java 怎么 png转jpg
java   怎么   png转jpg

------解决方案--------------------
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.net.URL;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.imageio.ImageIO;

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

public class ImageUtil {

/**
* @param args
*/
public static void main(String[] args) {
try{
CopyImageFromURL( "E:/cat.png ", "E:/111/aaa.jpg ");
CopyImageFromURL( "http://www.csdn.net/ui/styles/public_header_footer/logo_csdn.gif ", "E:/111/logo_csdn.jpg ");
}catch(Exception e){
e.printStackTrace();
}
}

/**
*
* @param imageURL 输入图片的URL完整路径，可以是本地文件，也可以是网路上的文件
* @param localPath 保存在本地的路径
* @throws Exception
*/
public static void CopyImageFromURL(String imageURL, String localPath)
throws Exception {
// 取得文件后缀名
String tmpImageURL = imageURL.toLowerCase();
String regex = "(\\.)(gif|bmp|png|dib|jpg|jpeg|jfif) ";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(tmpImageURL);
if (!matcher.find()) {
throw new Exception( "不支持该格式文件. ");
}
URL url;
if (imageURL.toLowerCase().startsWith( "http ")) {// http url
url = new URL(imageURL);
} else {// 文件url
String tmpUrl = imageURL.toLowerCase();
String beginer = tmpUrl.split( "/ ")[0];
if (beginer.matches( "[c-o]: ")) {// 路径支持到c:d:....o:
url = new File(imageURL).toURL();
} else {
throw new Exception( "无法解析文件URL. ");
}
}
BufferedImage src = ImageIO.read(url);
int width = src.getWidth(null);
int height = src.getHeight(null);
// 保存图像到本地
int lastSep1 = localPath.lastIndexOf( "/ ");
int lastSep2 = localPath.lastIndexOf( "\\ ");
int lastSep = (lastSep1> =lastSep2?lastSep1:lastSep2);
String path = localPath.substring(0,lastSep);
File localDir = new File(path);
if (!localDir.exists()) {
localDir.mkdirs();
}
BufferedImage outImg = new BufferedImage(width, height,src.getType());
outImg.getGraphics().drawImage(src, 0, 0, width, height, null);
FileOutputStream out = new FileOutputStream(localPath);
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
encoder.encode(outImg);

out.close();
}
}

------解决方案--------------------
RenderedImage img = ImageIO.read(new File( "a.png "));
ImageIO.write(img, "jpg ", new File( "a.jpg "));
------解决方案--------------------
RenderedImage img = ImageIO.read(new File( "a.png "));
ImageIO.write(img, "jpg ", new File( "a.jpg "));
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轻松的满足了LZ的需求

------解决方案--------------------
楼上正解!这样才是最简单的,com.sun包是低层API,一般情况下不提倡使用这个包.
com.sun.image.codec.jpeg.JPEGCodec;
com.sun.image.codec.jpeg.JPEGImageEncoder;
已经在javax.ImageIO.ImageIO里使用.不用我们操心它们.