Question

答案是我的其他评论

我有一个问题，我通过DatagramPacket和DatagramSocket将用户和密码字符串发送到远程计算机，我想在数据库中执行select语句，但问题是接收到的字符串看起来像是什么在这里有一些代码：

//build and send method
public void packetCompose(String user, String password) {
    try {
        byte[] userBytes = user.getBytes();
        byte[] passwordBytes = password.getBytes();
        byte[] buf = new byte[256];
        System.arraycopy( userBytes    , 0, buf,   0, Math.min( userBytes.length, 128 ) );
        System.arraycopy( passwordBytes, 0, buf, 128, Math.min( userBytes.length, 128 ) );

        DatagramPacket packet = new DatagramPacket(buf, 256, serverAddress, 4445);
        socket.send(packet);
    } catch (SocketException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

现在分解方法

public void packetDecompose(DatagramPacket packet) {
            // packet has this structure
            // 128 bytes            user String
            // 128 bytes            password String
            clientAddress = packet.getAddress();
            String user = new String(packet.getData(),0,128);
            String password = new String(packet.getData(),128,128);
            System.out.println("Packet content: \nuser: "+user+"\npassword: "+password);
            boolean exists = userExists(user, password);
            byte[] buf = new byte[128];
            if(exists) {
                    System.out.println("User exists");
                    System.arraycopy( accessGranted.getBytes(), 0, buf, 0, Math.min(
accessGranted.getBytes().length, 128 ) );
                    send(new DatagramPacket(buf, 128, clientAddress, 4445));
            } else {
                    System.out.println("User does not exist");
                    System.arraycopy( accessDenied.getBytes(), 0, buf, 0, Math.min(
accessDenied.getBytes().length, 128 ) );
                    send(new DatagramPacket(buf, 128, clientAddress, 4445));
            }

    }

    public boolean userExists(String user, String password) {
            boolean exists = false;
            System.out.println("user: "+user.equals("asdf"));
            System.out.println(" pass: "+password.equals("asdf"));
            try {

                    ResultSet result = dataBase.Select("SELECT ipaddress FROM users
WHERE name='"+user+"' AND pass='"+password+"'");
                    while(result.next()) {
                            exists = true;
                    }
            } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
            }
            return exists;
    }

我通过应用程序的界面引入asdf作为用户和密码，所以行：

System.out.println("user: "+user.equals("asdf"));
System.out.println(" pass: "+password.equals("asdf"));

应该打印为true，但是它们打印为false。有什么建议吗？提前谢谢大家

Answer 1

您似乎拥有长度为128个字节的字符串。这些字符串具有普通文本，后跟空字节，您可能无法在屏幕上看到它们。

我建议你使用DataOutputStream.writeUTF（）来编写字符串，这样它就会发送长度，只发送字符串中实际的字节（没有空填充）。

Answer 2

我终于设法解决了这个问题，感谢Peter Lawrey提供了一些帮助。

您必须插入包含用户String长度的第一个字节，并且与pasword相同，因此在分解数据包时，您可以获得没有空填充的用户和密码。这是代码：

Compossing：

public void packetCompose(String user, String password) {
    try {
        byte[] userBytes = user.getBytes();
        byte[] passwordBytes = password.getBytes();
        byte[] buf = new byte[256];
        //first byte contain user length in bytes
        System.arraycopy( new byte[]{(byte)userBytes.length}    , 0, buf, 0, 1 );
        // Then the user
        System.arraycopy( userBytes    , 0, buf,   1, userBytes.length );
        //a byte containing password length in bytes after user
        System.arraycopy( new byte[]{(byte)passwordBytes.length} ,0 , buf,   userBytes.length +1, 1);
        // password
        System.arraycopy( passwordBytes , 0, buf,   userBytes.length+2, passwordBytes.length );

        DatagramPacket packet = new DatagramPacket(buf, 256, serverAddress, 4445);
        socket.send(packet);
    } catch (SocketException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } 
}

Decompossing：

public void packetDecompose(DatagramPacket packet) {
            // packet has this structure
            // 1 byte                       user length in bytes
            // ? bytes                      user String
            // 1 byte                       password length in byte
            // ? bytes              password String
            clientAddress = packet.getAddress();
            byte[] userLength = new byte[]{packet.getData()[0]};
            String user = new String(packet.getData(), 1, (int)userLength[0]);
            byte[] passwordLength = new byte[]{packet.getData()[(int)userLength[0]+1]};
            String password = new String(packet.getData(), (int)userLength[0]+2, (int)passwordLength[0]);
            System.out.println("Packet content: \nuser: "+user+"\npassword: "+password);
            boolean exists = userExists(user, password);
            byte[] buf = new byte[128];
            if(exists) {
                    System.out.println("User exists");
                    System.arraycopy( accessGranted.getBytes(), 0, buf, 0, Math.min(
accessGranted.getBytes().length, 128 ) );
                    send(new DatagramPacket(buf, 128, clientAddress, 4445));
            } else {
                    System.out.println("User does not exist");
                    System.arraycopy( accessDenied.getBytes(), 0, buf, 0, Math.min(
accessDenied.getBytes().length, 128 ) );
                    send(new DatagramPacket(buf, 128, clientAddress, 4445));
            }

    }

DatagramPacket和DatagramSocket发送的字符串不等于其自身的文字表示

2 个答案: