怎么把BufferedImage设置背景为透明

近用到Java动态生成背景透明的图片功能，从gif和png中选择了png格式，个中缘由就不说了，于是动手到网上搜索有用的代码。现把搜索结果总结如下： 1. 生成png图片int width = 400;int height = 300;// 创建BufferedImage对象BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);// 获取Graphics2DGraphics2D g2d = image.createGraphics();// 画图g2d.setColor(new Color(255,0,0));g2d.setStroke(new BasicStroke(1));g2d.draw//释放对象g2d.dispose();// 保存文件   ImageIO.write(image, "png", new File("c:/test.png"));int width = 400;int height = 300;// 创建BufferedImage对象BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);// 获取Graphics2DGraphics2D g2d = image.createGraphics();// 画图g2d.setColor(new Color(255,0,0));g2d.setStroke(new BasicStroke(1));g2d.draw//释放对象g2d.dispose();// 保存文件   ImageIO.write(image, "png", new File("c:/test.png"));这只是绘制图形的代码，其背景是黑色的，如何才能背景透明呢？继续搜索，没有得到结果，不过搜出以下代码，它只是把自己绘制的图形设置为透明或半透明，背景并不透明，如下：2. 绘制半透明图形int width = 400;int height = 300;// 创建BufferedImage对象BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);// 获取Graphics2DGraphics2D g2d = image.createGraphics();// 设置透明度g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_ATOP, 1.0f)); // 1.0f为透明度 ，值从0-1.0，依次变得不透明// 画图g2d.setColor(new Color(255,0,0));g2d.setStroke(new BasicStroke(1));g2d.draw//释放对象//透明度设置 结束g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));g2d.dispose();// 保存文件   ImageIO.write(image, "png", new File("c:/test.png"));这样绘制的图形应该说是前景透明的，背景依然是黑色，:(网上没有看到有益的代码，在csdn上一位说自己实现了，但却没有说怎么实现的，没办法只能自己摸索了，耗了半个多小时，几乎查看了BufferedImage 和Graphics2D 所有方法和属性，终于找到了解决方案，只不过是增加两行代码而已，如下：int width = 400;int height = 300;// 创建BufferedImage对象BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);// 获取Graphics2DGraphics2D g2d = image.createGraphics();// ---------- 增加下面的代码使得背景透明 -----------------image = g2d.getDeviceConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);g2d.dispose();g2d = image.createGraphics();// ---------- 背景透明代码结束 -----------------// 画图g2d.setColor(new Color(255,0,0));g2d.setStroke(new BasicStroke(1));g2d.draw//释放对象g2d.dispose();// 保存文件   ImageIO.write(image, "png", new File("c:/test.png"));================================================白背景变透明package com.goldgrid.socket.client;import java.awt.Graphics2D;import java.awt.Image;import java.awt.image.BufferedImage;import java.io.ByteArrayOutputStream;import java.io.File;import javax.imageio.ImageIO;import javax.swing.ImageIcon;import org.apache.log4j.Logger;public class Alpha {    protected static Logger logger = Logger.getLogger(ClientSocket.class);public byte[] transferAlpha(Image image) {   ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();   try {    ImageIcon imageIcon = new ImageIcon(image);    BufferedImage bufferedImage = new BufferedImage(imageIcon      .getIconWidth(), imageIcon.getIconHeight(),      BufferedImage.TYPE_4BYTE_ABGR);    Graphics2D g2D = (Graphics2D) bufferedImage.getGraphics();    g2D.drawImage(imageIcon.getImage(), 0, 0, imageIcon      .getImageObserver());    int alpha = 0;    for (int j1 = bufferedImage.getMinY(); j1 < bufferedImage      .getHeight(); j1++) {     for (int j2 = bufferedImage.getMinX(); j2 < bufferedImage       .getWidth(); j2++) {      int rgb = bufferedImage.getRGB(j2, j1);          int R =(rgb & 0xff0000 ) >> 16 ;      int G= (rgb & 0xff00 ) >> 8 ;      int B= (rgb & 0xff );      if(((255-R)<30) && ((255-G)<30) && ((255-B)<30)){       rgb = ((alpha + 1) << 24) | (rgb & 0x00ffffff);      }      bufferedImage.setRGB(j2, j1, rgb);     }    }    g2D.drawImage(bufferedImage, 0, 0, imageIcon.getImageObserver());    //ImageIO.write(bufferedImage, "png", new File("d:/test.png.png"));    ImageIO.write(bufferedImage, "png", byteArrayOutputStream);   } catch (Exception e) {    logger.error(e.toString());   }finally{      }   return byteArrayOutputStream.toByteArray();}}