流程图示

第一步：安装axios （前端）

第二步：创建utils/request.js文件

由于axios会自动转换JSON数据，那么前台post请求传给后台的数据就是json字符串，但是后台的getParameter..方法是根据key找value的，所以后台要求数据必须是键值对的方式，配置该文件可以实现前台传给后台的数据是键值对的方式

import axios from 'axios'
import qs from 'qs'
/**
 * axios的传参方式：
 * 1.url 传参 一般用于Get和Delete 实现方式：config.params={JSON}
 * 2.body传参 实现方式：config.data = {JSON}，且请求头为：headers: { 'Content-Type': 'application/json;charset=UTF-8' }
 * 3.表单传参 实现方式：config.data = qs.stringify({JSON})，且请求头为：且请求头为：headers: { 'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8' }
 */
// axios实例
const $http = axios.create({
	baseURL: 'http://localhost:8080/',
	timeout: 60000,
	headers: { 'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8' }
})
// 请求拦截器
$http.interceptors.request.use(
	(config) => {
		// 追加时间戳，防止GET请求缓存
		if (config.method?.toUpperCase() === 'GET') {
			config.params = { ...config.params, t: new Date().getTime() }
		}
		if (Object.values(config.headers).includes('application/x-www-form-urlencoded')) {
			config.data = qs.stringify(config.data)
		}
		return config
	},
	error => {
		return Promise.reject(error)
	}
)
// 响应拦截器
$http.interceptors.response.use(
	response => {
		const res = response.data
		return res
	},
	error => {
		return Promise.reject(error)
	}
)
// cros 跨域是否允许凭证
$http.defaults.withCredentials = true;
// 导出 axios 实例
export default $http

第三步：在main.js文件中配置axios

下载了axios必须得导入引用才可以使用,注意一点：必须全部写在挂载函数mount()之前
这里$http为reque.js中暴露出来的

第四步：配置跨域解决方案filter （后端）

对所有的网址进行拦截，设置好跨域请求后再释放

@WebFilter(filterName = "AllFilter",urlPatterns = "/*")
public class AllFilter implements Filter {
    public void destroy() {
    }
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
        HttpServletResponse response = (HttpServletResponse) resp;
        HttpServletRequest request = (HttpServletRequest) req;
//        response.setHeader("Access-Control-Allow-Origin", "*"); //允许所有的域名访问
        // 允许携带cookie
        response.setHeader("Access-Control-Allow-Origin",request.getHeader("origin"));
        response.setHeader("Access-Control-Allow-Methods", "POST, GET, PUT, PATCH, DELETE"); //允许的提交方式
        response.setHeader("Access-Control-Max-Age", "3600"); //最大有效时间
        response.setHeader("Access-Control-Allow-Headers", "x-requested-with, Content-Type, Accept, Origin"); //允许那些请求头
        response.setHeader("Access-Control-Allow-Credentials", "true"); //是否支持ajax提交cookie
        chain.doFilter(req, resp);
    }
    public void init(FilterConfig config) throws ServletException {
    }
}

第五步：在页面传数据发请求 （前端）

如果是get请求那么请求参数是通过url传递的 也就是

this.$axios.get("https://localhost:8080/login?user="+this.user+"&&password="+this.password).then(...)

如果是post请求那么请求参数通过对象的方式传递

第六步：编写Servlet （后端）

匹配请求的网址，对请求作出相应的操作，需要用到请求码和消息所以会封装几个类，实现响应给前台数据的一致，便于前台拿数据
Servlet:
使用JSON对象必须添加fastjson的jar包到lib目录下

@WebServlet(name = "LoginServlet2",urlPatterns = "/login")
public class LoginServlet2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        // 注意 ： 这里跟之前的不一样，需要改成json格式
        response.setContentType("application/json;charset=UTF-8");
        String user = request.getParameter("user");
        String password = request.getParameter("password");
        LoginService loginService = new LoginServiceImpl();
        User user1 =  loginService.logintoUser(user, password);
        PrintWriter writer = response.getWriter();
        String json="";
        if (user1!=null){
            //登录成功
            ResponseData<User> responseData = ResponseDataUtil.buildOk(user1);
            json = JSON.toJSONString(responseData);
        }else{
            json = JSON.toJSONString(ResponseDataUtil.buildOk(ResultEnums.LOGIN_FAIL));
        }
        writer.print(json);
        // 刷新，用于大文件
        writer.flush();
    }
}

请求码的属性类

public class Meta {
    private int status;
    private String msg;
    public int getStatus() {
        return status;
    }
    public void setStatus(int status) {
        this.status = status;
    }
    public String getMsg() {
        return msg;
    }
    public void setMsg(String msg) {
        this.msg = msg;
    }
}

各种请求码及信息的枚举类

public enum ResultEnums {
    OK(200, "请求成功"),
    CREATED(201, "创建成功"),
    DELETED(204, "删除成功"),
    UPDATED(205, "修改成功"),
    BAD_REQUEST(400, "请求的地址不存在或者包含不支持的参数"),
    UNAUTHORIZED(401,"未授权"),
    FORBIDDEN(403,"被禁止访问"),
    LOGIN_FAIL(414,"用户名或者密码错误"),
    NOT_FOUND(404,"请求的资源不存在"),
    UNPROCESABLE_ENTITY(422,"[POST/PUT/PATCH] 当创建一个对象时，发生一个验证错误"),
    INTERNAL_SERVER_ERROR(500,"内部错误");
    private int status;
    private String msg;
    ResultEnums(int status, String msg) {
        this.status = status;
        this.msg = msg;
    }
    public int getStatus() {
        return status;
    }
    public void setStatus(int status) {
        this.status = status;
    }
    public String getMsg() {
        return msg;
    }
    public void setMsg(String msg) {
        this.msg = msg;
    }
}

响应数据类

package com.ww.web.VuePag;
import java.io.Serializable;
/**
 * <p>Title: ${file_name}</p>
 * <p>Description: </p>
 * <p>Copyright: Copyright (c) 2020</p>
 * <p>Company: www.baidudu.com</p>
 *
 * @author suke
 * @version 1.0
 * @date ${date}
 */
public class ResponseData<T> implements Serializable {
    private Meta meta = new Meta();
    private T data;
    public ResponseData(int status, String msg, T data) {
        this.meta.setStatus(status);
        this.meta.setMsg(msg);
        this.data = data;
    }
    public ResponseData(int status, String msg) {
        this.meta.setStatus(status);
        this.meta.setMsg(msg);
    }
    public ResponseData(ResultEnums resultEnums) {
        this.meta.setStatus(resultEnums.getStatus());
        this.meta.setMsg(resultEnums.getMsg());
    }
    public ResponseData(ResultEnums resultEnums, T data) {
        this.meta.setStatus(resultEnums.getStatus());
        this.meta.setMsg(resultEnums.getMsg());
        this.data = data;
    }
    public ResponseData() {
    }
    public Meta getMeta() {
        return this.meta;
    }
    public void setMeta(Meta meta) {
        this.meta = meta;
    }
    public T getData() {
        return data;
    }
    public void setData(T data) {
        this.data = data;
    }
}

创建响应数据的工具类

/**
 * 带实体的统一返回
 * data 实体
 * <T>  实体类型
 *
 */
public class ResponseDataUtil {
    public static ResponseData buildOk(String msg) {
        return new ResponseData(ResultEnums.OK.getStatus(), msg);
    }
    public static <T> ResponseData buildOk(T data) {
        return new ResponseData<T>(ResultEnums.OK, data);
    }
    public static <T> ResponseData<T> buildOk(String msg,T data) {
        return new ResponseData(ResultEnums.OK.getStatus(), msg,data);
    }
    public static ResponseData buildOk(int status , String msg) {
        return new ResponseData(status, msg);
    }
    public static <T> ResponseData buildOk(int status, String msg, T data) {
        return new ResponseData<T>(status, msg, data);
    }
    public static ResponseData buildOk(ResultEnums resultEnums) {
        return new ResponseData(resultEnums);
    }
    public static <T> ResponseData buildCreate(T data) {
        return new ResponseData<T>(ResultEnums.CREATED, data);
    }
    public static <T> ResponseData buildDelete(T data) {
        return new ResponseData<T>(ResultEnums.DELETED, data);
    }
    public static <T> ResponseData buildUpdate(T data) {
        return new ResponseData<T>(ResultEnums.UPDATED, data);
    }
}

第七步：完善第五步中的请求

对响应回来的数据作出后续操作

login() {
			var that = this;  // 因为then中的是箭头函数，箭头函数this指向window，所以需要在开始时获取并赋值
			this.$axios.post('login', {
				user: that.user,
				password: that.password
			})
				.then(function (response) {
					// 处理成功情况
					console.log(response);
					if (response.meta.status === 200) {
						// 登录成功
						// 将接收回来的对象存放到本地存储中
						let admin = response.data;
						localStorage.setItem("token", admin.username)
						// 跳转页面
						that.$router.push({
							name: "index",
							// 将参数带入index页面
							query: {
								username: admin.username
							}
						})
					} else {
						// 登录失败
						alert(response.meta.msg);
					}
				})
				.catch(function (error) {
					// 处理错误情况  500
					alert("服务器出错")
				});
		}

使用注解使password反序列化