java:构建ImageInputStream利用ImageReader对内存字节流进行图像解码

package test;

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Iterator;

import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.stream.ImageInputStream;
import javax.imageio.stream.MemoryCacheImageInputStream;

import org.junit.Test;

public class TestReadMemoryImage {
    @Test
    public final void testreadMemoryImage() throws IllegalArgumentException, IOException {
        // 将图像文件加读取到内存成为字节数组
        byte[] imgBytes = readBytes(TestReadMemoryImage.class.getResourceAsStream("/images/he049.jpg"));
        BufferedImage bufImg = readMemoryImage(imgBytes);
        System.out.printf("decode success,width=%d,heigh=%d\n", bufImg.getWidth(),bufImg.getHeight());
    }
    @Test
    public final void testreadMemoryImage1() throws IllegalArgumentException, IOException {
        // 将图像文件加读取到内存成为字节数组
        byte[] imgBytes = readBytes(TestReadMemoryImage.class.getResourceAsStream("/images/he049.jpg"));
        BufferedImage bufImg = readMemoryImage1(imgBytes);
        System.out.printf("decode success,width=%d,heigh=%d\n", bufImg.getWidth(),bufImg.getHeight());
    }
    /**
     * 从内存字节数组中读取图像
     * 
     * @param imgBytes
     *            未解码的图像数据
     * @return 返回 {@link BufferedImage}
     * @throws IOException
     *             当读写错误或不识别的格式时抛出
     */
    public static final BufferedImage readMemoryImage(byte[] imgBytes) throws IOException {
        if (null == imgBytes || 0 == imgBytes.length)
            throw new NullPointerException("the argument 'imgBytes' must not be null or empty");
        // 将字节数组转为InputStream，再转为MemoryCacheImageInputStream
        ImageInputStream imageInputstream = new MemoryCacheImageInputStream(new ByteArrayInputStream(imgBytes));
        // 获取所有能识别数据流格式的ImageReader对象
        Iterator<ImageReader> it = ImageIO.getImageReaders(imageInputstream);
        // 迭代器遍历尝试用ImageReader对象进行解码
        while (it.hasNext()) {
            ImageReader imageReader = it.next();
            // 设置解码器的输入流
            imageReader.setInput(imageInputstream, true, true);
            // 图像文件格式后缀
            String suffix = imageReader.getFormatName().trim().toLowerCase();
            // 图像宽度
            int width = imageReader.getWidth(0);
            // 图像高度
            int height = imageReader.getHeight(0);
            System.out.printf("format %s,%dx%d\n", suffix, width, height);
            try {
                // 解码成功返回BufferedImage对象
                // 0即为对第0张图像解码(gif格式会有多张图像),前面获取宽度高度的方法中的参数0也是同样的意思
                 return imageReader.read(0, imageReader.getDefaultReadParam());
            } catch (Exception e) {
                imageReader.dispose();
                // 如果解码失败尝试用下一个ImageReader解码
            }
        }
        imageInputstream.close();
        // 没有能识别此数据的图像ImageReader对象，抛出异常
        throw new IOException("unsupported image format");
    }
    public static final BufferedImage readMemoryImage1(byte[] imgBytes) throws IOException {
        if (null == imgBytes || 0 == imgBytes.length)
            throw new NullPointerException("the argument 'imgBytes' must not be null or empty");
        // 将字节数组转为InputStream，再转为MemoryCacheImageInputStream
        ImageInputStream imageInputstream = new MemoryCacheImageInputStream(new ByteArrayInputStream(imgBytes));
        // 直接调用ImageIO.read方法解码
        BufferedImage bufImg = ImageIO.read(imageInputstream);
        if(null==bufImg)
            // 没有能识别此数据的图像ImageReader对象，抛出异常
            throw new IOException("unsupported image format");
        return bufImg;
    }
    /**
     * 从{@link InputStream}读取字节数组<br>
     * 结束时会关闭{@link InputStream}<br>
     * {@code in}为{@code null}时抛出{@link NullPointerException}
     * 
     * @param in
     * @return 字节数组
     * @throws IOException
     */
    public static final byte[] readBytes(InputStream in) throws IOException {
        if (null == in)
            throw new NullPointerException("the argument 'in' must not be null");
        try {
            int buffSize = Math.max(in.available(), 1024 * 8);
            byte[] temp = new byte[buffSize];
            ByteArrayOutputStream out = new ByteArrayOutputStream(buffSize);
            int size = 0;
            while ((size = in.read(temp)) != -1) {
                out.write(temp, 0, size);
            }
            return out.toByteArray();
        } finally {
            in.close();
        }
    }
}