Java提取pcap文件中smtp流的有效载荷

要提取pcap文件中SMTP流的有效载荷，你可以使用Java中的pcap4j库。以下是一个简单的示例代码，可以提取SMTP流并打印有效载荷：

import java.io.EOFException;
import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.concurrent.TimeoutException;

import org.pcap4j.core.BpfProgram.BpfCompileMode;
import org.pcap4j.core.PacketListener;
import org.pcap4j.core.PcapHandle;
import org.pcap4j.core.PcapHandle.TimestampPrecision;
import org.pcap4j.core.PcapNativeException;
import org.pcap4j.core.Pcaps;
import org.pcap4j.packet.Packet;
import org.pcap4j.packet.TcpPacket;
import org.pcap4j.packet.namednumber.TcpPort;

public class SmtpPayloadExtractor {

    private static final int READ_TIMEOUT = 10; // milliseconds
    private static final int SNAPLEN = 65536; // bytes
    private static final int TIMEOUT = 10; // seconds
    
    public static void main(String[] args) throws PcapNativeException, UnknownHostException {
        PcapHandle handle = Pcaps.openOffline("path/to/pcap/file", TimestampPrecision.NANO);
        handle.setFilter("tcp and port 25", BpfCompileMode.OPTIMIZE);
        PacketListener listener = new PacketListener() {
            @Override
            public void gotPacket(Packet packet) {
                TcpPacket tcpPacket = packet.get(TcpPacket.class);
                if (tcpPacket != null && tcpPacket.getHeader().getDstPort().equals(TcpPort.SMTP)) {
                    byte[] payload = tcpPacket.getPayload().getRawData();
                    System.out.println(new String(payload));
                }
            }
        };
        try {
            handle.loop(-1, listener);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (PcapNativeException e) {
            e.printStackTrace();
        } catch (EOFException e) {
            e.printStackTrace();
        }
        handle.close();
    }
}

在上面的代码中，我们使用PcapHandle打开pcap文件，设置过滤器以仅捕获TCP端口25的流量。然后，我们定义一个PacketListener，它会在每个匹配的数据包中提取有效载荷，并将其输出到控制台。最后，我们使用handle.loop方法启动捕获循环，并在循环结束后关闭handle。