关于redis:聊聊RespCommand

序

本文次要钻研一下 RespCommand

RespCommand

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/command/RespCommand.java

@FunctionalInterface
public interface RespCommand {RedisToken execute(Request request);
}

• RespCommand 定义了 execute 办法，接管 Request 参数，返回 RedisToken

Request

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/command/Request.java

public interface Request {String getCommand();
  ImmutableArray<SafeString> getParams();
  SafeString getParam(int i);
  Option<SafeString> getOptionalParam(int i);
  int getLength();
  boolean isEmpty();
  Session getSession();
  ServerContext getServerContext();
  boolean isExit();}

• Request 接口定义了 getCommand、getParams、getParam、getOptionalParam、getLength、isEmpty、getSession、getServerContext、isExit 办法

DefaultRequest

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/command/DefaultRequest.java

public class DefaultRequest implements Request {

  private final SafeString command;

  private final ImmutableArray<SafeString> params;

  private final Session session;

  private final ServerContext server;

  public DefaultRequest(ServerContext server, Session session, SafeString command, ImmutableArray<SafeString> params) {
    this.server = server;
    this.session = session;
    this.command = requireNonNull(command);
    this.params = requireNonNull(params);
  }

  @Override
  public String getCommand() {return command.toString();
  }

  @Override
  public ImmutableArray<SafeString> getParams() {return params;}

  @Override
  public SafeString getParam(int i) {if (i < params.size()) {return params.get(i);
    }
    return null;
  }

  @Override
  public Option<SafeString> getOptionalParam(int i) {return Option.of(() -> getParam(i));
  }

  @Override
  public int getLength() {return params.size();
  }

  @Override
  public boolean isEmpty() {return params.isEmpty();
  }

  @Override
  public boolean isExit() {return command.toString().equalsIgnoreCase("quit");
  }

  @Override
  public Session getSession() {return session;}

  @Override
  public ServerContext getServerContext() {return server;}

  @Override
  public String toString() {return command + "[" + params.size() + "]:" + params;
  }
}

• DefaultRequest 实现了 Request 接口，它定义了 command、params、session、server 属性，均在结构器中传入

CommandSuite

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/command/CommandSuite.java

public class CommandSuite {private static final Logger LOGGER = LoggerFactory.getLogger(CommandSuite.class);

  private final Map<String, Class<?>> metadata = new HashMap<>();
  private final Map<String, RespCommand> commands = new HashMap<>();

  private final NullCommand nullCommand = new NullCommand();

  private final CommandWrapperFactory factory;

  public CommandSuite() {this(new DefaultCommandWrapperFactory());
  }

  public CommandSuite(CommandWrapperFactory factory) {
    this.factory = factory;
    addCommand(PingCommand.class);
    addCommand(EchoCommand.class);
    addCommand(QuitCommand.class);
    addCommand(TimeCommand.class);
  }

  public RespCommand getCommand(String name) {return commands.getOrDefault(name.toLowerCase(), nullCommand);
  }

  public boolean isPresent(String name, Class<? extends Annotation> annotationClass) {return getMetadata(name).isAnnotationPresent(annotationClass);
  }

  public boolean contains(String name) {return commands.get(name) != null;
  }

  protected void addCommand(Class<?> clazz) {Try.of(clazz::newInstance)
       .onSuccess(this::processCommand)
       .onFailure(e -> LOGGER.error("error loading command:" + clazz.getName(), e));
  }

  protected void addCommand(String name, RespCommand command) {commands.put(name.toLowerCase(), factory.wrap(command));
  }

  private void processCommand(Object command) {Class<?> clazz = command.getClass();
    Command annotation = clazz.getAnnotation(Command.class);
    if (annotation != null) {commands.put(annotation.value(), factory.wrap(command));
      metadata.put(annotation.value(), clazz);
    } else {LOGGER.warn("annotation not present at {}", clazz.getName());
    }
  }

  private Class<?> getMetadata(String name) {return metadata.getOrDefault(name.toLowerCase(), Void.class);
  }
}

• CommandSuite 的结构器增加了 PingCommand、EchoCommand、QuitCommand、TimeCommand 四个 command；addCommand 办法将 factory.wrap(command) 的命令放入 commands 中

CommandWrapperFactory

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/command/CommandWrapperFactory.java

public interface CommandWrapperFactory {RespCommand wrap(Object command);
}

• CommandWrapperFactory 定义了 wrap 办法，将 command 包装为 RespCommand

DefaultCommandWrapperFactory

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/command/DefaultCommandWrapperFactory.java

public class DefaultCommandWrapperFactory implements CommandWrapperFactory {
  @Override
  public RespCommand wrap(Object command) {if (command instanceof RespCommand) {return new CommandWrapper((RespCommand) command);
    }
    throw new IllegalArgumentException("must implements command interface");
  }
}

• DefaultCommandWrapperFactory 实现了 CommandWrapperFactory 接口，其 wrap 办法应用 CommandWrapper 包装 RespCommand

CommandWrapper

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/command/CommandWrapper.java

public class CommandWrapper implements RespCommand {

  private int params;

  private final RespCommand command;

  public CommandWrapper(RespCommand command) {
    this.command = command;
    ParamLength length = command.getClass().getAnnotation(ParamLength.class);
    if (length != null) {this.params = length.value();
    }
  }

  @Override
  public RedisToken execute(Request request) {if (request.getLength() < params) {return error("ERR wrong number of arguments for'" + request.getCommand() + "'command");
    }
    return command.execute(request);
  }
}

• CommandWrapper 会读取 ParamLength 注解，若读的到则将注解的 value 值赋值给 params，用于 execute 办法对 request 的参数长度进行校验

小结

RespCommand 定义了 execute 办法，接管 Request 参数，返回 RedisToken；CommandSuite 的结构器增加了 PingCommand、EchoCommand、QuitCommand、TimeCommand 四个 command；addCommand 办法将 factory.wrap(command) 的命令放入 commands 中；DefaultCommandWrapperFactory 实现了 CommandWrapperFactory 接口，其 wrap 办法应用 CommandWrapper 包装 RespCommand；CommandWrapper 会读取 ParamLength 注解，若读的到则将注解的 value 值赋值给 params，用于 execute 办法对 request 的参数长度进行校验

doc

• RespCommand