AJAX POST、PUT 和 DELETE 工作正常，但 GET 被 CORS 阻止

Question

I'm working with Java + Spring + PHPmyadmin and pure HTML + JS on my first API and trying to understand how ajax works and the problem is that I succeded doing a POST, PUT and DELETE but when I'm trying to do a GET通过 id ajax （类似于 DELETE one）chrome 正在返回 CORS 错误

Access to XMLHttpRequest at ' http://localhost:8081/dices/players/id ?{%22id%22:%22408%22}' from origin ' http://localhost ' has been blocked by CORS policy: Response to preflight请求未通过访问控制检查：请求的资源上不存在“Access-Control-Allow-Origin”header”。

我不明白为什么我只有在尝试 GET 时才会得到这个，而其他操作都可以正常工作...... API 的完整“后部”工作正常，并且已经过 POSTMAN 测试。 这是我在 Java 中的 CORS 过滤器（我不知道它是如何工作的 100%）：

@Component
public class SimpleCORSFilter implements Filter {
    private final Logger log = LoggerFactory.getLogger(SimpleCORSFilter.class);
    public SimpleCORSFilter() {
        log.info("SimpleCORSFilter init");
    }
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        response.setHeader("Access-Control-Allow-Origin", request.getHeader("Origin"));
        response.setHeader("Access-Control-Allow-Credentials", "true");
        response.setHeader("Access-Control-Allow-Methods", "POST, PUT, GET, OPTIONS, DELETE");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Headers", "Origin, Content-Type, Accept, X-HTTP-Method-Override, X-Requested-With, remember-me");
        chain.doFilter(req, res);
    }
    @Override
    public void init(FilterConfig filterConfig) {
    }
}

这是我在 JS 中的 function （几乎与 DELETE by id 相同，工作正常）

//GET PLAYER BY ID

function getById() {

    let playerID = document.getElementById("playerID").value;

        let playerToShow = {
            id: playerID,
        }

        let shownPlayer = JSON.stringify(playerToShow);

        $.ajax({
            type: "GET",
            url: "http://localhost:8081/dices/players/id",
            contentType: "application/json",
            data: shownPlayer, 
            success: function (data) {

                document.getElementById("data").innerHTML = JSON.stringify(data);
                console.log(data);
            },
            error: function () {

                alert("Something went wrong!);
            }
        });
    } 
}

我对所有这些 CORS 事情感到非常迷茫，所以我会感谢大家提供的任何线索！ 谢谢和对不起我的英语！

Answer 1

我想我明白了。 您需要将查询字符串参数而不是 JSON 数据传入 GET。

let shownPlayer = $.param(playerToShow);

字符串化 - "{\"id\":\"1234\"}"

参数-“id=1234”

Answer 2

尝试将其添加到您的 doFilter 方法中，就在 chain.doFilter 行之前

if (request.getMethod().equals("OPTIONS")) {
    resp.setStatus(HttpServletResponse.SC_OK);
    return;
}