等比例缩小图片详解编程语言

package com.henu.test; 
import java.awt.Color; 
import java.awt.Graphics; 
import java.awt.Image; 
import java.awt.image.BufferedImage; 
import java.io.File; 
import java.io.IOException; 
import java.util.Arrays; 
import javax.imageio.ImageIO; 
import org.slf4j.Logger; 
import org.slf4j.LoggerFactory; 
public class ImageUtil { 
private Logger log = LoggerFactory.getLogger(getClass()); 
private static String DEFAULT_PREVFIX = "thumb_"; 
private static Boolean DEFAULT_FORCE = false;//建议该值为false 
/** 
* <p>Title: thumbnailImage</p> 
* <p>Description: 根据图片路径生成缩略图 </p> 
* @param imagePath    原图片路径 
* @param w            缩略图宽 
* @param h            缩略图高 
* @param prevfix    生成缩略图的前缀 
* @param force        是否强制按照宽高生成缩略图(如果为false，则生成最佳比例缩略图) 
*/ 
public void thumbnailImage(String imagePath, int w, int h, String prevfix, boolean force){ 
File imgFile = new File(imagePath); 
if(imgFile.exists()){ 
try { 
// ImageIO 支持的图片类型 : [BMP, bmp, jpg, JPG, wbmp, jpeg, png, PNG, JPEG, WBMP, GIF, gif] 
String types = Arrays.toString(ImageIO.getReaderFormatNames()); 
String suffix = null; 
// 获取图片后缀 
if(imgFile.getName().indexOf(".") > -1) { 
suffix = imgFile.getName().substring(imgFile.getName().lastIndexOf(".") + 1); 
}// 类型和图片后缀全部小写，然后判断后缀是否合法 
if(suffix == null || types.toLowerCase().indexOf(suffix.toLowerCase()) < 0){ 
log.error("Sorry, the image suffix is illegal. the standard image suffix is {}." + types); 
return ; 
} 
log.debug("target image's size, width:{}, height:{}.",w,h); 
Image img = ImageIO.read(imgFile); 
if(!force){ 
// 根据原图与要求的缩略图比例，找到最合适的缩略图比例 
int width = img.getWidth(null); 
int height = img.getHeight(null); 
if((width*1.0)/w < (height*1.0)/h){ 
if(width > w){ 
h = Integer.parseInt(new java.text.DecimalFormat("0").format(height * w/(width*1.0))); 
log.debug("change image's height, width:{}, height:{}.",w,h); 
} 
} else { 
if(height > h){ 
w = Integer.parseInt(new java.text.DecimalFormat("0").format(width * h/(height*1.0))); 
log.debug("change image's width, width:{}, height:{}.",w,h); 
} 
} 
} 
BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB); 
Graphics g = bi.getGraphics(); 
g.drawImage(img, 0, 0, w, h, Color.LIGHT_GRAY, null); 
g.dispose(); 
String p = imgFile.getPath(); 
// 将图片保存在原目录并加上前缀 
ImageIO.write(bi, suffix, new File(p.substring(0,p.lastIndexOf(File.separator)) + File.separator + prevfix +imgFile.getName())); 
log.debug("缩略图在原路径下生成成功"); 
} catch (IOException e) { 
log.error("generate thumbnail image failed.",e); 
} 
}else{ 
log.warn("the image is not exist."); 
} 
} 
public static void main(String[] args) { 
new ImageUtil().thumbnailImage("D:/test/1.jpg", 510, 288, DEFAULT_PREVFIX,DEFAULT_FORCE); 
} 
}