基本的Java Web服務器 - 接收SocketException：連接重置

Question

我試圖創建一個基本的HTTP/1.1兼容的Web服務器，它支持持久連接的簡單GET請求。我得到一個SocketException：在第61行發生連接重置錯誤（如果（行== == || line.equals（「」））。我測試它通過運行它，然後將我的瀏覽器指向本地主機portnumber。當我用一個帶有多個圖像的頁面測試它時，似乎只有一個請求正在異常發生前處理，但我不確定有什麼問題，因爲這是我第一次嘗試在任何類型的套接字編程中使用。除去DataOutputStream類後，我更新的代碼：

import java.io.BufferedReader; 
import java.io.ByteArrayOutputStream; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.InputStreamReader; 
import java.io.ObjectOutputStream; 
import java.io.PrintWriter; 
import java.net.ServerSocket; 
import java.net.Socket; 
import java.net.URI; 
import java.net.URISyntaxException; 
import java.text.SimpleDateFormat; 
import java.util.Date; 
import java.util.HashMap; 
import java.util.StringTokenizer; 

public class webserve 
{ 
    public static void main(String[] args) throws Exception 
    { 
     String rootPath = "~/Documents/MockWebServerDocument/"; 
     int port = 10000; 

     if(rootPath.startsWith("~" + File.separator)) 
     { 
      rootPath = System.getProperty("user.home") + rootPath.substring(1); 
     } 

     String requestLine=""; 
     StringTokenizer tokens=null; 
     String line, command; 
     Date date = new Date(); 
     String connectionStatus=""; 


     //Create new server socket listening on specified port number 
     ServerSocket serverSocket = new ServerSocket(port); 

     while(true) 
     { 
      //Wait for a client to connect and make a request 
      Socket connectionSocket = serverSocket.accept(); 
      System.out.println("Socket opened"); 

      //Input stream from client socket 
      BufferedReader incomingFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream())); 
      //PrintWriter to send header to client socket 
      PrintWriter outgoingHeader = new PrintWriter(connectionSocket.getOutputStream(),true); 
      //OutputStream to send file data to client socket 
      ObjectOutputStream outgoingFile = new ObjectOutputStream(connectionSocket.getOutputStream()); 
      //Date format for HTTP Header 
      SimpleDateFormat HTTPDateFormat = new SimpleDateFormat("EEE MMM d hh:mm:ss zzz yyyy"); 


      //Create a HashMap to store the request header information 
      HashMap<String,String> requestHeader = new HashMap<String,String>(); 

      while(connectionSocket.isConnected()) 
      { 
       //requestHeader.clear(); 

       while((line = incomingFromClient.readLine()) != null) 
       { 
        if(line.isEmpty()) 
        { 
         break; 
        } 
        //If this is the first line of the request, i.e doesnt contain a colon 
        if(!(line.contains(":"))) 
        { 
         requestLine = line; 
         requestHeader.put("Request", requestLine); 
        } 
        else 
        { 
         //Otherwise, find the colon in the line and create a key/value pair for the HashMap 
         int index = line.indexOf(':')+2; 
         String header = line.substring(0,index-1); 
         line = line.substring(index).trim(); 

         requestHeader.put(header, line); 

         System.out.println(header + " " + line); 
        } 
       } 

       connectionStatus = (String)requestHeader.get("Connection:"); 
       requestLine = (String)requestHeader.get("Request"); 

       System.out.println("RequestLine: " + requestLine); 

       if(!requestLine.equals("")||!(requestLine.equals(null))) 
       { 
        tokens = new StringTokenizer(requestLine); 

        command = tokens.nextToken(); 
        String filename = tokens.nextToken(); 
        filename = cleanUpFilename(filename); 
        String fullFilepath = rootPath + filename; 
        System.out.println("Full FilePath: " + fullFilepath); 

        File file = new File(fullFilepath); 

        //Get the number of bytes in the file 
        int numOfBytes=(int)file.length(); 

        //Open a file input stream using the full file pathname 
        FileInputStream inFile = new FileInputStream(fullFilepath); 

        //Create byte array to hold file contents 
        byte[] fileInBytes = new byte[numOfBytes]; 

        inFile.read(fileInBytes,0,numOfBytes); 

        inFile.close(); 


        //Write the header to the output stream 
        outgoingHeader.print("HTTP/1.1 200 OK\r\n"); 
        outgoingHeader.print("Date: " + HTTPDateFormat.format(date)+"\r\n"); 
        outgoingHeader.print("Server: BC-Server\r\n"); 
        outgoingHeader.print("Last-Modified: " + HTTPDateFormat.format(file.lastModified())+"\r\n"); 
        outgoingHeader.print("Connection: keep-alive\r\n"); 
        outgoingHeader.print("Content-Length: " + numOfBytes); 
        outgoingHeader.print("\r\n\r\n");    

        //When the header has been printed, write the byte array containing the file 
        //to the output stream 
        outgoingFile.writeObject(fileInBytes); 

        if(!(connectionStatus.equals("keep-alive"))) 
        { 
         System.out.println("Closing: " + connectionStatus); 
         outgoingHeader.close(); 
         outgoingFile.close(); 
         break; 
        } 
        else 
         continue; 

       }  

      } 

     } 
    } 

    public static String cleanUpFilename(String filename) 
    { 
     //If there is a "/" at the start of the filename, then remove it 
     if(filename.charAt(0) == '/') 
     { 
      filename = filename.substring(1); 
     } 

     //If we are given an absolute URI request, strip all characters 
     //before the third "/" 
     if(filename.startsWith("http://")); 
     { 
      try 
      { 
       URI httpAddress = new URI(filename); 

       //Get the path from the supplied absolute URI, that is remove 
       //all character before the third "/" 
       filename = httpAddress.getPath(); 

       //Again, we may have to trim this modified address if there is an 
       //extra "/" at the start of the filename 
       if(filename.charAt(0) == '/') 
       { 
        filename = filename.substring(1); 
       } 
      } 
      catch (URISyntaxException e) 
      {     
       e.printStackTrace(); 
      } 
     } 

     return filename; 
    } 

}

這裏是我的錯誤跟蹤：

Exception in thread "main" java.net.SocketException: Connection reset 
    at java.net.SocketInputStream.read(SocketInputStream.java:185) 
    at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:282) 
    at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:324) 
    at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:176) 
    at java.io.InputStreamReader.read(InputStreamReader.java:184) 
    at java.io.BufferedReader.fill(BufferedReader.java:153) 
    at java.io.BufferedReader.readLine(BufferedReader.java:316) 
    at java.io.BufferedReader.readLine(BufferedReader.java:379) 
    at webserve.main(webserve.java:61) 

任何幫助將不勝感激，因爲我在完全損失。

Answer 1

嘗試使用telnet，wget或curl而不是chrome來測試連接，因爲您可以控制雙方的TCP/IP連接。

我認爲您的網絡客戶端正在關閉它的連接，並且您嘗試再次從該套接字讀取（是的，即使isConnected()在遠程方關閉連接時也會引發此錯誤）。我也很抱歉地說，沒有簡單的方法來對付這個問題，而是抓住例外情況並優雅地處理它。

這是一個經常發生在同步套接字上的問題。嘗試使用java.nio通道和選擇器。

Answer 2

您不能使用DataOutputStream，它用於Java-Java通信。嘗試Writer用於編寫標題，以及用於編寫文件內容的原始OutputStream。

發生什麼事是瀏覽器看到無效的響應，並關閉連接。服務器仍在寫信給客戶端，客戶端響應RST，因爲連接已經結束。

Answer 3

同時使用多個輸出流是非常成問題的。在這種情況下，您不應創建ObjectOutputStream，直到您確定要寫入對象並且已經寫入並刷新標題爲止，因爲ObjectOutputStream會將寫入標頭寫入輸出中，在您的當前代碼中它將出現在任何標題之前，可能會導致客戶bar喝。

通常，SocketException: Connection Reset通常表示您已寫入已由對等方關閉的連接。在這種情況下，對等端是客戶端，而客戶端是Web瀏覽器，它可以表示任何東西，例如，用戶停止加載頁面，他瀏覽了一下，退出瀏覽器，關閉了標籤頁。這不是你的問題。只需關上插座並忘記它。

出於同樣的原因，你的服務器也應該設置一個合理的讀取超時時間，比如說10-30秒，並且如果它觸發，就進行保護。

Answer 4

你的服務器最明顯的問題是它不是多線程的。重新閱讀你對問題的描述後，這似乎是根本原因。每個連接需要一個線程。在serverSocket.accept()之後，創建一個新的線程來處理connectionSocket。

while(true) 
    { 
     //Wait for a client to connect and make a request 
     Socket connectionSocket = serverSocket.accept(); 

     new Thread() 
     { 
      public void run() 
      { 
       //Input stream from client socket 
       BufferedReader incomingFromClient = ... 

       etc 

      } 
     }.start();