构建保存图片的路径：
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1 String pathdir = "/images/product/"+ productTypeId+ "/"+ productId+ "/prototype";//构建文件保存的目录
为什么要有那么多个目录，因为java本身不会去获取图片，而是调用了操作系统的一些接口来获取图片，如果一个目录下图片太多的话，操作系统获取图片的速度会变慢 ，所以巴巴运动网在构建图片路径的时候搞了多个目录，分散保存图片。
有了这个pathdir就可以得到图片保存目录的真实路径：
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1 String realpathdir = request.getSession().getServletContext().getRealPath(pathdir);
获取了图片的真实路径后，就可以开始保存图片了：
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1 File savedir = new File(realpathdir);
2 File file = saveFile(savedir, filename, imagefile.getFileData());
imagefile为struts的FormFile类的对象，filename为文件名，这两个属性都可以从前台获取过来。以下是saveFile方法的代码：
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1 /**
2 * 保存文件
3 * @param savedir 存放目录
4 * @param fileName 文件名称
5 * @param data 保存的内容
6 * @return 保存的文件
7 * @throws Exception
8 */
9 public static File saveFile(File savedir, String fileName, byte[] data) throws Exception{
10 if(!savedir.exists()) savedir.mkdirs();//如果目录不存在就创建
11 File file = new File(savedir, fileName);
12 FileOutputStream fileoutstream = new FileOutputStream(file);
13 fileoutstream.write(data);
14 fileoutstream.close();
15 return file;
16 }
保存完图片后还要保存一张图片的缩略图，宽度为140px
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1 String pathdir140 = "/images/product/"+ productTypeId+ "/"+ productId+ "/140x";//140宽度的图片保存目录
2 String realpathdir140 = request.getSession().getServletContext().getRealPath(pathdir140);
3 File savedir140 = new File(realpathdir140);
4 if(!savedir140.exists()) savedir140.mkdirs();//如果目录不存在就创建
5 File file140 = new File(realpathdir140, filename);
6 ImageSizer.resize(file, file140, 140, ext);
这里我们用到了一个从网上下的用于压缩图片的ImageSizer工具类的静态方法，resize方法传进去的四个参数分别代表原始图片对象，需要被压缩的图片对象，压缩宽度的大小，图片后缀名。这个工具类只能压缩jpg, png, gif(非动画)三种格式，如果想压缩更多的格式需要付费。以下是该工具类：
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1 /**
2 * 图像压缩工具
3 * @author lihuoming@sohu.com
4 *
5 */
6 public class ImageSizer {
7 public static final MediaTracker tracker = new MediaTracker(new Component() {
8 private static final long serialVersionUID = 1234162663955668507L;}
9 );
10 /**
11 * @param originalFile 原图像
12 * @param resizedFile 压缩后的图像
13 * @param width 图像宽
14 * @param format 图片格式 jpg, png, gif(非动画)
15 * @throws IOException
16 */
17 public static void resize(File originalFile, File resizedFile, int width, String format) throws IOException {
18 if(format!=null && "gif".equals(format.toLowerCase())){
19 resize(originalFile, resizedFile, width, 1);
20 return;
21 }
22 FileInputStream fis = new FileInputStream(originalFile);
23 ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
24 int readLength = -1;
25 int bufferSize = 1024;
26 byte bytes[] = new byte[bufferSize];
27 while ((readLength = fis.read(bytes, 0, bufferSize)) != -1) {
28 byteStream.write(bytes, 0, readLength);
29 }
30 byte[] in = byteStream.toByteArray();
31 fis.close();
32 byteStream.close();
33
34 Image inputImage = Toolkit.getDefaultToolkit().createImage( in );
35 waitForImage( inputImage );
36 int imageWidth = inputImage.getWidth( null );
37 if ( imageWidth < 1 )
38 throw new IllegalArgumentException( "image width " + imageWidth + " is out of range" );
39 int imageHeight = inputImage.getHeight( null );
40 if ( imageHeight < 1 )
41 throw new IllegalArgumentException( "image height " + imageHeight + " is out of range" );
42
43 // Create output image.
44 int height = -1;
45 double scaleW = (double) imageWidth / (double) width;
46 double scaleY = (double) imageHeight / (double) height;
47 if (scaleW >= 0 && scaleY >=0) {
48 if (scaleW > scaleY) {
49 height = -1;
50 } else {
51 width = -1;
52 }
53 }
54 Image outputImage = inputImage.getScaledInstance( width, height, java.awt.Image.SCALE_DEFAULT);
55 checkImage( outputImage );
56 encode(new FileOutputStream(resizedFile), outputImage, format);
57 }
58
59 /** Checks the given image for valid width and height. */
60 private static void checkImage( Image image ) {
61 waitForImage( image );
62 int imageWidth = image.getWidth( null );
63 if ( imageWidth < 1 )
64 throw new IllegalArgumentException( "image width " + imageWidth + " is out of range" );
65 int imageHeight = image.getHeight( null );
66 if ( imageHeight < 1 )
67 throw new IllegalArgumentException( "image height " + imageHeight + " is out of range" );
68 }
69
70 /** Waits for given image to load. Use before querying image height/width/colors. */
71 private static void waitForImage( Image image ) {
72 try {
73 tracker.addImage( image, 0 );
74 tracker.waitForID( 0 );
75 tracker.removeImage(image, 0);
76 } catch( InterruptedException e ) { e.printStackTrace(); }
77 }
78
79 /** Encodes the given image at the given quality to the output stream. */
80 private static void encode( OutputStream outputStream, Image outputImage, String format )
81 throws java.io.IOException {
82 int outputWidth = outputImage.getWidth( null );
83 if ( outputWidth < 1 )
84 throw new IllegalArgumentException( "output image width " + outputWidth + " is out of range" );
85 int outputHeight = outputImage.getHeight( null );
86 if ( outputHeight < 1 )
87 throw new IllegalArgumentException( "output image height " + outputHeight + " is out of range" );
88
89 // Get a buffered image from the image.
90 BufferedImage bi = new BufferedImage( outputWidth, outputHeight,
91 BufferedImage.TYPE_INT_RGB );
92 Graphics2D biContext = bi.createGraphics();
93 biContext.drawImage( outputImage, 0, 0, null );
94 ImageIO.write(bi, format, outputStream);
95 outputStream.flush();
96 }
97
98 /**
99 * 缩放gif图片
100 * @param originalFile 原图片
101 * @param resizedFile 缩放后的图片
102 * @param newWidth 宽度
103 * @param quality 缩放比例 (等比例)
104 * @throws IOException
105 */
106 private static void resize(File originalFile, File resizedFile, int newWidth, float quality) throws IOException {
107 if (quality < 0 || quality > 1) {
108 throw new IllegalArgumentException("Quality has to be between 0 and 1");
109 }
110 ImageIcon ii = new ImageIcon(originalFile.getCanonicalPath());
111 Image i = ii.getImage();
112 Image resizedImage = null;
113 int iWidth = i.getWidth(null);
114 int iHeight = i.getHeight(null);
115 if (iWidth > iHeight) {
116 resizedImage = i.getScaledInstance(newWidth, (newWidth * iHeight) / iWidth, Image.SCALE_SMOOTH);
117 } else {
118 resizedImage = i.getScaledInstance((newWidth * iWidth) / iHeight, newWidth, Image.SCALE_SMOOTH);
119 }
120 // This code ensures that all the pixels in the image are loaded.
121 Image temp = new ImageIcon(resizedImage).getImage();
122 // Create the buffered image.
123 BufferedImage bufferedImage = new BufferedImage(temp.getWidth(null), temp.getHeight(null),
124 BufferedImage.TYPE_INT_RGB);
125 // Copy image to buffered image.
126 Graphics g = bufferedImage.createGraphics();
127 // Clear background and paint the image.
128 g.setColor(Color.white);
129 g.fillRect(0, 0, temp.getWidth(null), temp.getHeight(null));
130 g.drawImage(temp, 0, 0, null);
131 g.dispose();
132 // Soften.
133 float softenFactor = 0.05f;
134 float[] softenArray = {0, softenFactor, 0, softenFactor, 1-(softenFactor*4), softenFactor, 0, softenFactor, 0};
135 Kernel kernel = new Kernel(3, 3, softenArray);
136 ConvolveOp cOp = new ConvolveOp(kernel, ConvolveOp.EDGE_NO_OP, null);
137 bufferedImage = cOp.filter(bufferedImage, null);
138 // Write the jpeg to a file.
139 FileOutputStream out = new FileOutputStream(resizedFile);
140 // Encodes image as a JPEG data stream
141 JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
142 JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(bufferedImage);
143 param.setQuality(quality, true);
144 encoder.setJPEGEncodeParam(param);
145 encoder.encode(bufferedImage);
146 }
147 }
允许用户上传文件，那么我们一定要注意安全，如果用户上传了一个jsp文件，而这个文件的上传路径恰好能被用户访问到，那么用户可能会在这个jsp文件里面做一个对网站其他文件的文件操作，可以将文件保存到web-inf下面，如果用户需要下载，我们就写一个servlet读取这个文件，以流的方式返回给用户。