javascript - 来自本地服务器上项目的 servlet 的 Angular Http.get 请求(json 数据正确返回，但不显示，可以与模拟 api 一起使用)

Question

控制台错误:

Error with getting users from service. Response with status: 404 Not Found for URL: http://localhost:8080/ChatApp/GetAllUsersServlet

当我在某处部署外部项目时，会出现同样的问题，所以使用 url: http://java.cyclone2.khleuven.be:38034/ChatApp/GetAllUsersServlet 你可以自己看到一个包含 json 的有效 url，但仍然出现 404 错误。

Angular 代码需要来自本地服务器上运行的 servlet 的 json:

export class UserService {
  // private usersUrl = 'api/users'; // mock api
  private usersUrl = 'http://localhost:8080/ChatApp/GetAllUsersServlet'; // external users from local server
  private headers = new Headers({'Content-Type': 'application/json'});

  constructor(private http: Http) { }
  getUsers(): Promise<User[]> {
    return this.http.get(this.usersUrl)
               .toPromise() // Http.get returns RxJS Observeable, converted to Promise here
               .then(response => response.json().data as User[]) // .data for mock inMemoryDataService
               .catch(this.handleError);
  }

Servlet 返回什么:

[{"fname":"TestFname","password":"test","gender":"Female","name":"TestName","id":1,"email":"test@test.com","age":21,"username":"Test","status":"offline"},{"fname":"Test4Fname","password":"test","gender":"Female","name":"Test4Name","id":4,"email":"test4@test.com","age":21,"username":"Test4","status":"offline"},{"fname":"Test3Fname","password":"test","gender":"Female","name":"Test3Name","id":3,"email":"test3@test.com","age":28,"username":"Test3","status":"offline"},{"fname":"Test2Fname","password":"test","gender":"Male","name":"Test2Name","id":2,"email":"test2@test.com","age":22,"username":"Test2","status":"offline"}]

模拟 api 中的这件事确实给出了正确的结果:

import { InMemoryDbService } from 'angular-in-memory-web-api';
export class InMemoryDataService implements InMemoryDbService {
  createDb() {
    let users = [{"fname":"TestFname","password":"test","gender":"Female",
      "name":"TestName","id":1,"email":"test@test.com","age":21,"username":"Test","status":"offline"},
      {"fname":"Test4Fname","password":"test","gender":"Female",
      "name":"Test4Name","id":4,"email":"test4@test.com","age":21,"username":"Test4","status":"offline"},{"fname":"Test3Fname","password":"test","gender":"Female","name":"Test3Name","id":3,"email":"test3@test.com","age":28,"username":"Test3","status":"offline"},
      {"fname":"Test2Fname","password":"test","gender":"Male",
      "name":"Test2Name","id":2,"email":"test2@test.com","age":22,"username":"Test2","status":"offline"}]
    return {users};
  }
}

任何帮助将不胜感激，因为我真的不知道为什么它不起作用。尝试了类似的东西，但只是更少的 json 数据，并且有效。 是的，servlet 的服务器正在本地运行。

getUsers() 被使用并显示，但由于它适用于模拟数据，所以这应该没问题？:

export class UsersComponent  {
    users: User[];
    selectedUser: User;

    constructor(
      private userService: UserService,
      private router: Router) { }

    gotoInfo(): void {
      this.router.navigate(['/info', this.selectedUser.username]);
    }
    onSelect(user: User): void {
      this.selectedUser = user;
    }
    getUsers(): void {
      this.userService.getUsers().then(users => this.users = users);
    }
    ngOnInit(): void {
      this.getUsers();
    }
 }

Servlet(启用cors):

protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { UserDB db = new UserDB();

JSONArray array = new JSONArray();
for (User users: db.getAll()) {
    try {
        array.put(users.getJSONObject());
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

// setting the response type to json
response.setContentType("application/json");
// setting the CORS request
response.setHeader("Access-Control-Allow-Origin", "*");

response.getWriter().write(array.toString());

Answer 1

以前使用 in-memory-web-api 会扰乱您的 http 请求，除非您删除类似以下内容 InMemoryWebApiModule.forRoot(InMemoryDataService)来自您的 NgModule，那么您的请求应该会顺利进行。

编辑:根据代码注释实现，您知道以下内容:

完成此操作后，我还可以指出您的获取请求中存在问题，因为就目前情况而言，您将无法在组件中获取任何数据。您的响应仅包含一个数组，而不是 data ，所以它应该是:

.then(response => response.json() as User[]) 

<罢工>