java - 来自抽象父类(super class)的抽象方法作为子类中的静态方法

Question

我开发了一个自定义通信协议(protocol)。在此协议(protocol)中，每个数据包由 header 和有效负载组成。每个有效负载包含多个命令。

我想在每个命令(Command0，...，命令 N)中实现静态“解码”方法，因为相同类型的所有命令都以相同的方式解码(它们具有相同的字段结构)。我使用摘要类“Command”作为模板，其中包含一些常见字段和方法以及用于我的命令的抽象“解码”方法。但由于父类(super class)方法是抽象的，Command0、...、CommandN 中的“解码”方法不能是静态的。

有什么解决办法吗？我想避免每次必须解码某些数据包时都实例化每个命令。

作为替代方案，我摆脱了抽象的“解码”方法，并在每个扩展 Command 的命令中包含静态“解码”方法。但是，如果没有父类(super class)或接口(interface)，其他程序员可能会忘记实现解码方法。这种替代方案将导致以下代码:

{
    switch(commandIdentifier)
    {
        case 0:
        {
            Command0 command0 = Command0.decode(dbConnection, header, data, offset);
            payload.getCommands().add(command0);
            break;
        }
        //...
        case N:
        {
            CommandN commandN = CommandN.decode(dbConnection, header, data, offset);
            payload.getCommands().add(commandN);
            break;
        }
        default:
        {
            //some code
        }
    }
}

我首先必须检查命令标识符。

我最初是这样实现这些类的:

public class Packet
{
    private Header header;
    private Payload payload;

    public static Packet decode(Connection dbConnection, byte[] data, int offset) throws Exception
    {
        //...
    }
}

public class Header
{
    public static Header decode(byte[] data, int offset)
    {
        //...
    }
}

public class Payload
{
    private List<Command> commands;
    public static Payload decode(Connection dbConnection, Header header, byte[] data, int offset)
    {
        //iterate over the data bytes to populate commands
    }
}

public abstract class Command
{
    public abstract Command decode(Connection dbConnection, Header header, byte[] data, int offset) throws Exception;
}

public class Command0
{
    int field1;
    String field2;
    float field3;
    public Command decode(Connection dbConnection, Header header, byte[] data, int offset) throws Exception;  //I can't make it static and I'd like to because all commands of class Command0 are decoded the same way.
}

//...

public class Command N
{
    int field1;
    Map<Integer, ConfigBean> field2;
    public Command decode(Connection dbConnection, Header header, byte[] data, int offset) throws Exception;  //I can't make it static and I'd like to because all commands of class CommandN are decoded the same way.
}

Answer 1

您可以有一个 enum 类，其中包含与命令是什么以及如何解码它相关的信息。使用抽象方法而不是静态方法将迫使您为每个方法实现解码:

public enum CommandType {
    COMMAND_0(0) {
        @Override
        public <T extends Command> T decode(Connection dbConnection, ResponseBuilder.Header header, byte[] data, int offset) throws Exception {
            // decode Command 0
            ...
        }
    },
    COMMAND_1(1) {
        @Override
        public <T extends Command> T decode(Connection dbConnection, ResponseBuilder.Header header, byte[] data, int offset) throws Exception {
            // decode Command 1
            ...
        }
    }
    ...
    COMMAND_N(N) {
        @Override
        public <T extends Command> T decode(Connection dbConnection, ResponseBuilder.Header header, byte[] data, int offset) throws Exception {
            // decode Command N
            ...
        }
    }
    ;

    private final int commandIdentifier;

    CommandType(int commandIdentifier) {
        this.commandIdentifier = commandIdentifier;
    }

    public abstract <T extends Command> T decode(Connection dbConnection, ResponseBuilder.Header header, byte[] data, int offset) throws Exception;


    private static Map<Integer, CommandType> map = new HashMap<Integer, CommandType>();
    static {
        for (CommandType commandType : CommandType.values()) {
            if (map.get(commandType.commandIdentifier) != null)
                throw new IllegalStateException("There are several commands with the same identifier");
            map.put(commandType.commandIdentifier, commandType);
        }
    }

    public static CommandType fromIdentifier(int commandIdentifier) throws IllegalArgumentException {
        CommandType commandType = map.get(commandIdentifier);
        if (commandType == null)
            throw new IllegalArgumentException("Unkown command identifier");
        return commandType;
    }

}

之后您可以简单地使用:

Command c = CommandType.fromIdentifier(commandIdentifier).decodedecode(dbConnection, header, data, offset);

我认为这是一种更时尚的处理方式