我想将角度为4的数据发送到javaservlet（跨域）

Question

我想将角度为4的数据发送到Java Servlet，但由于未通过访问控制而无法发送。我想使用Java Servlet将数据插入db

这是我的代码前端：data.service.ts

 import { Injectable } from '@angular/core';
 import { Http, Response } from '@angular/http';
 import { Headers, RequestOptions, ResponseOptions } from '@angular/http';
 import { Observable } from 'rxjs';
 import 'rxjs/add/operator/map';
 import 'rxjs/add/operator/toPromise';

 @Injectable()
 export class DataService {

 result: any;
 private url = '//localhost:8080/my-java-web/';
 constructor(private _http: Http) { }


 addBookWithPromise(user: object): Promise<object> {
  const headers = new Headers({ 'Content-Type': 'application/json', 
  "Access-Control-Allow-Origin": "*",
  "Access-Control-Allow-Methods":" GET, POST, OPTIONS",
  "Access-Control-Allow-Headers": "Content-Type",
  "Access-Control-Allow-Credentials": "true"});
  const options = new ResponseOptions({ headers: headers });
  return this._http.post(this.url + 'loginsuccess', user, 
   options).toPromise()
  .then(this.extractData)
  .catch(this.handleErrorPromise);
  }

  private extractData(res: Response) {
  const body = res.json();
   return body.data || {};
   }
   private handleErrorObservable (error: Response | any) {
    console.error(error.message || error);
   return Observable.throw(error.message || error);
   }
   private handleErrorPromise (error: Response | any) {
   console.error(error.message || error);
   return Promise.reject(error.message || error);
   }

    }

backend: java servlet

public class LoginSuccess extends HttpServlet {

protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    response.addHeader("Access-Control-Allow-Origin","*");
    response.addHeader("Access-Control-Allow-Methods"," GET, POST, OPTIONS");
    response.addHeader("Access-Control-Allow-Headers","Content-Type");
    response.addHeader("Access-Control-Allow-Credentials", "true");
    PrintWriter out = response.getWriter();

    String username = request.getParameter("username");
    String password = request.getParameter("password");



    System.out.println("Success" +username);

Thank You Very Much

Answer 1

您需要阅读CORS协议。不久前，我写了一篇关于实现CORS的博客 文章。它基于使用
Spring框架（特别是Spring Boot），而不是直接使用Servlet API，但是它确实对CORS的工作方式有相当广泛的解释。

您的特定问题是您仅处理POST。CORS协议涉及Web浏览器向您的服务器发出OPTIONS请求。

正是此OPTIONS请求必须在响应中返回Access-Control-Allow-Origin和相关标头。

如果浏览器在响应中看到这些标头，则它将执行POST。

如果未在对OPTIONS请求的响应中看到那些标头，则将收到HTTP错误，并显示类似“所请求的资源上没有’Access-Control-Allow- Origin’标头”和POST请求的信息。将不会。