什么是跨域

　　使用JS获取数据时，涉及到的两个URL只要协议，域名，端口有任何一个不同，都当做是不同的域，相互访问就会有跨域问题；

怎样使用nginx解决跨域问题

　　步骤一：创建两个工程AProject,BProject

　　步骤二：在A工程中创建servlet

package com.wn;

import com.alibaba.fastjson.JSON;

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

@WebServlet("/aServlet")
public class AServlet extends HttpServlet {
    //resp.setContentType("text/html;charset=utf-8");
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }

    //方法四：使用nginx解決跨域問題
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        System.out.println("数据："+username);

        //响应
        resp.getWriter().write("success");
    }
}

　　步骤三：在B工程中创建jsp页面

<%--
  Created by IntelliJ IDEA.
  User: wn
  Date: 2020/2/6
  Time: 10:04
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>跨域</title>
    <script type="text/javascript" src="js/jquery-1.8.3.min.js"></script>
    <script>
        //使用nginx解决跨域问题
        $(function () {
            $("#button").click(function () {
                var username=$("#username").val();
                $.ajax({
                    url:"http://www.123.com:81/a/aServlet?username="+username,
                    type:"GET",
                    success:function (result) {
                        alert(result)
                    },
                    error:function () {
                        alert("error！！！")
                    }
                })
            })
        })

    </script>
</head>
<body>
　　<input type="text" name="username" id="username"/><button id="button" type="button">提交</button>
</body>
</html>

　　步骤四：配置nginx.conf文件

server {
        listen       81;
        server_name  www.123.com;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;

        location / {
            root   html;
            index  index.html index.htm;
        }
        
        #nginx解决跨域问题
        location /a {
            proxy_pass http://www.aproject.com:8080/;
            index index.html index.htm;
                    
        }
        location /b {
            proxy_pass http://www.bproject.com:8081/;
            index index.html index.htm;
        }
}