从套接字读取

Question

我在让这个简单的类工作时遇到问题。它基本上连接到 IMAP 服务器并读取横幅。但是在阅读了所有字符之后，它有点悬。在调试器中，我可以单步执行 while 循环并查看正在读取所有字符并最终退出循环。但是最后一个 System.out.println 语句永远不会到达。

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.InputStreamReader;
import java.net.Socket;


public class TestClient
{

    /**

        @param args

     */
    public static void main( String[] args ) throws Exception
    {

        Socket socket = new Socket( "imap.1and1.com", 143 );

        DataOutputStream os = new DataOutputStream( socket.getOutputStream() );
        BufferedReader reader = new BufferedReader( new InputStreamReader( socket.getInputStream() ) );

        StringBuilder sb = new StringBuilder();
        char ch = (char) reader.read();
        while ( ch != -1 ) {
            sb.append( ch );
            ch = (char) reader.read();

        }

        System.out.println( sb.toString() ); /// <--- never prints anything and program just hangs..
    }

}

Answer 1

如果没有要读取的数据，read 函数会阻塞，只有在 readStream 关​​闭或套接字连接断开时才会出现。您应该做的是创建一个协议，在完全读取数据后断开连接。即你应该跳出循环

• 在所有数据都已完成后以某种方式断开连接 已读取（为此您必须确定所有数据已被读取）

• 如果您已经阅读了一些之前同意的内容，请自行退出循环 “消息结束”字符串..

还有一件事，由于 read() 阻塞，等待更多数据，建议你应该在后台线程中读取..

Answer 2

好的，这就是我为解决我的特定问题所做的。请注意，使用 ready() 或 available() 方法并不总是可靠的。特别是如果服务器要发送数据，暂停然后发送更多数据。就我而言，它可以工作，因为我不希望服务器在响应过程中停止并再次重新启动。

代码显然没有针对实际使用进行优化。

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.Socket;

/**
        @author Mir Shafiqul Islam <mislam@mirislam.comt>

 */
public class TestClient
{

    /**

        @param args

     */
    public static void main( String[] args ) throws Exception
    {
        // Open the socket
        Socket socket = new Socket( "localhost", 25143 );
        // Get a buffered reader
        BufferedReader reader = new BufferedReader( new InputStreamReader( socket.getInputStream() ) );
        // At this point it is too early to read. So it most likely return false
        System.out.println( "Buffer Reader ready? " + reader.ready()); 
        // StringBuilder to hold the response
        StringBuilder sb = new StringBuilder();
        // Indicator to show if we have started to receive data or not
        boolean dataStreamStarted = false;
        // How many times we went to sleep waiting for data
        int sleepCounter = 0;
        // How many times (max) we will sleep before bailing out
        int sleepMaxCounter = 50;
        // Sleep max counter after data started
        int sleepMaxDataCounter = 3;
        // How long to sleep for each cycle
        int sleepTime = 50;
        // Start time
        long startTime = System.currentTimeMillis();
        // This is a tight loop. Not sure what it will do to CPU
        while( true ) {
            if ( reader.ready() )
            {
                sb.append( (char) reader.read() );
                // Once started we do not expect server to stop in the middle and restart
                dataStreamStarted = true; 
            } else {
                Thread.sleep( sleepTime );
                if ( dataStreamStarted && (sleepCounter >= sleepMaxDataCounter) ) {
                    System.out.println( "Reached max sleep time of " + (sleepMaxDataCounter*sleepTime) + " ms after data started" );
                    break;
                } else {
                    if (sleepCounter >= sleepMaxCounter) {
                        System.out.println( "Reached max sleep time of " + (sleepMaxCounter*sleepTime) + " ms. Bailing out" );
                        // Reached max timeout waiting for data. Bail..
                        break;
                    }
                }
                sleepCounter++;
            }

        }
        long endTime = System.currentTimeMillis();

        System.out.println( sb.toString() );
        System.out.println( "Time " + (endTime-startTime));
    }

}