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java - BufferReader 卡在 readline() 中

转载 作者：行者123 更新时间：2023-12-02 01:50:30 24 4
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我正在制作一个 HTTP 服务器和 HTTP Web 客户端，用于简单的 Http 请求和响应。

这是服务器的代码

import java.io.*;
import java.net.*;
import java.util.*;

public final class WebServer{

public static void main(String[] args) throws Exception{
    //storing port number
    int port = 2048;

    //open socket and wait for TCP connection

    ServerSocket serverConnect = new ServerSocket(port);
    System.out.println("Server started.\nListening for connections on port : " + port + " ...\n");

        // we listen until user halts server execution
    while (true) {
        //Construct an object to process the HTTP request message. 
        //This will call another class where we do everything else
        HttpRequest request = new HttpRequest(serverConnect.accept());

        //create a new thread to process the request
        Thread thread = new Thread(request);
        thread.start();

    } //end of while

}//end of main
}//end of the class webServer

HttpRequest类的代码如下:

import java.io.*;
import java.net.*;
import java.util.*;

final class HttpRequest implements Runnable{

final static String CRLF = "\r\n";
Socket socket;  

//start of constructor
public HttpRequest(Socket socket) throws Exception{

    this.socket=socket;
}//end of constructor

//Implement the run() method of the Runnable interface.
public void run(){

    try{
        processRequest();
    }
    catch(Exception e){
        System.out.println(e);
    }
}//end of run

private void processRequest() throws Exception{

    //Get a reference to the scoket's input and output streams.
    InputStream is = socket.getInputStream();
    DataOutputStream os = new DataOutputStream(socket.getOutputStream());

    //set up the stream filters
    BufferedReader br = new BufferedReader(new InputStreamReader(is));
    //Get the request line of the HTTP request message.
    String requestLine = br.readLine();

    //Display the request line
    System.out.println();
    System.out.println(requestLine);

    //Get and display the header lines.

    String headerLine = null;
        while((headerLine = br.readLine()).length()!=0){
            System.out.println(headerLine);
        }
        //System.out.println(requestLine);

    //Extract the filename from the request line.
    StringTokenizer tokens = new StringTokenizer(requestLine);
    tokens.nextToken(); //skip over the method, which should be. "GET"
    String fileName = tokens.nextToken();

    //Prepend a "." so that file request is within the current directory
    fileName = "." + fileName;
    //printing for test
    //System.out.println(fileName);

    //Open the requested file
    FileInputStream fis = null;
    boolean fileExists = true;
    try{
        fis = new FileInputStream(fileName);
    }
    catch(FileNotFoundException e){
        fileExists = false;
    }

    //Construct the response message
    String statusLine = null;
    String contentTypeLine = null;
    String entityBody = null;

    if(fileExists){
        statusLine = tokens.nextToken();
        contentTypeLine = "Content-type: " + contentType(fileName) + CRLF;
    }
    else{
        statusLine = "HTTP/1.1 404 File Not Found";
        contentTypeLine =  "Content-type: " + "text/html" + CRLF;
        entityBody = "<html><head><title>Not Found </title></head>" +
                     "<BODY>Not Found</body></html>";
    }

    //send the status line
    os.writeBytes(statusLine);

    //send the content Type
    os.writeBytes(contentTypeLine);

    //send a blank line to indicate the end of the header lines
    os.writeBytes(CRLF);

    //send the entity Body

    if(fileExists){
        sendBytes(fis, os);
        fis.close();
    }
    else{
        os.writeBytes(entityBody);
        os.writeBytes(CRLF);

    }

    //Close scokets and streams.
    fis.close();
    os.close();
    br.close();
    socket.close();

}//end of processRequest

private static String contentType(String fileName){
    if(fileName.endsWith(".htm") || fileName.endsWith(".html")){
        return "text/html";
    }
    if(fileName.endsWith(".gif")){
        return "image/gif";
    }
    if(fileName.endsWith(".jpeg") || fileName.endsWith(".jpg")){
        return "image/jpeg";
    }
    return "application/octet-stream";
}// end of contentType

private static void sendBytes(FileInputStream fis, OutputStream os) throws Exception{
    //Construct a 1k buffer to hold bytes on their way to the Socket

    byte[] buffer = new byte[1024];
    int bytes = 0;

    //Copy requested file into the scoket's output stream.
    while((bytes = fis.read(buffer)) != -1){
        os.write(buffer, 0, bytes);
    }//end of while
}//end of sendBytes


} // end of the class

当我从 Chrome 网络浏览器发出请求时，代码工作正常。不过，我也制作了WebClient。当我从 WebClient 发出请求时，我被卡住了，因为程序永远运行。

据我跟踪，指针不会从服务器端的 while 循环中的 br.readline 移动。

我的客户的代码如下。

import java.io.*;
import java.net.*;
import java.util.*;

public class WebClient{

final static String CRLF = "\r\n";

public static void main(String [] args) {
  String serverName = args[0];
  int port = Integer.parseInt(args[1]);
  try {
     // System.out.println("Connecting to " + serverName + " on port " + port);
     Socket client = new Socket(serverName, port);

     System.out.println("Just connected to " + client.getRemoteSocketAddress());
     OutputStream outToServer = client.getOutputStream();
     DataOutputStream out = new DataOutputStream(outToServer);

     out.writeUTF("GET /" +args[2] +" HTTP/1.1");
     out.writeUTF(CRLF);
     out.writeUTF("Host: "+client.getLocalSocketAddress());
     out.writeUTF(CRLF);   
     out.writeUTF("Connection: close" + CRLF);
     out.writeUTF("User-agent: close" + CRLF);
     out.writeUTF(CRLF);  

    //Cache-Control: max-age=0


     System.out.println("Just connected to 1 ");      
     InputStream inFromServer = client.getInputStream();
              System.out.println("Just connected to 2 "); 
     BufferedReader br = new BufferedReader(new InputStreamReader(inFromServer));
              System.out.println("Just connected to 3 ");
     String headerLine = null;
     while((headerLine = br.readLine()).length()!=0){
            System.out.println("asd"+headerLine);
        }
      System.out.println("Just connected to 4 ");
     client.close();
      System.out.println("Just connected to 5 ");


  } catch (IOException e) {
     e.printStackTrace();
  }

}

}//end of the class WebClient

谁能帮我解决这个问题。

谢谢。

最佳答案

首先，您必须删除 HttpRequest 中的 fis.close(); 行(就在 os.close(); 之前) code> 类:如果不存在文件，此行会引发 NullPointerException，因为 fis 为空，因此在向浏览器发送 Not Found 响应后，您的服务器不会关闭从该浏览器接受的套接字，这就是为什么即使您在浏览器中看到 Not Found，您的请求也永远不会结束。

其次，您的客户端卡住的原因是您用于发送请求 header 的 writeUTF() 方法。似乎这一行 out.writeUTF(CRLF); 并没有真正发送空字符串，而是添加了一些其他与 UTF 相关的字符(您可能会注意到在服务器的控制台输出中)，因此您的服务器陷入 while((headerLine = br.readLine()).length()!=0) 等待客户端发送空字符串，但从未收到它。您需要将 out.writeUTF(CRLF); 替换为 out.writeBytes(CRLF);。

此外，使用 BufferedReader 从套接字接收二进制文件没有什么意义。 Reader 通常与字符输入流一起使用，因此它不适用于您的情况。您可以通过替换以下片段来使用 InputStream:

String headerLine = null;
     while((headerLine = br.readLine()).length()!=0){
            System.out.println("asd"+headerLine);
        }

这样(我选择的缓冲区大小为 4096，您可以将其替换为您喜欢的值):

 int readBytes;
 byte[] cbuf = new byte[4096];
 while((readBytes=inFromServer.read(cbuf, 0, 4096))>-1){
        System.out.println("read: " + readBytes);
    }

注意:您可能很容易注意到，InputStream.read() 不仅会获取文件本身，还会获取 statusLine、contentTypeLine 和两个 CRLF ，因此如果您想将它们与文件分开，您可以先通过发出两个“readLines”来读取它们，然后仅通过 read() 获取文件

关于java - BufferReader 卡在 readline() 中，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53055920/

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