?void?doFilter(ServletRequest?req,?ServletResponse?res,?FilterChain?chain)?throws?IOException,?ServletException?{
????HttpServletResponse?response?=?(HttpServletResponse)?res;
????response.setHeader("Access-Control-Allow-Origin",?"*");
????response.setHeader("Access-Control-Allow-Methods",?"POST,?GET,?OPTIONS,?DELETE");
????response.setHeader("Access-Control-Max-Age",?"3600");
????response.setHeader("Access-Control-Allow-Headers",?"x-requested-with,content-type");
????chain.doFilter(req,?res);
??}
??public?void?init(FilterConfig?filterConfig)?{}
??public?void?destroy()?{}
}

<filter>
?<filter-name>CorsFilterfilter-name>
?<filter-class>com.mesnac.aop.MyCorsFilterfilter-class>
filter>
<filter-mapping>
?<filter-name>CorsFilterfilter-name>
?<url-pattern>/*url-pattern>
filter-mapping>