package com.lin.imagemgr;

import java.awt.Dimension;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.stream.Collectors;
import javax.swing.ImageIcon;
import javax.swing.JLabel;

import net.coobird.thumbnailator.Thumbnails;

public class ImageMgr {
 private static ImageMgr instance = new ImageMgr();
 private ImageMgr() {}
 public static ImageMgr getInstance() {
  return instance;
 }

 //線程池
 private ExecutorService executor = Executors.newFixedThreadPool(8);

 public List<JLabel> loadImages(String path) {
  List<JLabel> images = new ArrayList<>();
  File file = new File(path);
  if (!file.isDirectory()) {
   throw new RuntimeException("need directory!");
  }
  File[] files = file.listFiles(new FilenameFilter() {

   @Override
   public boolean accept(File dir, String name) {
    //thumbnail只支持jpg??
    if (name.endsWith(".jpg")) {
     return true;
    }
    return false;
   }
  });

  //并發加載圖片，并使用Future保存加載結果
  List<Future<MyLabel>> futures = new ArrayList<>();
  for (final File f : files) {
   Future<MyLabel> future = executor.submit(() -> {
    return new MyLabel(f.getName(), f.getAbsolutePath());
   });
   futures.add(future);
  }

  //等待所有并發加載返回結果
  try {
   for (Future<MyLabel> future : futures) {
    MyLabel icon = future.get();
    images.add(icon);
   }
  } catch (InterruptedException e) {
   e.printStackTrace();
  } catch (ExecutionException e) {
   e.printStackTrace();
  }

  //Java8使用stream API 進行排序
  List<JLabel> sortedList = images.stream().sorted().collect(Collectors.toList());

  return sortedList;
 }

 //繼承JLabel并實現Comparable接口，從而對JLabel進行排序
 private static class MyLabel extends JLabel implements Comparable<MyLabel>{
  private static final long serialVersionUID = 1L;
  private String fileName;

  public MyLabel(String fileName, String fullPath) {
   this.fileName = fileName;
   //使用thumbnailator生成縮略圖
   try {
    BufferedImage bufferedImage = Thumbnails.of(fullPath) 
    .size(100, 120)
    .asBufferedImage();
    setIcon(new ImageIcon(bufferedImage));
    setPreferredSize(new Dimension(100, 120));
   } catch (IOException e) {
    e.printStackTrace();
   }
  }

  @Override
  public int compareTo(MyLabel o) {
   int result = this.fileName.compareTo(o.fileName);
   return result;
  }


 }

}

package com.lin.imagemgr;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;

public class MainFrame extends JFrame{
 private static final long serialVersionUID = 1L;
 private JTextField pathField;
 private JButton showBtn;
 private JPanel contentPanel;

 public void init() {
  JPanel topPanel = new JPanel(new FlowLayout(FlowLayout.LEFT, 5, 0));
  topPanel.setPreferredSize(new Dimension(800, 40));
  pathField = new JTextField(50);
  showBtn = new JButton("顯示圖片");
  topPanel.add(pathField);
  topPanel.add(showBtn);
  getContentPane().add(BorderLayout.NORTH, topPanel);
  contentPanel = new JPanel();
  contentPanel.setLayout(new FlowLayout(FlowLayout.LEFT, 5, 5));
  contentPanel.setPreferredSize(new Dimension(750, 1800));
  JScrollPane jsp = new JScrollPane(contentPanel);
  getContentPane().add(BorderLayout.CENTER, jsp);

  showBtn.addActionListener((e) -> {
   try {
    loadImages();
   } catch (Exception ex) {
    ex.printStackTrace();
   }
  });

  setSize(800, 650);
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  setLocationRelativeTo(null);
  setVisible(true);
 }

 public void loadImages() {
  contentPanel.removeAll();
  String path = pathField.getText();
  long start = System.currentTimeMillis();
  List<JLabel> images = ImageMgr.getInstance().loadImages(path);
  for (JLabel label :images) {
   contentPanel.add(label);
  }
  contentPanel.updateUI();
  long end = System.currentTimeMillis();
  System.out.println("加載需要" + (end - start) + "毫秒！");

 }

 public static void main(String[] args) {
  new MainFrame().init();
 }

}