浏览器js在访问服务器中的资源时，会出现同一页面或者不同域名(协议，IP，端口)不可访问
例如:file://d://test.html页面(file协议)中通过ajax访问服务器api.test.com的接口(http协议)，由于协议不同，此时会出现浏览器访问不了后台接口的问题
此时需要在服务器接口的请求头配置好，当浏览器访问时就会根据请求头判断是否可以访问
前端代码
<!DOCTYPE html>
<html>
<head><meta charset="UTF-8"><title>跨域请求示例</title>
</head>
<body><button onclick="sendRequest()">发送请求</button><div id="result"></div><script>function sendRequest() {var xhr = new XMLHttpRequest();xhr.open('GET', 'http://localhost:8888/user/queryById?id=1', true);xhr.onreadystatechange = function() {if (xhr.readyState == 4 && xhr.status == 200) {document.getElementById('result').innerText = xhr.responseText;}};xhr.send();}</script>
</body>
</html>调用后台接口时报错
补充跨域过滤
package com.example.demo.config;import org.springframework.stereotype.Component;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@Component
public class CorsFilter implements Filter {@Overridepublic void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {HttpServletResponse response = (HttpServletResponse) res;HttpServletRequest request = (HttpServletRequest) req;response.setHeader("Access-Control-Allow-Origin", "*");response.setHeader("Access-Control-Allow-Methods", "*");response.setHeader("Access-Control-Allow-Credentials", "true");response.setHeader("Access-Control-Allow-Headers", "Authorization,Origin,X-Requested-With,Content-type,Accept,Access-Token");response.setHeader("Access-Control-Max-Age", "3600");chain.doFilter(request, response);}
}
再次请求，可以正常得到结果
