需求:利用Fork/Join框架来统计某个字符串在某个文件夹的文件中出现的次数。主要用到的技术点:JDK8的Stream、Lambda表达式、Fork/Join框架.
如果对于Fork/Join不了解的话可以参考这里:http://www.infoq.com/cn/articles/fork-join-introduction、http://ifeve.com/fork-join-1/、http://www.iteye.com/topic/643724。主要代码如下:
package com.zkn.fullstacktraining.seventh;
import com.google.common.collect.Lists;
import javafx.util.Pair;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
/**
* Created by wb-zhangkenan on 2017/2/6.
* 通过Fork/Join的方式来统计某个字符串在某个文件夹下的文件中出现的次数
*/
public class SearchStringByForkJoin extends RecursiveTask<List<Pair<String, Integer>>> {
//任务的阀值
private static final int THRESHOLD = 5;
//任务区间的开始值
private int start;
//任务区间的结束值
private int end;
//所有的路径信息
private List<Path> allPaths;
public SearchStringByForkJoin(int start, int end, List<Path> allPaths) {
this.start = start;
this.end = end;
this.allPaths = allPaths;
}
public static void main(String[] args) {
ForkJoinPool forkJoinPool = new ForkJoinPool();
try {
List<Path> pathList = Files.walk(Paths.get("D:\\CUST\\WORK\\Exercises\\FullStackTraining\\src\\main\\java\\com\\zkn"), 4)
.filter(file -> !Files.isDirectory(file) && file.toString().endsWith("java"))
.collect(Collectors.toList());
SearchStringByForkJoin searchStringByForkJoin = new SearchStringByForkJoin(0, pathList.size(), pathList);
Future<List<Pair<String, Integer>>> result =
forkJoinPool.submit(searchStringByForkJoin);
List<Pair<String, Integer>> pairList = result.get();
pairList.stream()
.filter(pair -> pair.getValue() > 0)
.sorted((s1, s2) -> Integer.compare(s2.getValue(), s1.getValue()))
.forEach(pair -> System.out.println(String.format("%d次出现在%s文件中", pair.getValue(), pair.getKey().toString())));
forkJoinPool.shutdown();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
/**
* The main computation performed by this task.
* @return the result of the computation
*/
@Override
protected List<Pair<String, Integer>> compute() {
List<Pair<String, Integer>> pairList = Lists.newArrayList();
boolean canCompute = end - start <= THRESHOLD;
if (canCompute) {
pairList = IntStream.range(start, end + 1).mapToObj(i -> {
//到集合的结尾了
if (i == allPaths.size())
return new Pair<>("", 0);
int sum = 0;
try {
Optional optional = Files.lines(allPaths.get(i)).map(file -> {
int count = 0;
int flag = file.indexOf("main");
if (flag >= 0) {
do {
count++;
} while ((flag = file.indexOf("main", flag + 1)) > 0);
}
return count;
}).reduce(Integer::sum);
sum = optional.isPresent() ? (int) optional.get() : 0;
} catch (IOException e) {
e.printStackTrace();
}
return new Pair<>(allPaths.get(i).toString(), sum);
}).collect(Collectors.toList());
} else {
//取中间值
int middle = (end + start) / 2;
//创建Fork子任务
SearchStringByForkJoin leftFork = new SearchStringByForkJoin(start, middle, allPaths);
//创建Fork子任务
SearchStringByForkJoin rightFork = new SearchStringByForkJoin(middle + 1, end, allPaths);
//执行子任务
leftFork.fork();
rightFork.fork();
//合并子任务的结果集
pairList.addAll(leftFork.join());
pairList.addAll(rightFork.join());
}
return pairList;
}
}
时间: 2024-09-29 19:27:03