react与后端交互（包括通过axios进行跨域访问）

package com.example.demo.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class HellowServlet2
 */
@WebServlet("/HellowServlet2")
public class HellowServlet2 extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public HellowServlet2() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        System.out.println("getParameter: " + request.getParameter("id"));
        System.out.println("getParameterMap: " + request.getParameterValues("books"));
        
        
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("Cache-Control", "no-cache");
        response.setCharacterEncoding("UTF-8");
        //response.setContentType("application/json");
        response.setContentType("application/x-www-form-urlencoded");
        
        response.getWriter().println("{\"name\":\"lance\",\"id\":\"44\"}"); //JSONUtil.parse(CommonResult.forbidden(e.getMessage()))
        response.getWriter().flush();
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

    axios.request({
            headers:{  //非必须
                "Content-Type":"application/x-www-form-urlencoded"
            },
            url:Url,
            params:Params//,    //参数类型二
            //withCredentials: true//跨域设置，不可用
        })
          .then(function (response) {
            let data =response.data
            console.log(data.name);

            ts.getData(data.name);
          })
        //   .then(aaa => this.setState({ //在axios中setState方法二
        //       argName:aaa.data.name
        //   }))
          .catch(function (error) {
            console.log(error);
          });
          
          
    getData(newName){
        this.setState({
            argName: newName
        });
    }

"proxy": "http://127.0.0.1:8084"

{
  "name": "react-test",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@testing-library/jest-dom": "^5.16.4",
    "@testing-library/react": "^13.1.1",
    "@testing-library/user-event": "^13.5.0",
    "axios": "^0.27.2",
    "react": "^18.1.0",
    "react-dom": "^18.1.0",
    "react-scripts": "5.0.1",
    "web-vitals": "^2.1.4"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },
  "homepage": ".", 
  "main": "index.html",
  "proxy": "http://127.0.0.1:8084"
}

// let  BaseURL="http://127.0.0.1:8084"
        let  BaseURL="/api" //默认proxy代理的接口
        let  Url="/HellowServlet2"



        // let Books = ['aaa','bbb'];

        let Params= {
            "id" : "3",
            "name": "ll",
            "age": "18"
        }

        //axios.defaults.headers["Content-Type"] = "application/x-www-form-urlencoded";

        //全局配置baseURL[URL三个字母必须大写，不然axios不认]

        let ts = this;//在axios中setState方法一

        axios.request({
            headers:{  //非必须
                "Content-Type":"application/x-www-form-urlencoded"//,
                // "Access-Control-Allow-Origin":"http://127.0.0.1", //不可用
                // "Access-Control-Allow-Credentials": "true"//不可用
            },
            // method: 'get', //非必须
            //baseURL:BaseURL,//使用proxy时，无需配置
            url:Url,
            // data:Qs.stringify(Params), //参数类型一
            params:Params//,    //参数类型二
            //withCredentials: true//跨域设置 //不可用
        })
          .then(function (response) {
            let data =response.data
            console.log(data.name);

            ts.getData(data.name);
          })
        //   .then(aaa => this.setState({ //在axios中setState方法二
        //       argName:aaa.data.name
        //   }))
          .catch(function (error) {
            console.log(error);
          });
    }

    getData(newName){
        this.setState({
            argName: newName
        });
    }