大家都知道一些比较常用的空间、博客、论坛，设置头像或上传图片到空间的时候都会自动生成帮你生产缩略图，在现在的网络中经常用到，这是用到了图片同比例缩放技术，下面我们通过一个实例来了解一下java中图片上传生成缩略图的方法以及图片上增加水印和调整水印的透明度。
import java.awt.AlphaComposite;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.awt.image.FilteredImageSource;
import java.awt.image.ImageFilter;
import java.awt.image.ImageProducer;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
public class ImageUtils {
/**
* 按源图比例缩放，生成高质量缩略图
*
* @param imageFile
* 源图文件
* @param thumbnailFile
* 要保存到的缩略图文件
* @param maxWidth
* 缩略图的最大宽度
* @param maxHeight
* 缩略图的最大高度
* @throws IOException
* 读取源图imageFile出错，或者用户指定的thumbnailFile无法被创建时
*/
public static void createThumbnail(File imageFile, File thumbnailFile,
int maxWidth, int maxHeight) throws IOException {
if (imageFile == null) {
throw new IllegalArgumentException("图片文件不能为空!");
}
if (thumbnailFile == null) {
throw new IllegalArgumentException("缩略图文件不能为空!");
}
if (maxWidth <= 0) {
throw new IllegalArgumentException("宽度必须大于0");
}
if (maxHeight <= 0) {
throw new IllegalArgumentException("高度必须大于0");
}
try {
BufferedImage image = ImageIO.read(imageFile);
/** 源图宽和高 */
int imageWidth = image.getWidth();
int imageHeight = image.getHeight();
if (maxWidth >= imageWidth && maxHeight >= imageHeight)
return;
/** 按比例缩放图像 */
double scaleZ = (double) imageWidth / imageHeight;
if (scaleZ > 0) {
imageWidth = maxWidth;
imageHeight = (int) (maxWidth / scaleZ);
} else {
imageWidth = (int) (maxHeight * scaleZ);
imageHeight = maxHeight;
}
/**根据源图和缩略图宽高生成一张图片 */
ImageFilter filter = new java.awt.image.AreaAveragingScaleFilter(
imageWidth, imageHeight);
ImageProducer producer = new FilteredImageSource(image.getSource(),
filter);
Image newImage = Toolkit.getDefaultToolkit().createImage(producer);
ImageIcon imageIcon = new ImageIcon(newImage);
Image scaleImage = imageIcon.getImage();
BufferedImage thumbnail = new BufferedImage(imageWidth,
imageHeight, BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = thumbnail.createGraphics();
g2d.drawImage(scaleImage, 0, 0, null);
g2d.dispose();
ImageIO.write(thumbnail, "jpeg", thumbnailFile);
} catch (IOException e) {
throw new IOException("不能生产缩略图文件,请检查文件!");
}
}
/**
* 给图片添加水印，并可调节水印图片的透明度
*
* @param tragetFile
* 目标图片文件
* @param watermarkFile
* 水印图片
* @param x
* 水印在目标图片的横坐标
* @param y
* 水印在目标图片的纵坐标
* @param alpha
* 透明度，必须是范围 [0.0, 1.0] 之内（包含边界值）的一个浮点数字，值越小水印透明度越高
* @throws IOException
* 读取目标图片或水印图片出错时
*/
public static void makeWatermark(File tragetFile, File watermarkFile,
int x, int y, float alpha) throws IOException {
if (tragetFile == null) {
throw new IllegalArgumentException("图片文件不能为空");
}
if (watermarkFile == null) {
throw new IllegalArgumentException("缩略图不能为空");
}
if (alpha < 0 || alpha > 1) {
throw new IllegalArgumentException( "alpha必须是在0.0和1.1之间！");
}
try {
Image target = ImageIO.read(tragetFile);
int targetWidth = target.getWidth(null);
int targetHeight = target.getHeight(null);
Image watermark = ImageIO.read(watermarkFile);
int waterWidth = watermark.getWidth(null);
int waterHeight = watermark.getHeight(null);
BufferedImage bufferedImage = new BufferedImage(targetWidth,
targetHeight, BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = bufferedImage.createGraphics();
/** 从(0,0)坐标开始，把目标图像画进去 */
g2d.drawImage(target, 0, 0, targetWidth, targetHeight, null);
/** 透明度设置 */
g2d.setComposite(AlphaComposite.getInstance(
AlphaComposite.SRC_ATOP, alpha));
/** 根据制定坐标(x,y)，把水印图像画进去 */
g2d.drawImage(watermark, x, y, waterWidth, waterHeight, null);
g2d.dispose();
ImageIO.write(bufferedImage, "jpeg", tragetFile);
} catch (IOException e) {
throw new IOException("不能读取文件,请检查目标文件及水印文件!");
}
}
public static void main(String[] args) {
try {
File file1 = new File("F:\\walerjava.gif");
createThumbnail(file1, new File("F:\\wj2.gif"), 50, 50);
} catch (IOException e) {
e.printStackTrace();
}
}
}