使用react-router4.0实现重定向和404功能的方法

import React, { Component } from 'react';import axios from 'axios';import { Redirect } from 'react-router-dom';class Login extends Component{ constructor(){  super();  this.state = {value: '', logined: false};  this.handleChange = this.handleChange.bind(this);  this.toLogin = this.toLogin.bind(this); } handleChange(event) {  this.setState({value: event.target.value}) } toLogin(accesstoken) {  axios.post('yoururl',{accesstoken})   .then((res) => {    this.setState({logined: true});   }) } render() {  if(this.props.logined) {   return (    <Redirect to="/user"/>   )  }  return (   <div>     <input type="text" value={this.state.value} onChange={this.handleChange} />     <a onClick={() => { this.toLogin(this.state.value) }}>登录</a>   </div>  ) }}export default Login;

const LOGIN_SUCCESS = 'LOGIN_SUCCESS';const LOGIN_FAILED = 'LOGIN_FAILED';const LOGINOUT = 'LOGINOUT';const Login = function(state, action) { if(!state) {  console.log('state');  if(sessionStorage.getItem('usermsg')) {   return {    logined: true,    usermsg: JSON.parse(sessionStorage.getItem('usermsg'))   }  }  return {   logined: false,   usermsg: {}  } } switch(action.type) {  case LOGIN_SUCCESS:   return {logined: true,usermsg: action.usermsg};  case LOGIN_FAILED:   return {logined: false,usermsg:{}};  case LOGINOUT:   return {logined: false, usermsg: {}};  default:   return state }};export default Login;

<Switch> <Route path="/" exact component={Home}/> <Route path="/user" component={User}/> <Route component={NoMatch}/></Switch>