💡 一文彻底弄懂 Spring Boot 自动装配的过程！深入探索与案例解析

环境说明：Windows 10 + IntelliJ IDEA 2021.3.2 + Jdk 1.8

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

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
}

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration

@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
    return SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class, classLoader);
}

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.26</version>
</dependency>

spring.datasource.url=jdbc:mysql://localhost:3306/test
spring.datasource.username=root
spring.datasource.password=password

@Autowired
private DataSource dataSource;

public void testConnection() {
    try (Connection conn = dataSource.getConnection()) {
        System.out.println("连接成功：" + conn);
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

@Configuration
@ConditionalOnClass(DataSource.class)
public class DataSourceAutoConfiguration {
    // 自动配置数据源的代码
}

@Bean
@ConditionalOnProperty(name = "custom.feature.enabled", havingValue = "true")
public MyCustomFeature customFeature() {
    return new MyCustomFeature();
}

import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;

public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
            .antMatchers("/admin/**").authenticated()  // 仅允许认证用户访问
            .antMatchers("/public/**").permitAll()     // 允许所有用户访问
            .and()
            .formLogin();
    }
}

spring.rabbitmq.host=localhost
spring.rabbitmq.port=5672
spring.rabbitmq.username=guest
spring.rabbitmq.password=guest

<!-- MySQL 数据库依赖 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

<!-- Redis 缓存依赖 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

<!-- RabbitMQ 消息队列依赖 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-amqp</artifactId>
</dependency>

# 数据库配置
spring.datasource.url=jdbc:mysql://localhost:3306/userdb
spring.datasource.username=root
spring.datasource.password=password

# Redis 缓存配置
spring.redis.host=localhost
spring.redis.port=6379

# RabbitMQ 配置
spring.rabbitmq.host=localhost
spring.rabbitmq.port=5672
spring.rabbitmq.username=guest
spring.rabbitmq.password=guest

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.stereotype.Service;

@Service
public class UserService {

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Autowired
    private RedisTemplate<String, User> redisTemplate;

    @Autowired
    private RabbitTemplate rabbitTemplate;

    public void addUser(User user) {
        // 保存用户到数据库
        jdbcTemplate.update("INSERT INTO users (id, name) VALUES (?, ?)", user.getId(), user.getName());

        // 缓存用户信息
        redisTemplate.opsForValue().set("user:" + user.getId(), user);

        // 发送消息到消息队列
        rabbitTemplate.convertAndSend("userQueue", "User added: " + user.getName());
    }

    public User getUser(int id) {
        // 优先从缓存获取用户信息
        User user = redisTemplate.opsForValue().get("user:" + id);
        if (user == null) {
            // 缓存未命中，从数据库获取并更新缓存
            user = jdbcTemplate.queryForObject("SELECT * FROM users WHERE id = ?", new Object[]{id}, new UserRowMapper());
            redisTemplate.opsForValue().set("user:" + id, user);
        }
        return user;
    }
}

public static void main(String[] args) {
    ApplicationContext context = SpringApplication.run(MyApp.class, args);
    UserService userService = context.getBean(UserService.class);

    User user = new User(1, "Alice");
    userService.addUser(user);

    User retrievedUser = userService.getUser(1);
    System.out.println("Retrieved user: " + retrievedUser.getName());
}