关于redis:聊聊RedisTokenVisitor

本文次要钻研一下 RedisTokenVisitor

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/protocol/RedisTokenVisitor.java

public interface RedisTokenVisitor<T> {T array(ArrayRedisToken token);
  T status(StatusRedisToken token);
  T string(StringRedisToken token);
  T integer(IntegerRedisToken token);
  T error(ErrorRedisToken token);
  T unknown(UnknownRedisToken token);

  static <T> LambdaRedisTokenVisitor.Builder<T> builder() {return new LambdaRedisTokenVisitor.Builder<>();
  }
}

RedisTokenVisitor 接口定义了 array、status、string、integer、error、unknown 办法，并提供了动态 builder 办法用于创立 LambdaRedisTokenVisitor.Builder

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/protocol/AbstractRedisTokenVisitor.java

public abstract class AbstractRedisTokenVisitor<T> implements RedisTokenVisitor<T> {
  @Override
  public T array(ArrayRedisToken token) {return null;}

  @Override
  public T status(StatusRedisToken token) {return null;}

  @Override
  public T string(StringRedisToken token) {return null;}

  @Override
  public T error(ErrorRedisToken token) {return null;}

  @Override
  public T unknown(UnknownRedisToken token) {return null;}

  @Override
  public T integer(IntegerRedisToken token) {return null;}
}

AbstractRedisTokenVisitor 实现了 RedisTokenVisitor 接口，默认返回 null

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/protocol/LambdaRedisTokenVisitor.java

class LambdaRedisTokenVisitor<T> implements RedisTokenVisitor<T> {

  private Function<ArrayRedisToken, T> onArray;
  private Function<StatusRedisToken, T> onStatus;
  private Function<StringRedisToken, T> onString;
  private Function<ErrorRedisToken, T> onError;
  private Function<IntegerRedisToken, T> onInteger;
  private Function<UnknownRedisToken, T> onUnknown;

  LambdaRedisTokenVisitor(
      Function<ArrayRedisToken, T> onArray,
      Function<StatusRedisToken, T> onStatus,
      Function<StringRedisToken, T> onString,
      Function<ErrorRedisToken, T> onError,
      Function<IntegerRedisToken, T> onInteger,
      Function<UnknownRedisToken, T> onUnknown) {
    this.onArray = onArray;
    this.onStatus = onStatus;
    this.onString = onString;
    this.onError = onError;
    this.onInteger = onInteger;
    this.onUnknown = onUnknown;
  }

  @Override
  public T array(ArrayRedisToken token) {return onArray.apply(token);
  }

  @Override
  public T status(StatusRedisToken token) {return onStatus.apply(token);
  }

  @Override
  public T string(StringRedisToken token) {return onString.apply(token);
  }

  @Override
  public T error(ErrorRedisToken token) {return onError.apply(token);
  }

  @Override
  public T unknown(UnknownRedisToken token) {return onUnknown.apply(token);
  }

  @Override
  public T integer(IntegerRedisToken token) {return onInteger.apply(token);
  }

  public static class Builder<T> {
    private Function<ArrayRedisToken, T> onArray;
    private Function<StatusRedisToken, T> onStatus;
    private Function<StringRedisToken, T> onString;
    private Function<ErrorRedisToken, T> onError;
    private Function<IntegerRedisToken, T> onInteger;
    private Function<UnknownRedisToken, T> onUnknown;

    public Builder<T> onArray(Function<ArrayRedisToken, T> onArray) {this.onArray = requireNonNull(onArray);
      return this;
    }

    public Builder<T> onStatus(Function<StatusRedisToken, T> onStatus) {this.onStatus = requireNonNull(onStatus);
      return this;
    }

    public Builder<T> onString(Function<StringRedisToken, T> onString) {this.onString = requireNonNull(onString);
      return this;
    }

    public Builder<T> onError(Function<ErrorRedisToken, T> onError) {this.onError = requireNonNull(onError);
      return this;
    }

    public Builder<T> onInteger(Function<IntegerRedisToken, T> onInteger) {this.onInteger = requireNonNull(onInteger);
      return this;
    }

    public Builder<T> onUnknown(Function<UnknownRedisToken, T> onUnknown) {this.onUnknown = requireNonNull(onUnknown);
      return this;
    }

    public RedisTokenVisitor<T> build() {
      return new LambdaRedisTokenVisitor<>(safe(onArray), safe(onStatus), safe(onString),
          safe(onError), safe(onInteger), safe(onUnknown));
    }

    private <X> Function<X, T> safe(Function<X, T> function) {return nonNull(function) ? function : x -> null;
    }
  }
}

LambdaRedisTokenVisitor 实现了 RedisTokenVisitor 接口，其结构器要求输出 onArray、onStatus、onString、onError、onInteger、onUnknown 这几个 Function

resp-server-0.16.0/src/main/java/com/github/tonivade/resp/protocol/RedisSerializer.java

public class RedisSerializer {
  private static final byte ARRAY = '*';
  private static final byte ERROR = '-';
  private static final byte INTEGER = ':';
  private static final byte SIMPLE_STRING = '+';
  private static final byte BULK_STRING = '$';

  private static final byte[] DELIMITER = new byte[] {'\r', '\n'};
  private static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");

  private ByteBufferBuilder builder = new ByteBufferBuilder();

  public byte[] encodeToken(RedisToken msg) {msg.accept(new AbstractRedisTokenVisitor<Void>() {
      @Override
      public Void string(StringRedisToken token) {addBulkStr(token.getValue());
        return null;
      }

      @Override
      public Void status(StatusRedisToken token) {addSimpleStr(token.getValue());
        return null;
      }

      @Override
      public Void integer(IntegerRedisToken token) {addInt(token.getValue());
        return null;
      }

      @Override
      public Void error(ErrorRedisToken token) {addError(token.getValue());
        return null;
      }

      @Override
      public Void array(ArrayRedisToken token) {addArray(token.getValue());
        return null;
      }
    });
    return builder.build();}

  private void addBulkStr(SafeString str) {if (str != null) {builder.append(BULK_STRING).append(str.length()).append(DELIMITER).append(str);
    } else {builder.append(BULK_STRING).append(-1);
    }
    builder.append(DELIMITER);
  }

  private void addSimpleStr(String str) {builder.append(SIMPLE_STRING).append(str.getBytes()).append(DELIMITER);
  }

  private void addInt(Integer value) {builder.append(INTEGER).append(value).append(DELIMITER);
  }

  private void addError(String str) {builder.append(ERROR).append(str.getBytes()).append(DELIMITER);
  }

  private void addArray(Sequence<RedisToken> array) {if (array != null) {builder.append(ARRAY).append(array.size()).append(DELIMITER);
      for (RedisToken token : array) {builder.append(new RedisSerializer().encodeToken(token));
      }
    } else {builder.append(ARRAY).append(0).append(DELIMITER);
    }
  }

  private static class ByteBufferBuilder {
    private static final int INITIAL_CAPACITY = 1024;

    private ByteBuffer buffer = ByteBuffer.allocate(INITIAL_CAPACITY);

    private ByteBufferBuilder append(int i) {append(String.valueOf(i));
      return this;
    }

    private ByteBufferBuilder append(String str) {append(str.getBytes(DEFAULT_CHARSET));
      return this;
    }

    private ByteBufferBuilder append(SafeString str) {append(str.getBytes());
      return this;
    }

    private ByteBufferBuilder append(byte[] buf) {ensureCapacity(buf.length);
      buffer.put(buf);
      return this;
    }

    public ByteBufferBuilder append(byte b) {ensureCapacity(1);
      buffer.put(b);
      return this;
    }

    private void ensureCapacity(int len) {if (buffer.remaining() < len) {growBuffer(len);
      }
    }

    private void growBuffer(int len) {int capacity = buffer.capacity() + Math.max(len, INITIAL_CAPACITY);
      buffer = ByteBuffer.allocate(capacity).put(build());
    }

    public byte[] build() {byte[] array = new byte[buffer.position()];
      buffer.rewind();
      buffer.get(array);
      return array;
    }
  }
}

RedisSerializer 的 encodeToken 办法创立了匿名 AbstractRedisTokenVisitor；其 string 办法执行 addBulkStr(token.getValue())；其 status 办法执行 addSimpleStr(token.getValue())；其 integer 办法执行 addInt(token.getValue())；其 error 办法执行 addError(token.getValue())；其 array 办法执行 addArray(token.getValue())

RedisTokenVisitor 接口定义了 array、status、string、integer、error、unknown 办法，并提供了动态 builder 办法用于创立 LambdaRedisTokenVisitor.Builder；目前 RedisSerializer 的 encodeToken 办法创立了匿名 AbstractRedisTokenVisitor，提供了一个实现。不过目前这个接口的设计有点坏滋味，实践上应该把差别提取到泛型中。

RedisTokenVisitor

关于redis:聊聊RedisTokenVisitor

序

RedisTokenVisitor

AbstractRedisTokenVisitor

LambdaRedisTokenVisitor

RedisSerializer

小结

doc