如何發送請求並繼續回覆，併發送回客戶？

Question

客戶端通過HTTP請求（通過瀏覽器發送）調用Servlet，然後Servlet應該向外部網站發送請求（get），並從網站接收響應（post）。 Servlets繼續響應並向客戶端發送響應（post）。

我的問題是如何發送和接收Servlet中的請求/響應並將某些內容發送回客戶端？

Answer 1

您可以先創建URL，然後使用URLConnection對象連接和接收響應，下面的GET請求/響應

URL url = new URL(urlString); 
HttpURLConnection c = (HttpURLConnection)url.openConnection(); //connecting to url 
c.setRequestMethod("GET"); 
BufferedReader in = new BufferedReader(new InputStreamReader(c.getInputStream())); //stream to resource 
String str; 
while ((str = in.readLine()) != null) //reading data 
    responsestring += str+"\n";//process the response and save it in some string or so 
in.close(); //closing stream 
response.getWriter().write(responsestring); 

UPDATE 對於POST請求/響應這樣做

URL obj = new URL(url); 
HttpsURLConnection con = (HttpsURLConnection) obj.openConnection(); 

con.setRequestMethod("POST"); 

String urlParameters = ..; 

con.setDoOutput(true); 
DataOutputStream wr = new DataOutputStream(con.getOutputStream()); 
wr.writeBytes(urlParameters); 
wr.flush(); 
wr.close(); 

BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream())); 
String inputLine; 
StringBuffer res = new StringBuffer(); 

while ((inputLine = in.readLine()) != null) { 
    res.append(inputLine); 
} 
in.close(); 
//process response 
response.getWriter().write(res); 

Answer 2

您可以使用以下格式的請求的集合屬性：request.setAttribute(String key, Object value)。

例子：

public class FindPerson extends HttpServlet { 

    // ... doGet implementation 

    @Override 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 

     // data to send to the client 
     String name = "John White"; 
     int age = 54; 



     // Adding attributes to the request 
     request.setAttribute("personName", name); 
     request.setAttribute("personAge", age); 

     // Sending the result to the.jsp page 
     getServletContext().getRequestDispatcher("/WEB-INF/result.jsp").forward(request, response); 

     } 
    } 
} 

在此之後，您可以使用JSTL閱讀JSP頁面上這樣的數據：

<p>Name: ${ requestScope.personName } </p> 
<p>Age: ${ requestScope.personAge } </p> 

其中personName和personAge是鍵地圖。你使用request.setAttribute來設置它們。

!!!更新！

在你的情況下，你會調用其他的servlet，它將執行對外部站點的請求等。所有這些（從外部站點收集數據+處理這些數據）將被放置代替設置的代碼姓名和年齡的值（見上面的例子）。 希望它有幫助！

Answer 3

URL url = new URL(urlString); 
HttpURLConnection c = (HttpURLConnection)url.openConnection(); //connecting to url 
c.setRequestMethod("GET"); 
BufferedReader in = new BufferedReader(new InputStreamReader(c.getInputStream())); //stream to resource 
String str; 
while ((str = in.readLine()) != null) //reading data 
    responsestring += str+"\n";//process the response and save it in some string or so 
in.close(); //closing stream 
response.getWriter().write(responsestring);