【高效获取jpeg图片的尺寸】
获取图片的尺寸有三种方法：
1.将整个图片文件加载成 BufferedImage 后获取其尺寸；
2.用 ImageReader 快捷获取
3.即windows xp sp3纯净安装版xp系统下载下文所陈述的方式
做过简陋的测试，效率自 1 至 3 逐步递增。
ImageInfo.java
/**
* @author kodeyang
*/
public class ImageInfo {
private int height;
private int width;
public ImageInfo(int height, int width) {
super();
this.height = height;
this.width = width;
}
public int getWidth() {
return width;
}
public int getHeight() {
return height;
}
@Override
public String toString() {
return "height: " + height + ", width: " + width;
}
}
import java.io.IOException;
import java.io.InputStream;
/**
* @author yang3wei
*
*/
public class JpegInfoReader {
private static final byte TAG_START = (byte) 0xff;
private static final byte START_OF_IMAGE = (byte) 0xd8;
private static final byte END_OF_IMAGE = (byte) 0xd9;
private static final byte START_OF_FRAME = (byte) 0xc0;
private static final byte RESTART_MODULO_START = (byte) 0xd0;
private static final byte RESTART_MODULO_END = (byte) 0xd7;
private static final byte START_OF_SCAN = (byte) 0xda;
public static ImageInfo getImageInfo(InputStream in) throws IOException {
// 0-1: store JPEG tag
// 2-3: store JPEG tag length
// 4-5: store JPEG image height
// 6-7: store JPEG image width
byte[] seg = new byte[8];
// read JPEG START_OF_IMAGE tag
if (in.read(seg, 0, 2) == -1) {
return null;
}
// if the first two bytes is not 0xff, 0xd8,
// that is the image format is not JPEG
if (seg[0] != TAG_START || seg[1] != START_OF_IMAGE) {
return null;
}
while (true) {
// read JPEG data tag, offset 0 must be 0xff
if (in.read(seg, 0, 2) == -1) {
return null;
}
// if tag does not start with 0xff,
// the image format is not JPEG
if (seg[0] != TAG_START) {
return null;
}
// Ignore JPEG RESTART_MODULO tag
if (seg[1] >= RESTART_MODULO_START && seg[1] <= RESTART_MODULO_END) {
continue;
}
// find JPEG format START_OF_SCAN part,
// data that starts with poisition is JPEG compression image data,
// that never contains image meta information
if (seg[1] == START_OF_SCAN) {
return null;
}
// find JPEG format END_OF_IMAGE tag, finish scan
if (seg[1] == END_OF_IMAGE) {
return null;
}
// read JPEG data tag length
if (in.read(seg, 2, 2) == -1) {
return null;
}
// find START_OF_FRAME tag
if (seg[1] == START_OF_FRAME) {
break;
}
// skip JPEG data segement
byte[] skip = new byte[toInt(seg, 2) - 2];
if (in.read(skip) == -1) {
return null;
}
}
