缩略图片

package utils;

import java.awt.Image;

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

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGEncodeParam;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class Photo {

    public static void reduceImg(OutputStream out, String path, int width, int height) {
        try {
            File srcfile = new File(path);
            if (!srcfile.exists()) {
                System.out.println("缩放图片文件不存在！");
                return;
            }
            BufferedImage src = ImageIO.read(srcfile);

            // 得到原始宽和高
            int w = src.getWidth();
            int h = src.getHeight();
            double sx = (double) width / w;
            double sy = (double) height / h;
            if (sx < sy) {
                sy = sx;
                height = (int) (sy * h);
            } else {
                sx = sy;
                width = (int) (sy * w);
            }
            System.out.println(String.format("%s, %s", w, h));
            System.out.println(String.format("%s, %s", width, height));

            BufferedImage source = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
            // Image.SCALE_SMOOTH 的缩略算法 生成缩略图片的平滑度的 优先级比速度高 生成的图片质量比较好 但速度慢
            source.getGraphics().drawImage(
                    src.getScaledInstance(width, height, Image.SCALE_SMOOTH), 0, 0, null);
            JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
            JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(source);
            param.setQuality(70f, true);
            encoder.encode(source, param);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    /**
     * 根据图片路径 读取图片文件
     * 
     * @param fileName
     * @return
     */
    public static BufferedImage readImage(String fileName) {
        BufferedImage bi = null;
        try {
            bi = ImageIO.read(new File(fileName));
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
        return bi;
    }

    /**
     * 生成新的图片文件
     * 
     * @param im
     * @param formatName
     * @param fileName
     * @return
     */
    public static boolean writeImage(RenderedImage im, String formatName, String fileName) {
        boolean result = false;
        try {
            result = ImageIO.write(im, formatName, new File(fileName));
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
        return result;
    }

    /**
     * 转换图片格式 到 jpg
     * 
     * @param im
     * @param fileName
     * @return
     */
    public static boolean writeJPEGImage(RenderedImage im, String fileName) {
        return writeImage(im, "JPEG", fileName);
    }

    /**
     * 转换图片格式 到 gif 不知到好用不
     * 
     * @param im
     * @param fileName
     * @return
     */
    public static boolean writeGIFImage(RenderedImage im, String fileName) {
        return writeImage(im, "GIF", fileName);
    }

    public static boolean writePNGImage(RenderedImage im, String fileName) {
        return writeImage(im, "PNG", fileName);
    }

    public static boolean writeBMPImage(RenderedImage im, String fileName) {
        return writeImage(im, "BMP", fileName);
    }
}

调用：

<%@ page language="java" pageEncoding="utf-8"%>
<%@ page import="utils.Photo"%>
<%@ page import="java.io.OutputStream"%>
<%
response.setHeader("Pragma", "no-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
response.setContentType("image/jpeg");
String path = this.getServletContext().getRealPath("images/photo1.jpg");
OutputStream outputStream = response.getOutputStream();
Photo.reduceImg(outputStream, path, 300, 300);
outputStream.close();
out.clear();
out = pageContext.pushBody();
%>