java - java-GroupBy框架

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在Java中，我正在寻找一个基于类的某些属性执行POJO分组的框架。

例如：简单的例子

Salary {
int userId;
Double salary;
String office;
}

汇总1：在办公室获得平均薪水。

汇总2：所有薪金总和

汇总3：按办公室划分的薪金总和

最佳答案

您可以使用http://code.google.com/p/lambdaj/

关于兰伯达（Lambdaj）：

lambdaj旨在轻松操纵集合。其功能旨在过滤，转换，索引和聚合集合的项目，而无需对其进行显式迭代。

举个例子;

Salary.java

package x;

public class Salary {
    int userId;
    Double salary;
    String office;
    public Salary(int userId, Double salary, String office) {
        super();
        this.userId = userId;
        this.salary = salary;
        this.office = office;
    }
    public int getUserId() {
        return userId;
    }
    public void setUserId(int userId) {
        this.userId = userId;
    }
    public Double getSalary() {
        return salary;
    }
    public void setSalary(Double salary) {
        this.salary = salary;
    }
    public String getOffice() {
        return office;
    }
    public void setOffice(String office) {
        this.office = office;
    }


}

LambdaX.java

package x;

import java.util.ArrayList;
import java.util.List;

import org.hamcrest.Matchers;

import static ch.lambdaj.Lambda.*;

public class LambdajX {

    public static void main(String[] args) {
        List<Salary> salaries = new ArrayList<Salary>();
        salaries.add(new Salary(1, 100.0, "mexico"));
        salaries.add(new Salary(2, 130.0, "germany"));
        salaries.add(new Salary(3, 190.0, "mexico"));

        LambdajX lambdajX = new LambdajX();

        System.out.println("Total Salary : "
                + lambdajX.getAggregateSalary(salaries));
        System.out.println("Total Salary in Mexico : "
                + lambdajX.getAggregateSalaryByOffice(salaries, "mexico"));

        System.out.println("Avg Salary : "
                + lambdajX.getAverageSalary(salaries));

        System.out.println("Avg Salary in Mexico :"
                + lambdajX.getAverageSalaryByOffice(salaries, "mexico"));

    }

    public Double getAggregateSalary(List<Salary> salaries) {
        return sum(salaries, on(Salary.class).getSalary());
    }

    public Double getAggregateSalaryByOffice(List<Salary> salaries,
            String office) {

        return sumFrom(
                select(salaries,
                        having(on(Salary.class).getOffice(),
                                Matchers.equalTo(office)))).getSalary();

    }

    public Double getAverageSalary(List<Salary> salaries) {
        return avg(salaries, on(Salary.class).getSalary());
    }

    public Double getAverageSalaryByOffice(List<Salary> salaries, String office) {

        return avgFrom(
                select(salaries,
                        having(on(Salary.class).getOffice(),
                                Matchers.equalTo("mexico")))).getSalary();

    }
}

使用的库：lambdaj-2.4-with-dependencies.jar

您可以从http://lambdaj.googlecode.com/files/lambdaj-2.4-with-dependencies.jar下载此jar文件

另一种选择是谷歌的番石榴。