多分辨率图像 API

Java 9 定义多分辨率图像 API，开发者可以很容易的操作和展示不同分辨率的图像了。

以下是多分辨率图像的主要操作方法：

• Image getResolutionVariant(double destImageWidth, double destImageHeight) − 获取特定分辨率的图像变体-表示一张已知分辨率单位为DPI的特定尺寸大小的逻辑图像，并且这张图像是最佳的变体。。
• List<Image> getResolutionVariants() − 返回可读的分辨率的图像变体列表。

import java.io.IOException;
import java.net.URL;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.List;
import java.awt.Image;
import java.awt.image.MultiResolutionImage;
import java.awt.image.BaseMultiResolutionImage;

import javax.imageio.ImageIO;

public class Tester {
   public static void main(String[] args) throws IOException, MalformedURLException {

      List<String> imgUrls = List.of(
         "http://static.nowcoder.com/images/res/logo/logo-v3.png",
         "https://uploadfiles.nowcoder.com/app/android/app.png",
         "https://static.nowcoder.com/images/wx-rcode.jpg");

      List<Image> images = new ArrayList<Image>();

      for (String url : imgUrls) {
         images.add(ImageIO.read(new URL(url)));
      }

      // 读取所有图片
      MultiResolutionImage multiResolutionImage = 
         new BaseMultiResolutionImage(images.toArray(new Image[0]));

      // 获取图片的所有分辨率
      List<Image> variants = multiResolutionImage.getResolutionVariants();

      System.out.println("Total number of images: " + variants.size());

      for (Image img : variants) {
         System.out.println(img);
      }

      // 根据不同尺寸获取对应的图像分辨率
      Image variant1 = multiResolutionImage.getResolutionVariant(156, 45);
      System.out.printf("\nImage for destination[%d,%d]: [%d,%d]", 
         156, 45, variant1.getWidth(null), variant1.getHeight(null));

      Image variant2 = multiResolutionImage.getResolutionVariant(311, 89);
      System.out.printf("\nImage for destination[%d,%d]: [%d,%d]", 311, 89, 
         variant2.getWidth(null), variant2.getHeight(null));

      Image variant3 = multiResolutionImage.getResolutionVariant(622, 178);
      System.out.printf("\nImage for destination[%d,%d]: [%d,%d]", 622, 178, 
         variant3.getWidth(null), variant3.getHeight(null));

      Image variant4 = multiResolutionImage.getResolutionVariant(300, 300);
      System.out.printf("\nImage for destination[%d,%d]: [%d,%d]", 300, 300, 
         variant4.getWidth(null), variant4.getHeight(null));
   }  
}