springboot filter获取不到post请求参数

Spring Boot中的Filter是一种拦截所有请求的方式，无论是GET请求还是POST请求都会被Filter拦截到。但是有时候会遇到Filter获取不到POST请求参数的情况，这时候需要检查一下请求头中的Content-Type是否是application/x-www-form-urlencoded。

如果Content-Type是application/x-www-form-urlencoded，则需要通过HttpServletRequest.getParameter()方法来获取请求参数。例如：

public class MyFilter implements Filter {

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
 
        // 获取请求参数
        String param1 = request.getParameter("param1");
        String param2 = request.getParameter("param2");
        ...
 
        // 继续处理请求
        chain.doFilter(request, response);
    }
 
}

如果Content-Type是application/json，则需要通过读取请求体来获取请求参数。例如：

public class MyFilter implements Filter {

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
 
        // 获取请求体
        BufferedReader reader = request.getReader();
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line);
        }
 
        // 解析JSON参数
        JSONObject json = JSONObject.parseObject(sb.toString());
        String param1 = json.getString("param1");
        String param2 = json.getString("param2");
        ...
 
        // 继续处理请求
        chain.doFilter(request, response);
    }
 
}

总之，要根据请求头中的Content-Type来确定获取POST请求参数的方法，否则会导致获取不到参数的情况。