设计模式：如何为方法添加可选参数？

Question

我有一个实用程序类：

public class ImageCompressionUtil {

  public static void compressor(InputStream image, OutputStream outputStream, double quality,
      String outputFormat) throws IOException {
    Thumbnails.of(image).scale(1).outputQuality(quality).outputFormat(outputFormat).
        toOutputStream(outputStream);
  }

  public static void compressor(byte[] image, OutputStream outputStream, double quality,
      String outputFormat) throws IOException {
    ByteArrayInputStream inputStream = new ByteArrayInputStream(image);
    Thumbnails.of(inputStream).scale(1).outputQuality(quality).
        outputFormat(outputFormat).toOutputStream(outputStream);
  }

  public static byte[] compressor(InputStream image, double quality, String outputFormat)
      throws IOException {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    Thumbnails.of(image).scale(1).outputQuality(quality).
        outputFormat(outputFormat).toOutputStream(outputStream);
    return outputStream.toByteArray();
  }

  public static byte[] compressor(byte[] image, double quality, String outputFormat) throws IOException {
    ByteArrayInputStream inputStream = new ByteArrayInputStream(image);
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    Thumbnails.of(inputStream).scale(1).outputQuality(quality).
        outputFormat(outputFormat).toOutputStream(outputStream);
    return outputStream.toByteArray();
  }
}

在这些方法中，我们可以看到一些重复的参数，例如outputStream,quality,outputFormat。 如何重写这个类，以便我可以像这样的模式使用这个类：

// no outputstream/quality/outputFormat specified, default values are used;
ImageCompressionUtil.compressor(image);

// specifiy outputstream or quality or outputFormat
ImageCompressionUtil.compressor(image, outputstream);
ImageCompressionUtil.compressor(image).quality(quality);
ImageCompressionUtil.compressor(image).outputFormat(outputFormat);

// both quality and outputFormat are specified
ImageCompressionUtil.compressor(image).quality(quality).outputFormat(outputFormat);

...

Answer 1

是的：它看起来像构建器模式。

您只需要两个 compressor 方法，它们将返回 Compressor 类（构建器）的实例：

public class ImageCompressionUtil {
    public Compressor compressor(InputStream image) {
        return new Compressor(image);
    }

    public Compressor compressor(byte[] image) {
        return new Compressor(new ByteArrayInputStream(image));
    }
}

Compressor 类如下所示：

public class Compressor {
    private final Thumbnail thumbnail;

    public Compressor(InputStream image) {
        this.thumbnail = Thumbnail.of(image).scale(1);
    }

    public Compressor quality(double quality) {
        thumbnail.outputQuality(quality);
        return this;
    }

    public Compressor outputFormat(String format) {
        thumbnail.outputFormat(format);
        return this;
    }

    public void writeTo(OutputStream outputStream) {
        thumbnail.toOutputStream(outputStream);
    }

    public byte[] toBytes() {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        writeTo(out);
        return out.toByteArray();
    }
}

因此，您将首先创建一个压缩器，然后设置参数，然后将结果写入 OutputStream 或将其作为字节数组获取。

不清楚的是哪个类应该关闭InputStream。

请注意Compressor 类与我所说的Thumbnail 类（由Thumbnails.of() 返回的内容）并没有太大区别，您可以直接返回Thumbnails.of(image).scale(1) 的结果而不是创建另一个类.