希望與Servlet交互的Java控制台程序

Question

我基本上正在實現一個Java控制台程序，該程序將HTTP請求發送到Servlet。 此代碼運行，但沒有任何輸出。 我在這里有兩個問題-

在url.openConnection（）之后，我看到了httpConn對象中“ connected”字段的值，它說是false。 但是，如果我刪除此評論

    //int responsecode = httpConn.getResponseCode();   

返回狀態碼200（成功）。 這是什么意思？ 是否建立連接？ 當我進行telnet-本地主機8080時，它說“按任意鍵繼續”，當我這樣做時，它說“與主機的連接丟失”。此外，執行上述代碼后，控制台將顯示此信息。

null
null
Servlet Reached

我在下面得到了異常（整個程序在調試模式下運行之后）

java.net.ProtocolException: Cannot write output after reading input.

當我完成執行下一行代碼時（調試模式）

StringBuffer requestParams = new StringBuffer();

控制台不再顯示輸出。 到底是什么情況？

另一個問題-現在，我要在HTTP POST消息中將字符串作為參數發送，但是如何發送整個對象？ 我必須使用序列化嗎？ 任何幫助將不勝感激。

package tutorial;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.net.*;
import java.util.Iterator;

class HttpUtility{

    private static HttpURLConnection httpConn;

    public static HttpURLConnection sendPostRequest(String requestURL,
            ArrayList list) throws IOException {

        URL url = new URL(requestURL);
        httpConn = (HttpURLConnection) url.openConnection();

        //int responsecode = httpConn.getResponseCode();       
        //httpConn.setDoInput(true); // true indicates the server returns response

        StringBuffer requestParams = new StringBuffer();

        if (list != null && list.size() > 0) {

            httpConn.setDoOutput(true); // true indicates POST request
            // creates the list string, encode them using URLEncoder
            Iterator iter = list.iterator();
            int index=0;

            while (iter.hasNext()) {
                String lValue = (String) iter.next();
                requestParams.append(URLEncoder.encode("params"+ index++, "UTF-8"));
                requestParams.append("=").append(
                        URLEncoder.encode(lValue, "UTF-8"));
                requestParams.append("&");
            }

            System.out.println(requestParams.toString());
            String requestParam = requestParams.toString();

            DataOutputStream wr = new DataOutputStream(httpConn.getOutputStream());
            wr.writeBytes(requestParam);
            wr.flush();
            wr.close();

            /*
            OutputStream ops = httpConn.getOutputStream();
            OutputStreamWriter writer = new OutputStreamWriter(ops);           
            writer.write(requestParams.toString());
            writer.flush();
            */

            /*
            OutputStream os = httpConn.getOutputStream();
            os.write(requestParam.getBytes());
            os.flush();
            os.close();
            */
        }

        return httpConn;
    }

    public static void disconnect() {
        if (httpConn != null) {
            httpConn.disconnect();
        }
    }
}


class ConsoleHttpRequest {

    public static String requestURL;

    public static void main(String[] args) {    

        ArrayList list = new ArrayList();

        requestURL = "http://localhost:8080/ServletTutorial/ConsoleToServlet"; // No Exception but no connection
        //requestURL = "https://localhost:8080/ServletTutorial/ConsoleToServlet"; //javax.net.ssl.SSLHandshakeException: Remote host closed connection during handshake
        //requestURL = "http://localhost"; // java.net.ConnectException: Connection refused: connect
        //requestURL="https://10.167.7.178"; // java.net.ConnectException: Connection refused: connect
        //requestURL="http://www.google.com"; // No Exception but no connection as well     

        list.add("Welcome");
        list.add("to");
        list.add("the");
        list.add("World");
        list.add("of");
        list.add("Java");
        list.add("Programming");

        try {
            HttpUtility.sendPostRequest(requestURL, list);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        HttpUtility.disconnect();
    }
}

這是從控制台程序接收請求並在控制台中簡單打印的servlet。

package tutorial;

    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;

    /**
     * Servlet implementation class ConsoleToServlet
     */
    public class ConsoleToServlet extends HttpServlet {
        private static final long serialVersionUID = 1L;

        /**
         * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
         */
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

            String s=request.getParameter("params1");
            System.out.println(s);
            System.out.println("Servlet Reached");
        }

        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

            String s=request.getParameter("params1");
            System.out.println(s);
            doPost(request,response);
        }

    }

Answer 1

為什么在“ url.openConnection（...）”之后得到“假”值

使用debugtool和tcpdump **（sudo tcpdump -s 0 -A port 80）**檢查后，我發現調用openConnection時未發送http請求標頭，就在您開始閱讀inputstream后，來自客戶端的http請求將被發送。

關於ProtocolException

如果調用“ httpConn.getResponseCode（）”，則表示已將http響應標頭發送到客戶端，因此無法發送http請求（除非您使用http協議的“管道”功能，但服務器必須支持它）一邊也）

發送整個對象
試試吧 ：

    HttpURLConnection httpConn =(HttpURLConnection) url.openConnection();       
    httpConn.setDoOutput(true);
    ObjectOutputStream objOts=new ObjectOutputStream(httpConn.getOutputStream());
    objOts.writeObject(new Object());
    objOts.close();