import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
public class UrlDemoServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws IOException {
        // 獲取到類似 "http://example.com:8080/app/path/to/servlet"
        StringBuffer url = request.getRequestURL();
 
        // 如果還想要問號后面的查詢串，比如 "?a=1&b=2"
        String queryString = request.getQueryString(); // 可能為 null
 
        String fullUrl = (queryString == null) 
            ? url.toString() 
            : url.append('?').append(queryString).toString();
 
        response.getWriter().write("Full URL: " + fullUrl);
    }
}

import javax.servlet.http.HttpServletRequest;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;
 
@Controller
public class UrlDemoController {
 
    @GetMapping("/demo")
    @ResponseBody
    public String demo(HttpServletRequest request) {
        StringBuffer url = request.getRequestURL();
        String qs  = request.getQueryString();
        return (qs == null) ? url.toString() : url.append('?').append(qs).toString();
    }
}

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
 
public class UrlLoggingFilter implements Filter {
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        StringBuffer url = request.getRequestURL();
        String qs  = request.getQueryString();
        String fullUrl = (qs == null) ? url.toString() : url.append('?').append(qs).toString();
        System.out.println("Incoming request URL: " + fullUrl);
        chain.doFilter(req, res);
    }
}

String proto = request.getHeader("X-Forwarded-Proto");
if (proto == null) proto = request.getScheme();
 
String host  = request.getHeader("X-Forwarded-Host");
if (host == null) host = request.getServerName();
 
String port  = request.getHeader("X-Forwarded-Port");
if (port == null) port = String.valueOf(request.getServerPort());
 
String fullUrl = proto + "://" + host + (port.isEmpty() ? "" : ":" + port)
               + request.getRequestURI()
               + (qs == null ? "" : "?" + qs);

HttpGet get = new HttpGet("https://api.example.com/data?x=1");
System.out.println(get.getURI());  // 輸出 URI 對象

Request req = new Request.Builder()
    .url("https://api.example.com/data?x=1")
    .build();
System.out.println(req.url());  // okio.HttpUrl 對象