Java 如何从 HttpServletRequest (Tomcat 9.0) 获取查询参数？
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How to get query parameters from HttpServletRequest (Tomcat 9.0)?
提问by Katrikken
The server recieves requests from two clients - Raspberry Pi and Android app, both send requests using HttpURLConnection. I need to pass parameters with theese requests, e.g:
服务器接收来自两个客户端的请求 - Raspberry Pi 和 Android 应用程序，两者都使用 HttpURLConnection 发送请求。我需要通过这些请求传递参数，例如：
http://192.168.0.10:8080/MyProject/MyServer/rpi/checktask?rpi="rpi"
doing it as:
这样做：
String requestUrl = "http://192.168.0.10:8080/MyProject/MyServer/rpi";
String query = String.format("/checktask?rpi=%s",
URLEncoder.encode("rpi", "UTF-8"));
URL url = new URL(requestUrl + query);
conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setDoInput(true);
conn.setRequestProperty("Accept-Charset", "UTF-8");
conn.connect();
The Servlet has annotation:
Servlet 有注释：
@WebServlet(name = "MyServer", urlPatterns = { "/MyServer/rpi/*", "/MyServer/app/*"})
But when Servlet gets request as above following happens:
但是当 Servlet 收到上述请求时，会发生以下情况：
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String path = request.getRequestURI(); // /MyProject/MyServer/rpi/*
String query = request.getQueryString(); // null
String context = request.getContextPath(); // /MyProject
String servlet = request.getServletPath(); // /MyServer/rpi
String info = request.getPathInfo(); // /*
}
Although according to those answers: How to use @WebServlet to accept arguments (in a RESTFul way)?and How come request.getPathInfo() in service method returns null?
虽然根据这些答案： How to use @WebServlet to accept arguments (in a RESTFul way)? 而 如何在服务方法返回null来request.getPathInfo（）？
it should look like this:
它应该是这样的：
String path = request.getRequestURI(); // /MyProject/MyServer/rpi//checktask?rpi="rpi"
String query = request.getQueryString(); // rpi="rpi"
String context = request.getContextPath(); // /MyProject
String servlet = request.getServletPath(); // /MyServer/rpi
String info = request.getPathInfo(); // /checktask?rpi="rpi"
What am I doing wrong?
我究竟做错了什么？
回答by Rohit Gaikwad
Your URL string is
您的网址字符串是
http://192.168.0.10:8080/MyProject/MyServer/rpi/checktask?rpi="rpi"
The name of the parameter in the above String is "rpi".
上述字符串中的参数名称为“ rpi”。
The below code will give you the required value of the parameter "rpi".
以下代码将为您提供参数“rpi”所需的值。
String rpi = request.getParameter("rpi");
