使用 BufferedImage 将图像加载到 Java 中 - Oracle 教程

Question

I'm a beginner in Java and I would like to load an image with this script:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;

/**
 * This class demonstrates how to load an Image from an external file
 */
public class LoadImageApp extends Component {

BufferedImage img;

public void paint(Graphics g) {
    g.drawImage(img, 0, 0, null);
}

public LoadImageApp() {
   try {
       img = ImageIO.read(getClass().getResource("/resources/java.png"));//cannot found image
   } catch (IOException e) {
   }

}

public Dimension getPreferredSize() {
    if (img == null) {
         return new Dimension(100,100);
    } else {
       return new Dimension(img.getWidth(null), img.getHeight(null));
   }
}

public static void main(String[] args) {

    JFrame f = new JFrame("Load Image Sample");

    f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

    f.add(new LoadImageApp());
    f.pack();
    f.setVisible(true);
}
}

Then I put a picture on a folder resource "resources", change the name of the location of the picture like "/resources/java.png" and when I compile, there is an empty window without image.

You can see error here : https://ibb.co/ysjNyQw

Answer 1

The first thing you're going to want to do is do some research into "embedded resources", for example

I don't use Eclipse, I use Netbeans, but the process should be the same

As you can see, I've placed my image in the resources package within the projects "sources". This will ensure that it's available at runtime via the class path search mechanism (and embedded within the resulting Jar file when I export it).

I then used a JLabel to display it...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    try {
                        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                        ex.printStackTrace();
                    }

                    BufferedImage image = ImageIO.read(getClass().getResource("/resources/java.png"));
                    JLabel label = new JLabel(new ImageIcon(image));

                    JFrame frame = new JFrame("Testing");
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.add(label);
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (IOException ex) {
                    Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        });
    }
}

Now, if you want to continue using a custom painting route, I suggest having a read of:

• Performing Custom Painting
• Painting in AWT and Swing

to get a better understanding of how painting works in Swing and how you should work with it