java 图片指定长宽完整代码

在Java中，如果你想要加载图片并设置特定的宽度和高度，通常会使用`BufferedImage`类以及`ImageIO`来操作。以下是一个简单的示例，展示了如何创建一个新的图像，保持原始比例，然后按照指定大小缩放：

import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;

public class ImageResizeExample {
    public static BufferedImage resizeImage(String srcPath, int targetWidth, int targetHeight) {
        File imgFile = new File(srcPath);
        try {
            BufferedImage originalImg = ImageIO.read(imgFile);
            int width = originalImg.getWidth();
            int height = originalImg.getHeight();

            // 创建新的BufferedImage，并设置透明背景
            BufferedImage resizedImg = new BufferedImage(targetWidth, targetHeight, BufferedImage.TYPE_INT_ARGB);

            // 如果原始图像比目标尺寸大，按比例缩放
            if (width > height && width > targetWidth || height > targetHeight) {
                double scaleRatio = Math.min((double)targetWidth / width, (double)targetHeight / height);
                int newWidth = (int)(width * scaleRatio);
                int newHeight = (int)(height * scaleRatio);

                // 使用AffineTransform进行等比例缩放
                AffineTransform at = new AffineTransform();
                at.scale(scaleRatio, scaleRatio);
                at.translate(-(newWidth - targetWidth) / 2, -(newHeight - targetHeight) / 2);
                Graphics2D g2d = resizedImg.createGraphics();
                g2d.drawImage(originalImg, at, null);
                g2d.dispose();
            } else { // 否则，直接复制
                resizedImg.getGraphics().drawImage(originalImg, 0, 0, targetWidth, targetHeight, null);
            }

            return resizedImg;
        } catch (Exception e) {
            System.out.println("Error reading or resizing image: " + e.getMessage());
            return null; // 或者处理异常
        }
    }

    public static void main(String[] args) {
        String srcPath = "path_to_your_image.jpg";
        int targetWidth = 500;
        int targetHeight = 500;
        BufferedImage resizedImg = resizeImage(srcPath, targetWidth, targetHeight);
        if (resizedImg != null) {
            // 现在你可以保存、显示或做其他操作
            save(resizedImg, "resized_" + srcPath);
            // OR
            display(resizedImg);
        }
    }

    // 保存图片到文件的方法
    private static void save(BufferedImage img, String filePath) {
        try {
            ImageIO.write(img, "jpg", new File(filePath));
        } catch (IOException e) {
            System.out.println("Error saving the image: " + e.getMessage());
        }
    }

    // 显示图片的方法（仅作示例，实际应用可能需要窗体或Swing）
    private static void display(BufferedImage img) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JLabel label = new JLabel(new ImageIcon(img));
        frame.add(label);
        frame.pack();
        frame.setVisible(true);
    }
}