如何在无HTTP请求下调用Spring Data JPA持久化方法？

我是Spring Data JPA新手，遇到一个入门问题：无法在不带@Controller或HTTP请求相关注解的类中调用持久化方法。我了解CommandLineRunner接口的run方法，但不想把核心代码都写在run方法里，希望像外观模式那样调用其他类及其自有方法。

实体类（Model） #

package com.example.demo;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Expense {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String item;
    private float amount;


    public Expense () {
        
    }
    
    public Expense(String item, float amount) {
        this.item = item;
        this.amount = amount;
    }

    /* Getters and setters */

    @Override
    public String toString() {
        return "Expense{" + "id=" + id + ", item=" + item + ", amount=" + amount + '}';
    }
    
}

Repository接口 #

package com.example.demo;

import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;

@Repository
public interface ExpenseRepository extends JpaRepository<Expense, Long>{
    
    public List<Expense> findByItem (String item);
    
    @Query("SELECT e FROM Expense e WHERE e.amount >= :amount")
    public List<Expense> listItemsWithPriceOver(@Param("amount") float amount);
    
}

持久化操作类 #

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;

public class ExpansePersistence {

    @Autowired
    private ExpenseRepository repository;

    public void expensePersistence() {
        repository.save(new Expense("tomato", 10));
        repository.save(new Expense("banana", 6));
        repository.save(new Expense("apple", 12));
        
        Iterable<Expense> iterator = repository.findAll();

        System.out.println("List all: ");
        iterator.forEach(item -> System.out.println(item.toString()));
    }
    
}

主启动类 #

package com.example.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication implements CommandLineRunner {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        new ExpensePersistence().expensePersistence();
    }

}

报错信息 #

Caused by: java.lang.NullPointerException: Cannot invoke "com.example.demo.ExpenseRepository.findAll()" because "this.repository" is null

解决方案 #

1. 将ExpansePersistence声明为Spring Bean #

Spring的@Autowired仅对Spring容器管理的Bean生效，直接通过new创建的对象不在容器管理范围内，因此repository无法被注入，导致空指针。给ExpansePersistence添加@Component（或语义更贴合业务的@Service）注解：

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service; // 用@Service更贴合业务逻辑类

@Service
public class ExpansePersistence {

    @Autowired
    private ExpenseRepository repository;

    public void expensePersistence() {
        // 原代码保持不变
    }
    
}

2. 在主类中注入ExpansePersistence而非手动实例化 #

修改DemoApplication，通过@Autowired注入Spring管理的ExpansePersistence Bean，再调用其方法：

package com.example.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.beans.factory.annotation.Autowired;

@SpringBootApplication
public class DemoApplication implements CommandLineRunner {

    @Autowired
    private ExpansePersistence expensePersistence;

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        expensePersistence.expensePersistence();
    }

}

额外提示 #

• 注意类名拼写：ExpansePersistence应为ExpensePersistence（拼写错误少了一个s），建议修正避免后续混淆。
• 业务逻辑类优先使用@Service注解，@Component是通用Bean注解，@Service更具语义性，便于代码维护。

内容的提问来源于stack exchange，提问作者Staniack