CORS策略已阻止从来源“ http：// localhost：3000”访问“ http：// localhost：9900 / jaxrs-post-example / rest / customers”的访存

如何解决CORS策略已阻止从来源“ http：// localhost：3000”访问“ http：// localhost：9900 / jaxrs-post-example / rest / customers”的访存

我从https://www.logicbig.com/tutorials/java-ee-tutorial/jax-rs/post-example.html下载了Jersey Java Rest Api示例

当我使用“在服务器上运行”运行该项目时，它接受了来自Postman的以下Rest api命令，并且运行正常：

GET http://localhost:9900/jaxrs-post-example/rest/customers

POST http://localhost:9900/jaxrs-post-example/rest/customers
{
  "firstName":"David","lastName":"Parker","school":"CSI","standard":"4","rollNumber":85
}

当我从ReactJS发送相同的命令时，服务器在ReactJS中显示以下错误。

CORS策略阻止从来源“ http：// localhost：3000”访问“ http：// localhost：9900 / jaxrs-post-example / rest / customers”处的访存：对预检请求的响应没有•通过访问控制检查：所请求的资源上不存在“ Access-Control-Allow-Origin”标头。如果不透明的响应可以满足您的需求，请将请求的模式设置为“ no-cors”，以在禁用CORS的情况下获取资源。

要解决此问题，我在RestServer.java中添加了以下内容 （基于How to handle CORS using JAX-RS with Jersey）

@Provider
@PreMatching
public class CorsFilter implements ContainerRequestFilter,ContainerResponseFilter {

    /**
     * Method for ContainerRequestFilter.
     */
    @Override
    public void filter(ContainerRequestContext request) throws IOException {

        // If it's a preflight request,we abort the request with
        // a 200 status,and the CORS headers are added in the
        // response filter method below.
        if (isPreflightRequest(request)) {
            request.abortWith(Response.ok().build());
            return;
        }
    }

    /**
     * A preflight request is an OPTIONS request
     * with an Origin header.
     */
    private boolean isPreflightRequest(ContainerRequestContext request) {
        return request.getHeaderString("Origin") != null
                && request.getmethod().equalsIgnoreCase("OPTIONS");
    }

    /**
     * Method for ContainerResponseFilter.
     */
    @Override
    public void filter(ContainerRequestContext request,ContainerResponseContext response)
            throws IOException {

        // if there is no Origin header,then it is not a
        // cross origin request. We don't do anything.
        if (request.getHeaderString("Origin") == null) {
            return;
        }

        // If it is a preflight request,then we add all
        // the CORS headers here.
        if (isPreflightRequest(request)) {
            response.getHeaders().add("Access-Control-Allow-Credentials","true");
            response.getHeaders().add("Access-Control-Allow-Methods","GET,POST,PUT,DELETE,OPTIONS,HEAD");
            response.getHeaders().add("Access-Control-Allow-Headers",// Whatever other non-standard/safe headers (see list above) 
                // you want the client to be able to send to the server,// put it in this list. And remove the ones you don't want.
                "X-Requested-With,Authorization," +
                "Accept-Version,Content-MD5,CSRF-Token,Content-Type");
        }

        // Cross origin requests can be either simple requests
        // or preflight request. We need to add this header
        // to both type of requests. Only preflight requests
        // need the prevIoUsly added headers.
        response.getHeaders().add("Access-Control-Allow-Origin","*");
    }
}

此外，我在web.xml中添加了以下内容

    <web-app>
  <display-name>JAX-RS Web Application</display-name>
  <servlet>
    <servlet-name>jersey-json-example-serlvet</servlet-name>
    <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
    <init-param>
        <param-name>com.sun.jersey.spi.container.ContainerResponseFilters</param-name>
        <param-value>com.javacodegeeks.rest.jersey.server.CORSFilter</param-value>
    </init-param>
    <init-param>
        <param-name>com.sun.jersey.config.property.packages</param-name>
        <param-value>com.javacodegeeks.rest.jersey.server</param-value>
    </init-param>
    <init-param>
        <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
        <param-value>true</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>jersey-json-example-serlvet</servlet-name>
    <url-pattern>/rest/*</url-pattern>
  </servlet-mapping>
</web-app>

当我尝试使用带有CORS的Flask + Python时，ReactJS的命令运行正常。

ReactJS更改： fetch（'http：// localhost：5000 / jaxrs-post-example / rest / customers'，

Flask + Python代码：

app = Flask(__name__)
app.config['SECRET_KEY'] = 'xyz'
app.config['CORS_HEADERS'] = 'Content-Type'
#Allow specific origin
cors = CORS(app,resources={r"/jaxrs-post-example/*": {"origins": ["http://localhost:3000"]}})

@app.route('/jaxrs-post-example/rest/customers',methods=['GET','POST'])
def getStudent():
    print("You are getting getStudent request")
    content = request.json
    id = content['id']
    name = content['name']
    address = content['address']
    phoneNumber = content['phoneNumber']
    print("id = ",id)
    print("name = ",name)
    print("address = ",address)
    print("phoneNumber = ",phoneNumber)
    json_object = JFY({"result": "getStudent is called"})
    print("json_results = ",json_object)
    print("response for getStudent = ",json_object.get_json())
    return json_object

输出完美

127.0.0.1 - - [08/Sep/2020 21:00:40] "OPTIONS /jaxrs-post-example/rest/customers HTTP/1.1" 200 -
127.0.0.1 - - [08/Sep/2020 21:00:41] "POST /jaxrs-post-example/rest/customers HTTP/1.1" 200 -
You are getting getStudent request
id =  2152
name =  David
address =  12,new street
phoneNumber =  8765489011
json_results =  <Response 39 bytes [200 OK]>
response for getStudent =  {'result': 'getStudent is called'}

---

问题：

1. 如何在Jersey Java中实现CORS（类似于Flask + Python）？
2. 请提供此问题的解决方案

解决方法

找到解决方法

根据视频： 在JAX-RS项目中启用CORS https://www.youtube.com/watch?v=CDEeOWKza2Q

步骤是：

右键单击任何软件包>新建>过滤器

    Java package > com.logicbig.example

    Class Name > CorsFilter > Next

    Double click /CorsFilter > Pattern > /rest/* > Ok > Next

    Ensure > Interface = javax.servlet.Filter > Finish

观察新类（CorsFilter）已创建

删除构造函数

在doFilter下添加以下内容

---

public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain) throws IOException,ServletException {
        HttpServletResponse resp = (HttpServletResponse) response;
        resp.addHeader("Access-Control-Allow-Origin","http://localhost:3000");
        resp.addHeader("Access-Control-Allow-Headers","*");
        resp.addHeader("Access-Control-Allow-Methods","*");
        chain.doFilter(request,response);
    }

---

构建路径>外部jar>添加> C：//Tomcat/lib/servlet-api.jar

观察：所有错误均已删除

重新启动Tomcat

在服务器上运行

观察：ReactJS中的CORS错误已删除

,

您必须从尝试访问的服务启用跨源资源共享。请检查相关链接here。这很好地解释了如何在使用Jersey的JAXRS中实现它。