Reactjs 中的简单条件路由

如何实现条件路由，即当且仅当某些条件满足时，应该进行路由.

如果我们不直接点击localhost:8080/welcome个网址，欢迎点击.欢迎页面只应在登录后显示.

如何做到这一点，有人能帮我吗？

应用程序.js

import React, { Component } from 'react';
import Header from './Header';

class App extends Component{
  render(){
   return(
     <div>
       <Header />
     </div>
   );
  }
}
export default App;

头球.js

import React, { Component } from 'react';
import {Link} from 'react-router-dom';
import Login from './Login';
import SignUp from './SignUp';

class Header extends Component{
render(){
  return(
    <div>
    <nav class="navbar navbar-default">
     <div class="container-fluid">
     <ul class="nav navbar-nav">
      <li><Link to={Login}>Login</Link></li>
      <li><Link to={Login}>SignUp</Link></li>
    </ul>
    </div>
    </nav>
   
    </div>
   );
 } 
}

export default Header;

所有路由.js

import React, { Component } from 'react';
import { Switch, Route } from 'react-router-dom';
import Login from './Login';
import SignUp from './SignUp';
import Welcome from './Welcome';

class AllRoutes extends Component{
 render(){
   return(
     <Switch> 
       <Route exact path="/login" component={Login} />
       <Route exact path="/signup" component={SignUp} />
       <Route exact path="/Welcome" component={Welcome} />
     </Switch>
   );
  }
 }
 export default AllRoutes;

欢迎js

import React, { Component } from 'react'; 

class Welcome extends Component{
render(){
 return(
  <div>
   <h2>Welcome to MainPage..</h2>
  </div>
  );
 }
}
export default Welcome;