SpringMVC 4.2 对跨域的支持

Cross-origin resource sharing (CORS) is a W3C specification implemented by most browsers that allows you to specify in a flexible way what kind of cross domain requests are authorized, instead of using some less secure and less powerful approaches like IFRAME or JSONP. As of version 4.2, Spring MVC supports CORS out of the box. Using controller method CORS configuration with @CrossOrigin annotations in your Spring Boot application does not require any specific configuration. Global CORS configuration can be defined by registering a WebMvcConfigurer bean with a customized addCorsMappings(CorsRegistry) method:

@Configuration
public class MyConfiguration {
        @Bean
        public WebMvcConfigurer corsConfigurer() {
                return new WebMvcConfigurerAdapter() {
                        @Override
                        public void addCorsMappings(CorsRegistry registry) {
                                registry.addMapping("/api/**");
                        }
                };
        }
}

这里我只是引用了一段Spring Boot 文档中的介绍,完整的介绍你可以查询Spring Framework 文档中关于 cors 的详细说明,为了方便查看,我把它放到下面直接显示:

27.1 Introduction
For security reasons, browsers prohibit AJAX calls to resources residing outside the current origin. For example, as you’re checking your bank account in one tab, you could have the evil.com website open in another tab. The scripts from evil.com should not be able to make AJAX requests to your bank API (e.g., withdrawing money from your account!) using your credentials.

Cross-origin resource sharing (CORS) is a W3C specification implemented by most browsers that allows you to specify in a flexible way what kind of cross domain requests are authorized, instead of using some less secured and less powerful hacks like IFRAME or JSONP.

As of Spring Framework 4.2, CORS is supported out of the box. CORS requests (including preflight ones with an OPTIONS method) are automatically dispatched to the various registered HandlerMappings. They handle CORS preflight requests and intercept CORS simple and actual requests thanks to a CorsProcessor implementation (DefaultCorsProcessor by default) in order to add the relevant CORS response headers (like Access-Control-Allow-Origin) based on the CORS configuration you have provided.

[Note]
Since CORS requests are automatically dispatched, you do not need to change the DispatcherServlet dispatchOptionsRequest init parameter value; using its default value (false) is the recommended approach.
27.2 Controller method CORS configuration
You can add an @CrossOrigin annotation to your @RequestMapping annotated handler method in order to enable CORS on it. By default @CrossOrigin allows all origins and the HTTP methods specified in the @RequestMapping annotation:

@RestController
@RequestMapping("/account")
public class AccountController {

    @CrossOrigin
    @RequestMapping("/{id}")
    public Account retrieve(@PathVariable Long id) {
        // ...
    }

    @RequestMapping(method = RequestMethod.DELETE, path = "/{id}")
    public void remove(@PathVariable Long id) {
        // ...
    }
}

It is also possible to enable CORS for the whole controller:

@CrossOrigin(origins = "http://domain2.com", maxAge = 3600)
@RestController
@RequestMapping("/account")
public class AccountController {

    @RequestMapping("/{id}")
    public Account retrieve(@PathVariable Long id) {
        // ...
    }

    @RequestMapping(method = RequestMethod.DELETE, path = "/{id}")
    public void remove(@PathVariable Long id) {
        // ...
    }
}

In the above example CORS support is enabled for both the retrieve() and the remove() handler methods, and you can also see how you can customize the CORS configuration using @CrossOrigin attributes.

You can even use both controller-level and method-level CORS configurations; Spring will then combine attributes from both annotations to create merged CORS configuration.

@CrossOrigin(maxAge = 3600)
@RestController
@RequestMapping("/account")
public class AccountController {

    @CrossOrigin("http://domain2.com")
    @RequestMapping("/{id}")
    public Account retrieve(@PathVariable Long id) {
        // ...
    }

    @RequestMapping(method = RequestMethod.DELETE, path = "/{id}")
    public void remove(@PathVariable Long id) {
        // ...
    }
}

27.3 Global CORS configuration
In addition to fine-grained, annotation-based configuration you’ll probably want to define some global CORS configuration as well. This is similar to using filters but can be declared within Spring MVC and combined with fine-grained @CrossOrigin configuration. By default all origins and GET, HEAD, and POST methods are allowed.

27.3.1 JavaConfig

Enabling CORS for the whole application is as simple as:

@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**");
    }
}

You can easily change any properties, as well as only apply this CORS configuration to a specific path pattern:

@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/api/**")
            .allowedOrigins("http://domain2.com")
            .allowedMethods("PUT", "DELETE")
            .allowedHeaders("header1", "header2", "header3")
            .exposedHeaders("header1", "header2")
            .allowCredentials(false).maxAge(3600);
    }
}

27.3.2 XML namespace

The following minimal XML configuration enables CORS for the /** path pattern with the same default properties as with the aforementioned JavaConfig examples:

<mvc:cors>
    <mvc:mapping path="/**"></mvc:mapping>
</mvc:cors>

It is also possible to declare several CORS mappings with customized properties:

<mvc:cors>

    <mvc:mapping path="/api/**"
        allowed-origins="http://domain1.com, http://domain2.com"
        allowed-methods="GET, PUT"
        allowed-headers="header1, header2, header3"
        exposed-headers="header1, header2" allow-credentials="false"
        max-age="123"></mvc:mapping>

    <mvc:mapping path="/resources/**"
        allowed-origins="http://domain1.com"></mvc:mapping>

</mvc:cors>

27.4 Advanced Customization
CorsConfiguration allows you to specify how the CORS requests should be processed: allowed origins, headers, methods, etc. It can be provided in various ways:

AbstractHandlerMapping#setCorsConfiguration() allows to specify a Map with several CorsConfiguration instances mapped to path patterns like /api/**.
Subclasses can provide their own CorsConfiguration by overriding the AbstractHandlerMapping#getCorsConfiguration(Object, HttpServletRequest) method.
Handlers can implement the CorsConfigurationSource interface (like ResourceHttpRequestHandler now does) in order to provide a CorsConfiguration instance for each request.
27.5 Filter based CORS support
In order to support CORS with filter-based security frameworks like Spring Security, or with other libraries that do not support natively CORS, Spring Framework also provides a CorsFilter. Instead of using @CrossOrigin or WebMvcConfigurer#addCorsMappings(CorsRegistry), you need to register a custom filter defined like bellow:

import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
import org.springframework.web.filter.CorsFilter;

public class MyCorsFilter extends CorsFilter {

    public MyCorsFilter() {
        super(configurationSource());
    }

    private static UrlBasedCorsConfigurationSource configurationSource() {
        CorsConfiguration config = new CorsConfiguration();
        config.setAllowCredentials(true);
        config.addAllowedOrigin("http://domain1.com");
        config.addAllowedHeader("*");
        config.addAllowedMethod("*");
        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        source.registerCorsConfiguration("/**", config);
        return source;
    }
}

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