@CrossOrigin 跨域注解

在spring 4.2后，提供了跨域注解@CrossOrigin

https://spring.io/guides/gs/rest-service-cors/

Enabling CORS

Controller method CORS configuration

So that the RESTful web service will include CORS access control headers in its response, you just have to add a @CrossOrigin annotation to the handler method:

src/main/java/hello/GreetingController.java

用例：

 　@CrossOrigin(origins = "http://localhost:9000")
    @GetMapping("/greeting")
    public Greeting greeting(@RequestParam(required=false, defaultValue="World") String name) {
        System.out.println("==== in greeting ====");
        return new Greeting(counter.incrementAndGet(), String.format(template, name));
    }

This @CrossOrigin annotation enables cross-origin requests only for this specific method. By default, its allows all origins, all headers, the HTTP methods specified in the @RequestMapping annotation and a maxAge of 30 minutes is used. You can customize this behavior by specifying the value of one of the annotation attributes: origins, methods, allowedHeaders, exposedHeaders, allowCredentials or maxAge. In this example, we only allow http://localhost:9000 to send cross-origin requests.

@CrossOrigin注解是被注解的方法具备接受跨域请求的功能。默认情况下，它使方法具备接受所有域，所有请求消息头的请求。。。。这个例子中，我们仅接受

http://localhost:9000发送来的跨域请求。