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Spring框架基础详解

📂 java ⏱ 2 min 384 words

什么是Spring

Spring是一个轻量级的企业级应用开发框架，核心特性是IoC（控制反转）和AOP（面向切面编程）。

Spring项目结构

src/main/java
  com.example.demo
    controller/
    service/
    repository/
    config/
    model/
src/main/resources
  application.properties
  beans.xml

IoC容器基础

XML配置方式

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="userService" class="com.example.service.UserService">
        <property name="userRepository" ref="userRepository"/>
    </bean>

    <bean id="userRepository" class="com.example.repository.UserRepository"/>
</beans>

Java配置方式

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {
    @Bean
    public UserRepository userRepository() {
        return new UserRepository();
    }

    @Bean
    public UserService userService() {
        return new UserService(userRepository());
    }
}

依赖注入

构造函数注入

import org.springframework.stereotype.Service;

@Service
public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User findById(Long id) {
        return userRepository.findById(id);
    }
}

Setter注入

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

@Service
public class OrderService {
    private UserService userService;

    @Autowired
    public void setUserService(UserService userService) {
        this.userService = userService;
    }
}

字段注入

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

@Service
public class ProductService {
    @Autowired
    private ProductRepository productRepository;

    public Product findByName(String name) {
        return productRepository.findByName(name);
    }
}

Bean作用域

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;

@Configuration
public class BeanScopeConfig {
    @Bean
    @Scope("singleton")
    public SingletonBean singletonBean() {
        return new SingletonBean();
    }

    @Bean
    @Scope("prototype")
    public PrototypeBean prototypeBean() {
        return new PrototypeBean();
    }
}

Bean生命周期

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;

@Component
public class LifecycleBean implements InitializingBean, DisposableBean {
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("Bean初始化完成");
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("Bean销毁");
    }
}

使用ApplicationContext

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class SpringDemo {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context =
            new AnnotationConfigApplicationContext(AppConfig.class);

        UserService userService = context.getBean(UserService.class);
        System.out.println("获取UserService: " + userService);

        String[] beanNames = context.getBeanDefinitionNames();
        System.out.println("所有Bean:");
        for (String name : beanNames) {
            System.out.println("  - " + name);
        }

        context.close();
    }
}

@Component注解

import org.springframework.stereotype.Component;

@Component("myComponent")
public class MyComponent {
    public void doSomething() {
        System.out.println("Component执行操作");
    }
}

import org.springframework.stereotype.Repository;

@Repository
public class UserRepository {
    public User findById(Long id) {
        return new User(id, "张三");
    }
}

import org.springframework.stereotype.Service;

@Service
public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
}

import org.springframework.stereotype.Controller;

@Controller
public class UserController {
    private final UserService userService;

    public UserController(UserService userService) {
        this.userService = userService;
    }
}

配置属性

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;

@Configuration
@PropertySource("classpath:app.properties")
public class PropertyConfig {
    @Value("${app.name}")
    private String appName;

    @Value("${app.version:1.0}")
    private String appVersion;

    public String getAppName() {
        return appName;
    }

    public String getAppVersion() {
        return appVersion;
    }
}

Spring最佳实践

优先使用构造函数注入
使用@Autowired进行自动装配
合理使用Bean作用域
利用@Configuration进行Java配置
使用@Profile区分环境配置

总结

Spring框架通过IoC容器和依赖注入简化了Java企业级应用开发。掌握Spring的核心概念，是学习其他Spring技术的基础。