设计模式实战指南：从源码解析到Java后端架构的艺术

🎯 设计模式实战指南：从源码解析到Java后端架构的艺术

概述

本文档基于设计模式分类，详细介绍Java后端开发中各种设计模式的实际应用场景，结合Spring、MyBatis、Redis等主流框架的源码分析，帮助开发者深入理解设计模式在实践中的价值。

一、创建型模式

1. 单例模式（Singleton Pattern）

应用场景

• 数据库连接池
• 缓存管理器
• 配置管理器
• 日志记录器

Spring框架中的应用

Spring IoC容器本身就是单例模式的典型应用

// Spring ApplicationContext 单例实现
public class AnnotationConfigApplicationContext extends GenericApplicationContext {private final AnnotatedBeanDefinitionReader reader;private final ClassPathBeanDefinitionScanner scanner;public AnnotationConfigApplicationContext() {this.reader = new AnnotatedBeanDefinitionReader(this);this.scanner = new ClassPathBeanDefinitionScanner(this);}
}

Spring Bean的默认作用域就是单例

// Spring BeanFactory 中的单例管理
public class DefaultSingletonBeanRegistry extends FactoryBeanRegistrySupport {// 单例对象缓存private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);protected Object getSingleton(String beanName, boolean allowEarlyReference) {Object singletonObject = this.singletonObjects.get(beanName);if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {// 单例创建逻辑}return singletonObject;}
}

Redis客户端单例应用

// JedisPool 单例模式实现
public class RedisManager {private static volatile JedisPool jedisPool;public static JedisPool getInstance() {if (jedisPool == null) {synchronized (RedisManager.class) {if (jedisPool == null) {JedisPoolConfig config = new JedisPoolConfig();config.setMaxTotal(100);config.setMaxIdle(10);jedisPool = new JedisPool(config, "localhost", 6379);}}}return jedisPool;}
}

2. 工厂方法模式（Factory Method Pattern）

应用场景

• 数据库连接工厂
• 消息队列工厂
• 缓存工厂
• 序列化器工厂

Spring框架中的应用

BeanFactory - Spring的核心工厂

// Spring BeanFactory 接口
public interface BeanFactory {Object getBean(String name) throws BeansException;<T> T getBean(String name, Class<T> requiredType) throws BeansException;<T> T getBean(Class<T> requiredType) throws BeansException;
}// 具体实现类
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactoryimplements ConfigurableListableBeanFactory, BeanDefinitionRegistry {@Overridepublic <T> T getBean(Class<T> requiredType) throws BeansException {return getBean(requiredType, (Object[]) null);}
}

MyBatis中的工厂应用

// MyBatis SqlSessionFactory
public interface SqlSessionFactory {SqlSession openSession();SqlSession openSession(boolean autoCommit);SqlSession openSession(Connection connection);
}// 默认实现
public class DefaultSqlSessionFactory implements SqlSessionFactory {@Overridepublic SqlSession openSession() {return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);}
}

3. 抽象工厂模式（Abstract Factory Pattern）

应用场景

• 数据库访问层抽象
• 消息中间件抽象
• 缓存系统抽象

Spring JDBC中的应用

// 数据源抽象工厂
public interface DataSource extends CommonDataSource, Wrapper {Connection getConnection() throws SQLException;Connection getConnection(String username, String password) throws SQLException;
}// 具体实现
public class HikariDataSource extends HikariConfig implements DataSource {@Overridepublic Connection getConnection() throws SQLException {return getConnection(username, password);}
}

4. 建造者模式（Builder Pattern）

应用场景

• 复杂对象构建
• 配置对象构建
• 查询条件构建

MyBatis中的应用

// MyBatis SqlSessionFactoryBuilder
public class SqlSessionFactoryBuilder {public SqlSessionFactory build(InputStream inputStream) {return build(inputStream, null, null);}public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {try {XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);return build(parser.parse());} catch (Exception e) {throw ExceptionFactory.wrapException("Error building SqlSession.", e);}}
}

Spring Boot配置构建

// Spring Boot ApplicationBuilder
public class SpringApplicationBuilder {private final SpringApplication application;public SpringApplicationBuilder(Class<?>... sources) {this.application = new SpringApplication(sources);}public SpringApplicationBuilder properties(String... defaultProperties) {this.application.setDefaultProperties(StringUtils.toStringArray(defaultProperties));return this;}
}

5. 原型模式（Prototype Pattern）

应用场景

• 对象克隆
• 配置复制
• 模板复制

Spring中的应用

// Spring Bean的prototype作用域
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory