Java 注解@PostConstruct的原理及使用场景

import javax.annotation.PostConstruct;
public class MyBean {
    @PostConstruct
    public void init() {
        // 执行一些初始化操作
        System.out.println("Bean 已初始化！");
    }
}

import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;
@Component
public class MyService {
    @PostConstruct
    public void setup() {
        // 进行初始化操作
        System.out.println("MyService 已初始化！");
    }
}

@Component
public class ConfigService {
    private Map<String, String> configMap;
    @PostConstruct
    public void init() {
        // 从配置文件或数据库加载配置
        this.configMap = loadConfigurations();
        System.out.println("配置加载完毕！");
    }
    private Map<String, String> loadConfigurations() {
        // 模拟加载配置
        return Map.of("config1", "value1", "config2", "value2");
    }
}

@Component
public class DatabaseService {
    private Connection connection;
    @PostConstruct
    public void init() {
        try {
            this.connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "user", "password");
            System.out.println("数据库连接成功！");
        } catch (SQLException e) {
            System.out.println("数据库连接失败！");
        }
    }
}

@Component
public class EmailService {
    private String smtpServer;
    public EmailService(String smtpServer) {
        this.smtpServer = smtpServer;
    }
    @PostConstruct
    public void validate() {
        if (smtpServer == null || smtpServer.isEmpty()) {
            throw new IllegalArgumentException("SMTP 服务器配置无效！");
        }
        System.out.println("EmailService 验证通过！");
    }
}

@Component
public class TaskSchedulerService {
    @PostConstruct
    public void startTasks() {
        // 启动定时任务
        System.out.println("启动后台任务！");
        // scheduleTask();
    }
}

@Component
public class CacheService {
    private Map<String, String> cache = new HashMap<>();
    @PostConstruct
    public void preloadCache() {
        // 加载缓存数据
        cache.put("user1", "data1");
        cache.put("user2", "data2");
        System.out.println("缓存已加载！");
    }
}