FactoryBean

FactoryBean以工厂方式创建Bean，提供更灵活的实例化逻辑。

接口定义

public interface FactoryBean<T> {
    // 返回创建的对象
    T getObject() throws Exception;

    // 返回对象类型
    Class<?> getObjectType();

    // 是否单例
    default boolean isSingleton() {
        return true;
    }
}

基本实现

@Component
public class UserFactoryBean implements FactoryBean<User> {

    private String username;
    private String email;

    @Override
    public User getObject() throws Exception {
        // 自定义创建逻辑
        User user = new User();
        user.setUsername(username);
        user.setEmail(email);
        user.setCreateTime(LocalDateTime.now());
        user.setStatus("active");
        return user;
    }

    @Override
    public Class<?> getObjectType() {
        return User.class;
    }

    @Override
    public boolean isSingleton() {
        return true;  // 单例
    }
}

XML配置

<bean id="user" class="com.example.UserFactoryBean">
    <property name="username" value="admin"/>
    <property name="email" value="admin@example.com"/>
</bean>

<!-- 获取FactoryBean本身，添加&前缀 -->
<bean id="userFactory" class="com.example.UserFactoryBean"/>

创建复杂对象

@Component
public class HttpClientFactoryBean implements FactoryBean<HttpClient> {

    private String baseUrl;
    private int timeout = 5000;
    private int maxConnections = 100;

    @Override
    public HttpClient getObject() throws Exception {
        HttpClientBuilder builder = HttpClientBuilder.create();
        builder.setConnectTimeout(timeout);
        builder.setMaxConnTotal(maxConnections);

        HttpClient client = builder.build();
        client.setBaseUrl(baseUrl);
        return client;
    }

    @Override
    public Class<?> getObjectType() {
        return HttpClient.class;
    }
}

创建代理对象

@Component
public class ServiceProxyFactoryBean implements FactoryBean<Object> {

    private Class<?> serviceInterface;
    private String serviceUrl;

    @Override
    public Object getObject() throws Exception {
        // 创建RPC代理对象
        return Proxy.newProxyInstance(
            serviceInterface.getClassLoader(),
            new Class[]{serviceInterface},
            (proxy, method, args) -> {
                // 远程调用逻辑
                return rpcClient.invoke(serviceUrl, method.getName(), args);
            }
        );
    }

    @Override
    public Class<?> getObjectType() {
        return serviceInterface;
    }
}

原型模式

@Component
public class PrototypeFactoryBean implements FactoryBean<Report> {

    @Override
    public Report getObject() throws Exception {
        // 每次调用创建新实例
        return new Report(UUID.randomUUID().toString());
    }

    @Override
    public Class<?> getObjectType() {
        return Report.class;
    }

    @Override
    public boolean isSingleton() {
        return false;  // 原型模式
    }
}

获取FactoryBean本身

@Autowired
@Qualifier("user")  // 获取User对象
private User user;

@Autowired
@Qualifier("&user")  // 获取FactoryBean本身
private UserFactoryBean userFactory;

// 或通过ApplicationContext
Object bean = context.getBean("user");      // User对象
FactoryBean factory = (FactoryBean) context.getBean("&user");  // FactoryBean

实际应用场景

MyBatis SqlSessionFactory

// Spring集成MyBatis的FactoryBean
public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>,
        InitializingBean, ApplicationListener<ApplicationEvent> {

    private DataSource dataSource;
    private Resource[] mapperLocations;

    @Override
    public SqlSessionFactory getObject() throws Exception {
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        Configuration configuration = buildConfiguration();
        return builder.build(configuration);
    }

    @Override
    public Class<?> getObjectType() {
        return SqlSessionFactory.class;
    }
}

动态数据源

@Component
public class DynamicDataSourceFactoryBean implements FactoryBean<DataSource> {

    private Map<String, DataSourceConfig> configs;

    @Override
    public DataSource getObject() throws Exception {
        Map<Object, Object> targetDataSources = new HashMap<>();
        for (Map.Entry<String, DataSourceConfig> entry : configs.entrySet()) {
            targetDataSources.put(entry.getKey(), createDataSource(entry.getValue()));
        }

        DynamicRoutingDataSource routingDataSource = new DynamicRoutingDataSource();
        routingDataSource.setTargetDataSources(targetDataSources);
        routingDataSource.setDefaultTargetDataSource(
            targetDataSources.get("default"));
        return routingDataSource;
    }

    @Override
    public Class<?> getObjectType() {
        return DataSource.class;
    }
}

与普通Bean对比

要点总结

• FactoryBean通过getObject()方法创建Bean实例
• getObjectType()定义返回类型
• isSingleton()控制单例/原型模式
• "&beanName"获取FactoryBean本身
• 适合创建复杂对象、代理对象、整合第三方框架