Java不需要加载整张图片而获取图片的大小

转载地址 http://blog.jdk5.com/zh/java-get-image-size-without-loading-the-whole-data/
利用Java类，获取图片的类型，宽度和高度，方法有多种，比如：

BufferedImage bimg = ImageIO.read(new File("d:\\image\\org.jpg"));
int width = bimg.getWidth();
int height = bimg.getHeight();

但这方法将整张图片都加载到了内存，如果那些图片比较大，无疑将增加服务的压力。

下面推荐一个更简单的方法，不需要加载整个图片，从而节省内存空间。

代码如下：

package com.jiafuwei.java;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class SimpleImageInfo {
private int height;
private int width;
private String mimeType;

public SimpleImageInfo(File file) throws IOException {
InputStream is = new FileInputStream(file);
try {
processStream(is);
} finally {
is.close();
}
}

public SimpleImageInfo(InputStream is) throws IOException {
processStream(is);
}

public SimpleImageInfo(byte[] bytes) throws IOException {
InputStream is = new ByteArrayInputStream(bytes);
try {
processStream(is);
} finally {
is.close();
}
}

private void processStream(InputStream is) throws IOException {
int c1 = is.read();
int c2 = is.read();
int c3 = is.read();

mimeType = null;
width = height = -1;

if (c1 == 'G' && c2 == 'I' && c3 == 'F') { // GIF
is.skip(3);
width = readInt(is,2,false);
height = readInt(is,2,false);
mimeType = "image/gif";
} else if (c1 == 0xFF && c2 == 0xD8) { // JPG
while (c3 == 255) {
int marker = is.read();
int len = readInt(is,2,true);
if (marker == 192 || marker == 193 || marker == 194) {
is.skip(1);
height = readInt(is,2,true);
width = readInt(is,2,true);
mimeType = "image/jpeg";
break;
}
is.skip(len - 2);
c3 = is.read();
}
} else if (c1 == 137 && c2 == 80 && c3 == 78) { // PNG
is.skip(15);
width = readInt(is,2,true);
is.skip(2);
height = readInt(is,2,true);
mimeType = "image/png";
} else if (c1 == 66 && c2 == 77) { // BMP
is.skip(15);
width = readInt(is,2,false);
is.skip(2);
height = readInt(is,2,false);
mimeType = "image/bmp";
} else {
int c4 = is.read();
if ((c1 == 'M' && c2 == 'M' && c3 == 0 && c4 == 42)
|| (c1 == 'I' && c2 == 'I' && c3 == 42 && c4 == 0)) { //TIFF
boolean bigEndian = c1 == 'M';
int ifd = 0;
int entries;
ifd = readInt(is,4,bigEndian);
is.skip(ifd - 8);
entries = readInt(is,2,bigEndian);
for (int i = 1; i <= entries; i++) {
int tag = readInt(is,2,bigEndian);
int fieldType = readInt(is,2,bigEndian);
int valOffset;
if ((fieldType == 3 || fieldType == 8)) {
valOffset = readInt(is,2,bigEndian);
is.skip(2);
} else {
valOffset = readInt(is,4,bigEndian);
}
if (tag == 256) {
width = valOffset;
} else if (tag == 257) {
height = valOffset;
}
if (width != -1 && height != -1) {
mimeType = "image/tiff";
break;
}
}
}
}
if (mimeType == null) {
throw new IOException("Unsupported image type");
}
}

private int readInt(InputStream is, int noOfBytes, boolean bigEndian) throws IOException {
int ret = 0;
int sv = bigEndian ? ((noOfBytes - 1) * 8) : 0;
int cnt = bigEndian ? -8 : 8;
for(int i=0;i<noOfBytes;i++) {
ret |= is.read() << sv;
sv += cnt;
}
return ret;
}

public int getHeight() {
return height;
}

public void setHeight(int height) {
this.height = height;
}

public int getWidth() {
return width;
}

public void setWidth(int width) {
this.width = width;
}

public String getMimeType() {
return mimeType;
}

public void setMimeType(String mimeType) {
this.mimeType = mimeType;
}

@Override
public String toString() {
return "MIME Type : " + mimeType + "\t Width : " + width
+ "\t Height : " + height;
}
}

package com.jiafuwei.java;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;

public class Test {
public static void main(String[] args) {
try {
File f = new File("E:\\1.jpg");
// Getting image data from a InputStream
FileInputStream b = new FileInputStream(f);
SimpleImageInfo imageInfo = new SimpleImageInfo(b);
System.out.println(imageInfo);
// Getting image data from a file
imageInfo = new SimpleImageInfo(f);
System.out.println(imageInfo);
// Getting image data from a byte array
byte[] buffer = new byte[1024 * 6];
InputStream is = new FileInputStream(f);
while (is.read(buffer) == -1) {}
is.close();
imageInfo = new SimpleImageInfo(buffer);
System.out.println(imageInfo);
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
}