java 7 fork/join模糊图像示例， java 8 lambda 并行聚合函数 parallelSort()

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fork/join 线程模型被用来实现了java.util.Arrays 的 parallelSort() ，该方法功能类似sort().

java 8 的java.util.streams 包里的聚合操作的并行方法都是用它来实现的，如

parallelStream()

思路：

if (我的工作是小于一个阀值的)  直接做我的工作else  把我的工作分解成两部分  调用这两个部分并等待它们返回结果

这是如下标红字体所实现的思路，也是核心

调用它

ForkBlur fb = new ForkBlur(src, 0, src.length, dst);ForkJoinPool pool = new ForkJoinPool();pool.invoke(fb);

以下代码是把一张图片弄浑浊。总的思路：

划定算平均值的范围，一个像素点用它周围的每个点的红，绿，蓝的平均值来代替

具体注释如下

import java.awt.image.BufferedImage;import java.io.File;import java.util.concurrent.ForkJoinPool;import java.util.concurrent.RecursiveAction;import javax.imageio.ImageIO;public class ForkBlur extends RecursiveAction {private int[] mSource;private int mStart;private int mLength;private int[] mDestination;// Processing window size; should be odd.划定算平均值的范围private int mBlurWidth = 3;public ForkBlur(int[] src, int start, int length, int[] dst) {mSource = src;mStart = start;mLength = length;mDestination = dst;}protected void computeDirectly() {int sidePixels = (mBlurWidth - 1) / 2;for (int index = mStart; index < mStart + mLength; index++) {// Calculate average.一个像素点用它周围的每个点的红，绿，蓝的平均值来代替float rt = 0, gt = 0, bt = 0;for (int mi = -sidePixels; mi <= sidePixels; mi++) {int mindex = Math.min(Math.max(mi + index, 0), mSource.length - 1);//在选取的范围之内，但不能超过总的边界int pixel = mSource[mindex];rt += (float) ((pixel & 0x00ff0000) >> 16) / mBlurWidth;//红色是ff所在的那些位gt += (float) ((pixel & 0x0000ff00) >> 8) / mBlurWidth;bt += (float) ((pixel & 0x000000ff) >> 0) / mBlurWidth;}// Reassemble destination pixel.int dpixel = (0xff000000) | (((int) rt) << 16) | (((int) gt) << 8) | (((int) bt) << 0);mDestination[index] = dpixel;}}protected static int sThreshold = 100000;protected void compute() {//不是显示调用，是java虚拟机自动调用        if (mLength < sThreshold) {            computeDirectly();            return;        }        int split = mLength / 2;        invokeAll(new ForkBlur(mSource, mStart, split, mDestination),                new ForkBlur(mSource, mStart + split, mLength - split, mDestination));//是一个递归调用}// Plumbing follows.public static void main(String[] args) throws Exception {       String srcName = "red-tulips.jpg";        File srcFile = new File(srcName);       BufferedImage image = ImageIO.read(srcFile);     System.out.println("Source image: " + srcName);     BufferedImage blurredImage = blur(image);    String dstName = "blurred-tulips.jpg";    File dstFile = new File(dstName);    ImageIO.write(blurredImage, "jpg", dstFile);    System.out.println("Output image: " + dstName);}public static BufferedImage blur(BufferedImage srcImage) {int w = srcImage.getWidth();int h = srcImage.getHeight();int[] src = srcImage.getRGB(0, 0, w, h, null, 0, w);int[] dst = new int[src.length];System.out.println("Array size is " + src.length);System.out.println("Threshold is " + sThreshold);int processors = Runtime.getRuntime().availableProcessors();System.out.println(Integer.toString(processors) + " processor" + (processors != 1 ? "s are " : " is ") + "available");ForkBlur fb = new ForkBlur(src, 0, src.length, dst);ForkJoinPool pool = new ForkJoinPool();long startTime = System.currentTimeMillis();pool.invoke(fb);long endTime = System.currentTimeMillis();System.out.println("Image blur took " + (endTime - startTime) + " milliseconds.");BufferedImage dstImage = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);dstImage.setRGB(0, 0, w, h, dst, 0, w);return dstImage;}}

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