IO密集型是指对IO操作较多的任务。下面以查询一些股票价格任务为例：
YahooFinance.java
public class YahooFinance {public static double getPrice(final String ticker) throws IOException{final URL url = new URL("http://ichart./table.csv?s=" + ticker);final BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));String discardHeader = reader.readLine();System.out.println(discardHeader);String data = reader.readLine();//Sample of data://Date,Open,High,Low,Close,Volume,Adj Close//-09-05,9.08,9.12,8.98,9.02,16212600,9.02//System.out.println(data);String[] dataItems = data.split(",");double price = Double.valueOf(dataItems[dataItems.length - 1]);return price;}public static void main(String[] args) throws IOException{YahooFinance.getPrice("600401.SS");}}
AbstractCalTotal.java 顺序查询和多线程查询的基类
public abstract class AbstractCalTotal {private static String[] stockArr = {"600401.SS,100", "600120.SS,200", "600728.SS,300", "600268.SS,400", "601258.SS,500",//"AMGN,100", "AMZN,200", "BAC,300", "AAPL,400", "HYGF,500",//"ZHFJ,100", "dlkg,200", "BMY,300", "KDXF,400", "CWSZ,500",//"FZDJ,100", "GDNZ,200", "htdl,300", "zsyh,400", "JLQC,500",//"JMGF,100", "PDJT,200", "GLM,300", "ZGQY,400", "hyjx,500", };//股票代码.上交所（深交所）,股票数量public static Map<String, Integer> readTickers() throws IOException{Map<String, Integer> stocks = new HashMap<>();String[] info = null;for(int i = 0 ; i < stockArr.length; i++){info = stockArr[i].split(",");stocks.put(info[0], Integer.valueOf(info[1]));}return stocks;}public void timeAndComputeValue() throws ExecutionException, InterruptedException, IOException{long start = System.nanoTime();Map<String, Integer> stocks = readTickers();double nav = computeNetAssetValue(stocks);long end = System.nanoTime();String value = new DecimalFormat("$##,##0.00").format(nav);System.out.println("Total net asset value: " + value);System.out.println("Time (seconds) taken: " + (end - start)/1.0e9);}public abstract double computeNetAssetValue(Map<String, Integer> stocks) throws ExecutionException, InterruptedException, IOException;}
顺序查询
public class SequentialCal extends AbstractCalTotal{@Overridepublic double computeNetAssetValue(Map<String, Integer> stocks)throws IOException {double values = 0.0;for(String ticker : stocks.keySet()){values += stocks.get(ticker)* YahooFinance.getPrice(ticker);}return values;}public static void main(String[] args)throws ExecutionException, InterruptedException, IOException{new SequentialCal().timeAndComputeValue();}}
多线程查询
//调整 blockingCoefficient，可找出较少的执行时间public class ConcurrentCal extends AbstractCalTotal{public double computeNetAssetValue(final Map<String, Integer> stocks)throws ExecutionException, InterruptedException, IOException {int numberOfCores = Runtime.getRuntime().availableProcessors();double blockingCoefficient = 0.9;final int poolSize = (int)(numberOfCores / (1 - blockingCoefficient));System.out.println("Pool size is: " + poolSize);List<Callable<Double>> partitions = new ArrayList<>();for(final String ticker : stocks.keySet()){partitions.add(new Callable<Double>(){public Double call() throws Exception{return stocks.get(ticker) * YahooFinance.getPrice(ticker);}});}final ExecutorService executorPool = Executors.newFixedThreadPool(poolSize);final List<Future<Double>> valueOfStocks = executorPool.invokeAll(partitions, 100, TimeUnit.SECONDS);double netAssetValue = 0.0;//每次循环只能取到一个子任务的结果，且子任务的顺序与我们创建的顺序是一致的。for(final Future<Double> vas : valueOfStocks){netAssetValue += vas.get(); //vas.get() 如果此任务尚未完成，程序会等待 }executorPool.shutdown();return netAssetValue;}public static void main(String[] args)throws ExecutionException, InterruptedException, IOException{new ConcurrentCal().timeAndComputeValue();}}
