[JAVA] The story that the request parameter from the iPhone application could not be obtained successfully with the Servlet

When I was creating an iPhone app myself, I didn't understand the difference between getAttribute () and getParameter (). I couldn't get the request from the app with the Servlet, so I'll leave it as a memo.

The event that occurred this time is like this.

Send a request from the iPhone app 　　　　↓ Received by Servlet (The Servlet is reached, but the parameters in the request cannot be obtained.)

Cause

I wasn't trying to get the value with request.getAttribute. It seems that you have to get it with getParameter. .. ~~ (Jsp was completely blind because it could be obtained with getAttribute) ~~ 2020.05.22 postscript ↑ I couldn't get it. It seems that I was addicted to it because setAttribute and getAttribute were messed up in the first place. .. I studied again on this site. → getAttribute () method.

The detailed contents were described on this site. [Difference between getAttribute () and getParameter ()](https://www.it-swarm.dev/ja/java/difference between getattribute () and getparameter () / 971401730 / "Difference between getAttribute () and getParameter () the difference")

Verification

I tried to verify with a sample program to deepen the understanding. This is a sample program that displays the character string entered in the textField of the iPhone on the console.

・ IPhone screen

　→　

result##

・ Console screen

After all it was not possible to get it with getAttribute

Source##

** ・ iPhone screen (input screen) **

ViewController

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var testField: UITextField!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }
    
    //Executed when the send button is pressed to Servlet
    @IBAction func goServlet(_ sender: Any) {
        self.performSegue(withIdentifier: "goResultView", sender: nil)
    }
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        
        print("prepare starts operation")
        //Set URL
        guard let req_url = URL(string: "http://localhost:8080/Test/TestServlet")
            else{return}
        print("url set complete")
        
        //Declare the information required for the request
        var req = URLRequest(url: req_url)
        print("Declaration of request")
        //Specify POST
        req.httpMethod = "POST"
        //Set POST data as BODY
        req.httpBody = "test=\(self.testField.text!)".data(using: .utf8)
        
        //Create session
        let session = URLSession(configuration: .default,delegate: nil, delegateQueue: OperationQueue.main)
        print("Create session")

                //Register request as a task
                let task = session.dataTask(with: req, completionHandler: {
                    (data, response ,error) in
        

                })
                //request send
                task.resume()
            }
   
}

** ・ iPhone screen (result screen) **

• Swift code is not defined on the result screen of iPhone

** ・ Java Servlet **

TestServlet

package servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class testServlet
 */
@WebServlet("/TestServlet")
public class TestServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public TestServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub

		request.setCharacterEncoding("UTF-8");
		response.setContentType("text/html; charset=UTF-8");

		System.out.println("Reaching the POST method of the Servlet");
		System.out.println("When received by getAttribute:" + "The character string sent from the iPhone app is" + request.getAttribute("test") + "is.");
		System.out.println("When received by getParameter:" + "The character string sent from the iPhone app is" + request.getParameter("test") + "is.");
	}

}