java如何获取HttpServletRequest

在Java中，可以通过以下方式获取HttpServletRequest：

1. 在Servlet中，可以直接从doGet()或doPost()方法的参数中获取HttpServletRequest对象，代码如下：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 获取HttpServletRequest对象
    HttpServletRequest httpRequest = request;
}

2. 在JSP页面中，可以通过pageContext对象获取HttpServletRequest对象，代码如下：

<%
    // 获取HttpServletRequest对象
    HttpServletRequest httpRequest = (HttpServletRequest) pageContext.getRequest();
%>

3. 在普通Java类中，可以通过ThreadLocal来获取HttpServletRequest对象，代码如下：

public class RequestHolder {
    private static final ThreadLocal<HttpServletRequest> requestHolder = new ThreadLocal<>();

    public static void set(HttpServletRequest request) {
        requestHolder.set(request);
    }

    public static HttpServletRequest get() {
        return requestHolder.get();
    }

    public static void remove() {
        requestHolder.remove();
    }
}

在Servlet的doFilter()方法中，可以将HttpServletRequest对象存放到ThreadLocal中，然后在普通Java类中通过ThreadLocal获取HttpServletRequest对象，代码如下：

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    RequestHolder.set(httpRequest);
    chain.doFilter(request, response);
    RequestHolder.remove();
}