Java不需要加载整张图片而获取图片的大小

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();

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.jdk5.images.utils;

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;
	}
}

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package com.jdk5.images.utils;

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;

}

调用方法：

try {
	File f = new File("d:\\image\\org.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());
}

try {

File f = new File("d:\\image\\org.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());

}

输出：

MIME Type : image/jpeg	 Width : 402	 Height : 375
MIME Type : image/jpeg	 Width : 402	 Height : 375
MIME Type : image/jpeg	 Width : 402	 Height : 375

MIME Type : image/jpeg Width : 402 Height : 375

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