fetch异步简单版本（Tomcat 9）

smallRainFetch.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<title>fetch</title>
</head>
<body>

</body>
</html>

<input type="text" id="inputone" name="inputNameOne"
	value="fetchGet服务" />
<button onclick="getFromServer()">fetch和服务器交互</button>

<div id="smallRainShow" style="width: 400px; height: 300px;"></div>

<script type="text/javascript">
function getFromServer() {

	const valueTo = document.getElementById('inputone').value;
	fetch('<%=request.getContextPath()%>/smallRainFetchServlet?inputNameOne=' + valueTo)
		.then(smallRainRes => {
			return smallRainRes.text();
		})
		.then(smallRainData => {
			document.getElementById("smallRainShow").innerHTML = smallRainData;
		})
		.catch(error => {
			alert("error");
		});
}
  </script>

SmallRainFetchServlet.java java文件

package org.rain.servlet;

import java.io.IOException;
import java.io.PrintWriter;

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

@WebServlet("/smallRainFetchServlet")
public class SmallRainFetchServlet extends HttpServlet {
	@Override
	public void doPost(HttpServletRequest smallrainReq, HttpServletResponse smallRainRes) throws ServletException, IOException {
		doGet(smallrainReq, smallRainRes);
	}
	@Override
	public void doGet(HttpServletRequest smallrainReq, HttpServletResponse smallRainRes) throws ServletException, IOException {
		smallRainRes.setCharacterEncoding("UTF-8");
		PrintWriter smallrainOut = smallRainRes.getWriter();
		String smallRainWeb=smallrainReq.getParameter("inputNameOne");
		smallrainOut.print("得到服务器返回："+smallRainWeb);
	}
}