HTML5 FormData在Java Servlet request.getParameter()中返回null

Map<String, String[]> parameterMap = request.getParameterMap();

for (String key : parameterMap.keySet()) {
    String[] values = parameterMap.get(key);
    if (values.length == 0) {
        // Do something with empty values, such as ignoring them.
    } else {
        // Process non-empty values.
    }
}

InputStream inputStream = request.getInputStream();

@WebServlet("/example")
public class ExampleServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Part[] parts = request.getParts();
        for (Part part : parts) {
            String name = part.getName();
            InputStream inputStream = part.getInputStream();
            // Process the input stream.
        }
    }
}