全面解析 Java Comparator：一步步掌握排序技巧！-51CTO.COM

排序是编程中最基础且常见的需求之一。在 Java 中，Comparator 接口是实现定制化排序的强大工具。本文将通过代码示例深入讲解 Comparator 的用法，并结合一个实际的 Spring Boot 项目展示如何在前后端实现排序功能。

Comparator 接口详细介绍

Comparator 是 Java 中用于定义对象排序规则的接口。它位于 java.util 包中，常用于对集合或数组中的对象进行排序。与 Comparable 接口相比，Comparator 更灵活，它允许我们为不同的排序需求定义多个比较器。

核心方法

返回负数：o1 小于 o2。

返回零：o1 等于 o2。

返回正数：o1 大于 o2。

int compare(T o1, T o2)定义两个对象的比较逻辑。
boolean equals(Object obj)（默认实现）：用于比较当前 Comparator 与另一个对象是否相等。
常见用法

.匿名内部类直接实现接口并定义排序逻辑。

a.Lambda 表达式在 Java 8 之后，更简洁地实现比较逻辑。

b.方法引用使用已有的方法简化代码。

c.Comparator 的引入极大地提高了排序的灵活性，适用于需要多条件或动态排序的场景。

项目配置

pom.xml 配置

<dependencies>
    <!-- Spring Boot Starter -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>

    <!-- Spring Boot Thymeleaf -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-thymeleaf</artifactId>
    </dependency>

    <!-- Lombok -->
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>

    <!-- Spring Boot DevTools -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
        <scope>runtime</scope>
    </dependency>

    <!-- Spring Boot Configuration Processor -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-configuration-processor</artifactId>
        <optional>true</optional>
    </dependency>
</dependencies>

application.yaml 配置

custom:
  sorting:
    criteria:
      - name
      - age
      - city

读取配置类

package com.icoderoad.config;


import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;


import java.util.List;


@Data
@Configuration
@ConfigurationProperties(prefix = "custom.sorting")
public class SortingConfig {
    private List<String> criteria;
}

核心代码

实体类

package com.icoderoad.entity;


import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;


@Data
@NoArgsConstructor
@AllArgsConstructor
public class Person {
    private String name;
    private int age;
    private String city;
}

Comparator 实现

package com.icoderoad.util;


import com.icoderoad.entity.Person;


import java.util.Comparator;


public class PersonComparator {
    public static Comparator<Person> byName() {
        return Comparator.comparing(Person::getName);
    }


    public static Comparator<Person> byAge() {
        return Comparator.comparingInt(Person::getAge);
    }


    public static Comparator<Person> byCity() {
        return Comparator.comparing(Person::getCity);
    }
}

服务层

package com.icoderoad.service;


import com.icoderoad.config.SortingConfig;
import com.icoderoad.entity.Person;
import com.icoderoad.util.PersonComparator;
import org.springframework.stereotype.Service;


import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;


@Service
public class PersonService {


    private final SortingConfig sortingConfig;


    public PersonService(SortingConfig sortingConfig) {
        this.sortingConfig = sortingConfig;
    }


    public List<Person> sortPersons(List<Person> persons, String criteria) {
        Comparator<Person> comparator;
        switch (criteria) {
            case "age":
                comparator = PersonComparator.byAge();
                break;
            case "city":
                comparator = PersonComparator.byCity();
                break;
            case "name":
            default:
                comparator = PersonComparator.byName();
                break;
        }
        return persons.stream().sorted(comparator).collect(Collectors.toList());
    }
}

控制器层

package com.icoderoad.controller;


import com.icoderoad.entity.Person;
import com.icoderoad.service.PersonService;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;


import java.util.Arrays;
import java.util.List;


@Controller
public class PersonController {


    private final PersonService personService;


    public PersonController(PersonService personService) {
        this.personService = personService;
    }


    @GetMapping("/persons")
    public String getPersons(@RequestParam(defaultValue = "name") String criteria, Model model) {
        List<Person> persons = Arrays.asList(
            new Person("Alice", 30, "New York"),
            new Person("Bob", 25, "San Francisco"),
            new Person("Charlie", 35, "Chicago")
        );
        model.addAttribute("persons", personService.sortPersons(persons, criteria));
        model.addAttribute("criteria", criteria);
        return "persons";
    }
}

前端实现

persons.html 模板

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Person List</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/css/bootstrap.min.css">
</head>
<body>
<div class="container mt-5">
    <h1>人员列表</h1>
    <form method="get" action="/persons">
        <select name="criteria" class="form-select" onchange="this.form.submit()">
            <option value="name" th:selected="${criteria == 'name'}">按姓名排序</option>
            <option value="age" th:selected="${criteria == 'age'}">按年龄排序</option>
            <option value="city" th:selected="${criteria == 'city'}">按城市排序</option>
        </select>
    </form>
    <table class="table table-striped mt-3">
        <thead>
        <tr>
            <th>姓名</th>
            <th>年龄</th>
            <th>城市</th>
        </tr>
        </thead>
        <tbody>
        <tr th:each="person : ${persons}">
            <td th:text="${person.name}"></td>
            <td th:text="${person.age}"></td>
            <td th:text="${person.city}"></td>
        </tr>
        </tbody>
    </table>
</div>
<script src="https://cdn.jsdelivr.net/npm/jquery@3.6.0/dist/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/js/bootstrap.bundle.min.js"></script>
</body>
</html>

通过以上代码，我们展示了如何使用 Java Comparator 实现定制化排序，并在 Spring Boot 项目中将排序功能集成到前后端，最终呈现了一个可交互的人员列表。希望本文能够帮助你深入理解 Comparator 的用法！