【Java Web开发学习】跨域请求

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1、使用jsonp

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代码很简单不做解释
json和jsonp的区别阅读 https://kb.cnblogs.com/page/139725/

package ycx.crossdomain.controller;

import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Map;

@RestController
public class IndexController {

    @RequestMapping("/")
    public void index(HttpServletRequest request, HttpServletResponse response) throws Exception {

        Map<String, Object> dataMap = new HashMap<>();
        dataMap.put("status", 200);
        dataMap.put("message", "OK");
        dataMap.put("data", "hello world");

        ObjectMapper mapper = new ObjectMapper();
        String data = mapper.writeValueAsString(dataMap);

        PrintWriter out = response.getWriter();
        String callback = request.getParameter("callback");
        if (StringUtils.isEmpty(callback)) {
            out.print(data);
        } else {
            out.print(callback + "(" + data + ")");
        }
        out.flush();
        out.close();
    }
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>jsonp</title>
    <script type="text/javascript" src="js/jquery-3.4.1.js"></script>
</head>
<body>
<script>
    // has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
    // $.ajax({
    //     type: "GET",
    //     async: false,
    //     url: "http://localhost:9902",
    //     success: function (result) {
    //         console.dir(result);
    //     },
    //     error: function (e) {
    //         console.dir(e);
    //     }
    // });


    $.ajax({
        type: "GET",
        async: false,
        url: "http://localhost:9902",
        dataType: "jsonp",
        jsonp: "callback",
        jsonpCallback:"handler",
        success: function (result) {
            console.dir(result);
        },
        error: function (e) {
            console.dir(e);
        }
    });
</script>
</body>
</html>

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原文地址：https://www.cnblogs.com/yangchongxing/p/11454362.html