java循環沒有打印輸入流數據第一次迭代後

Question

我有一個Java程序，連接到一個在線資源，讀取數據，然後解析一個特定的信息（這是查看某個頁面的活躍reddit帳戶的數量） 。

我想自動執行此過程以給定的時間間隔重複它（爲了查看它是否工作，我將間隔設置爲5秒）。程序然後將這個數字打印到一個文件中，每次都在不同的行上。我知道主循環是迭代的，因爲我的output.txt文件有幾行，但它只能在第一次迭代中找到並打印數字。

package redditreader3; 

import java.io.*; 
import java.net.Socket; 
import java.util.Scanner; 
import java.util.regex.Matcher; 
import java.util.regex.Pattern; 

public class RedditReader3 { 
public static void main(String[] args) throws IOException, InterruptedException 
{ 
int i = 1; 
String host = args[0]; // www.reddit.com 

String resource = args[1]; // /r/toronto/about.json  

final int HTTP_PORT = 80; 
String command = "GET " + resource + " HTTP/1.1\n" + "Host:" + host 
    + "\n\n"; 

    /* This command requests reddit for the source code of the resource in args[1] at its host, args[0] to be printed through HTTP. */ 

Socket socket = new Socket(host, HTTP_PORT); 

    InputStream instream = socket.getInputStream(); 

     Scanner in = new Scanner(instream); 

    OutputStream outstream = socket.getOutputStream(); 

     PrintWriter out = new PrintWriter(outstream); 

File file = new File("output.txt"); 

    FileOutputStream F_outstream = new FileOutputStream(file); 

     PrintStream F_printstream = new PrintStream(F_outstream); 

/* Now that the connection has been established and all of the objects 
    are connected to each other, the command may be sent and the data 
    transfer may begin. */ 

String ActiveAccountsData = ("\"accounts_active\": (\\d+)"); 

String ActiveAccountsDataFOUND; 

Pattern ActiveAccountsPattern = Pattern.compile(ActiveAccountsData); 

Matcher ActiveAccountsMatcher; 

String input; 

while(i <= 4) 
{ 

    out.print(command); 
    out.flush(); 

    while(in.hasNextLine()) 
    { 
     input = in.nextLine(); 
     ActiveAccountsMatcher = ActiveAccountsPattern.matcher(input); 

     if(ActiveAccountsMatcher.find()) 
     { 
      ActiveAccountsDataFOUND = ActiveAccountsMatcher.group(1); 
      F_printstream.println(ActiveAccountsDataFOUND); 
      break; 
     } 
    } 
    i++; 
    F_printstream.println(); 
    Thread.sleep(5000); 
} 
} 
} 

我想也許in.hasNextLine()值被卡住的地方和需要更新，但我不能找到將它返回到該網站輸入的開頭方法。

Answer 1

您的掃描儀正在按預期工作。它正在通過流並打印內容。 你想要做的是倒回流。您可以使用Inputstream上的重置來完成此操作（有關詳細信息，請參閱javadoc）。您可能需要創建一個新的掃描器

Answer 2

您需要將您的循環圍繞整個方法。對於每次迭代，您需要重新建立連接並解析流。

請注意，你最好使用HttpURLConnection而不是直接套接字調用（這樣你就不必親自處理http頭，等等）。

Answer 3

您應該每5秒發出一個新的HTTP GET請求以獲取更新的數據。即在循環內移動您的InputStream/Scanner代碼。

此外，您可能需要使用HttpClient而不是原始套接字。

Answer 4

從當前位置的代碼刪除下面的線條和

Socket socket = new Socket(host, HTTP_PORT); 

InputStream instream = socket.getInputStream(); 

    Scanner in = new Scanner(instream); 

OutputStream outstream = socket.getOutputStream(); 

    PrintWriter out = new PrintWriter(outstream); 

更改爲以下，但不要忘了關閉資源（inputstreams和輸出流）：

while(i <= 4) 
{ 
    Socket socket = new Socket(host, HTTP_PORT); 



InputStream instream = socket.getInputStream(); 

    Scanner in = new Scanner(instream); 

OutputStream outstream = socket.getOutputStream(); 

    PrintWriter out = new PrintWriter(outstream); 

out.print(command); 
out.flush(); 

while(in.hasNextLine()) 
{ 
    input = in.nextLine(); 
    ActiveAccountsMatcher = ActiveAccountsPattern.matcher(input); 

    if(ActiveAccountsMatcher.find()) 
    { 
     ActiveAccountsDataFOUND = ActiveAccountsMatcher.group(1); 
     F_printstream.println(ActiveAccountsDataFOUND); 
     break; 
    } 
} 
i++; 
F_printstream.println(); 
//close resources 
Thread.sleep(5000); 

}