Question

在使用JSF和JPA的java ee应用程序中，我必须计算对象列表中的属性总数。我使用LambdaJ库来实现总和的计算。

由于我在应用程序的几个地方使用这种总结并可能对整体性能产生影响，因此我设计了以下测试java应用程序来测试LambdaJ的功效。

该申请表明LambdaJ的功效严重不足。

测试程序中是否有任何错误，或者我应该用迭代替换所有lambdaJ事件？

结果

Time taken to calculate a single total by iteration is 15 milliseconds.
Time taken to calculate a single total by LambdaJ is 199 milliseconds.
Time taken to calculate multiple totals by iteration is 23 milliseconds.
Time taken to calculate multiple totals by LambdaJ is 114 milliseconds.

主要方法

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.lakmedi;

import ch.lambdaj.Lambda;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Random;

/**
 *
 * @author buddhika
 */
public class main {

    public static void main(String[] args) {
        List<Bill> bills = new ArrayList<>();
        Random r = new Random();
        for (int i = 0; i < 100000; i++) {
            Bill b = new Bill();
            b.setGrossTotal(r.nextDouble());
            b.setDiscount(r.nextDouble());
            b.setNetTotal(b.getGrossTotal() - b.getDiscount());
            bills.add(b);
        }
        calSingleByIteration(bills);
        calSingleByLambdja(bills);
        calMultipleByIteration(bills);
        calMultipleByLambdja(bills);
    }

    public static void calSingleByIteration(List<Bill> bills) {
        Date startTime = new Date();
        double grossTotal = 0.0;
        for (Bill b : bills) {
            grossTotal += b.getGrossTotal();
        }
        Date endTime = new Date();
        long timeTaken = endTime.getTime() - startTime.getTime();
        System.out.println("Time taken to calculate a single total by iteration is " + timeTaken + " milliseconds.");
    }

    public static void calSingleByLambdja(List<Bill> bills) {
        Date startTime = new Date();
        double grossTotal = Lambda.sumFrom(bills).getGrossTotal();
        Date endTime = new Date();
        long timeTaken = endTime.getTime() - startTime.getTime();
        System.out.println("Time taken to calculate a single total by LambdaJ is " + timeTaken + " milliseconds.");
    }

    public static void calMultipleByIteration(List<Bill> bills) {
        Date startTime = new Date();
        double grossTotal = 0.0;
        double discount = 0.0;
        double netTotal = 0.0;
        for (Bill b : bills) {
            grossTotal += b.getGrossTotal();
            discount += b.getDiscount();
            netTotal += b.getNetTotal();
        }
        Date endTime = new Date();
        long timeTaken = endTime.getTime() - startTime.getTime();
        System.out.println("Time taken to calculate multiple totals by iteration is " + timeTaken + " milliseconds.");
    }

    public static void calMultipleByLambdja(List<Bill> bills) {
        Date startTime = new Date();
        double grossTotal = Lambda.sumFrom(bills).getGrossTotal();
        double discount = Lambda.sumFrom(bills).getDiscount();
        double netTotal = Lambda.sumFrom(bills).getNetTotal();
        Date endTime = new Date();
        long timeTaken = endTime.getTime() - startTime.getTime();
        System.out.println("Time taken to calculate multiple totals by LambdaJ is " + timeTaken + " milliseconds.");
    }

}

比尔等级

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package com.lakmedi;

/**
 *
 * @author buddhika
 */
public class Bill {
    private double grossTotal;
    private double netTotal;
    private double discount;

    public double getGrossTotal() {
        return grossTotal;
    }

    public void setGrossTotal(double grossTotal) {
        this.grossTotal = grossTotal;
    }

    public double getNetTotal() {
        return netTotal;
    }

    public void setNetTotal(double netTotal) {
        this.netTotal = netTotal;
    }

    public double getDiscount() {
        return discount;
    }

    public void setDiscount(double discount) {
        this.discount = discount;
    }


}

Answer 1

假设您的意思是efficiency而不是efficacy，那么您的衡量表现或多或少与预期一致 - 请参阅LambdaJ自己的performance analysis。

使用Java 8 Lambda Expressions可能会获得更好的结果，但这里的主要目标是提高源代码的可读性和可维护性，而不是提高速度。您确定执行汇总所需的时间对于应用程序的整体性能至关重要吗？我怀疑考虑（I / O）HTTP流量（JSF）和数据库查询（JPA）的等待时间，在这种情况下，这是premature optimization（所有邪恶的根源）。

Answer 2

首先，检查您使用的是最新版本的LambdaJ，因为project site表示最新版本有一些性能改进。

但是，我认为你应该期望lambdaj比写同等的for-loop慢。在更简洁的语法背后，JVM正在做更多的工作。

您可以考虑删除lambdaj并使用Java 8流和lambda表达式。

以下是lambdaj的作者对此事所说的话：

Lemme再次澄清一下：在Java8发布之后，我没有看到开发/维护#lambdaj的任何意义。转到Java8＆amp;快乐

- Mario Fusco, May 2014

使用LambdaJ超过迭代的总效率不足

2 个答案: