Java Stream How to - Process Stream in Parallel

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Question

We would like to know how to process Stream in Parallel.

Answer

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
/*  ww w . jav a2 s .  co m*/
public class Main {
  public static void main(String[] args) {
    List<Trade> trades = TradeUtil.createTrades(100);

    int cpus = Runtime.getRuntime().availableProcessors();
    long start = System.currentTimeMillis();
    trades.stream().parallel().forEach(t -> doSomething(t));
    long end = System.currentTimeMillis();

    System.out.println("Time for parallel op:" + (end - start) / 1000
        + "sec on " + cpus);
  }

  private static void doSomething(Trade t) {
    try {
      System.out.println(t);
      TimeUnit.SECONDS.sleep(2);
    } catch (InterruptedException ex) {
      System.out.println("Sleeping...");
    }
  }
}

class TradeUtil {

  public static List<Trade> createTrades() {
    List<Trade> trades = new ArrayList<Trade>();

    Trade t = new Trade(1, "IBM", 1000, "NEW");
    trades.add(t);
    t = new Trade(2, "APPL", 2000, "NEW");
    trades.add(t);
    t = new Trade(3, "IBM", 3000, "NEW");
    trades.add(t);
    t = new Trade(4, "IBM", 4000, "PENDING");
    trades.add(t);

    return trades;
  }

  public static List<Trade> createTrades(int size) {
    List<Trade> trades = new ArrayList<>();

    for (int i = 0; i < size; i++) {
      Trade t = new Trade(i, "ISUER " + i, i + 1000, "NEW");
      trades.add(t);
    }

    return trades;
  }

}

class Trade {

  private int tradeId = 0;
  private String issuer = null;
  private int quantity = 0;
  private String status = null;

  public Trade(int id, String issuer, int quantity, String status) {
    this.tradeId = id;
    this.issuer = issuer;
    this.quantity = quantity;
    this.status = status;
  }

  public int getTradeId() {
    return tradeId;
  }

  public void setTradeId(int tradeId) {
    this.tradeId = tradeId;
  }

  public String getIssuer() {
    return issuer;
  }

  public void setIssuer(String issuer) {
    this.issuer = issuer;
  }

  public int getQuantity() {
    return quantity;
  }

  public void setQuantity(int quantity) {
    this.quantity = quantity;
  }

  public String getStatus() {
    return status;
  }

  public void setStatus(String status) {
    this.status = status;
  }

  @Override
  public String toString() {
    return "Trade{" + "tradeId=" + tradeId + ", issuer=" + issuer
        + ", quantity=" + quantity + ", status=" + status + '}';
  }

}

The code above generates the following result.

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