Spring Architecture Series-9.Understanding Design Patterns Through Spring Framework Implementation
Table of Contents
Understanding Design Patterns Through Spring Framework Implementation
Introduction
Design pattern are reusable solutions to common soft ware design problems.The Spring Framework is a perfect example of how design patterns can be effectively applied to create a robust and flexible application framework. In this article,I’ll explore the key design patterns used in my miniSpring implementation.
Core Design Patterns
1. Factory Pattern
The Factory Pattern is central to Spring’s IoC container:
public interface BeanFactory {
Object getBean(String beanName) throws BeansException;
boolean containsBean(String name);
boolean isSingleton(String name);
boolean isPrototype(String name);
Class<?> getType(String name);
}
Implementation example
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
implements ConfigurableListableBeanFactory {
protected Map<String, BeanDefinition> beanDefinitionMap =
new ConcurrentHashMap<>(256);
@Override
public Object getBean(String beanName) throws BeansException {
Object singleton = getSingleton(beanName);
if (singleton == null) {
singleton = createBean(beanName);
}
return singleton;
}
}
Kay aspects:
- Object creation abstraction
- Dependency management
- Lifecycle control
2. Proxy Pattern
The Proxy Pattern is used extensively in Spring’s AOP implementation:
public class JdkDynamicAopProxy implements AopProxy, InvocationHandler {
private Object target;
private PointcutAdvisor advisor;
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
if (this.advisor.getPointcut().getMethodMatcher()
.matches(method, target.getClass())) {
MethodInterceptor interceptor = advisor.getMethodInterceptor();
MethodInvocation invocation = new ReflectiveMethodInvocation(
proxy, target, method, args, target.getClass());
return interceptor.invoke(invocation);
}
return method.invoke(target, args);
}
}
Features:
- Dynamic proxy creation
- Method interception
- Advice application
3. Observer Pattern
The Observer Pattern is implemented in Spring’s event mechanism:
public interface ApplicationListener<E extends ApplicationEvent>
extends EventListener {
void onApplicationEvent(E event);
}
public class SimpleApplicationEventPublisher
implements ApplicationEventPublisher {
private List<ApplicationListener> listeners = new ArrayList<>();
@Override
public void publishEvent(ApplicationEvent event) {
for (ApplicationListener listener : listeners) {
listener.onApplicationEvent(event);
}
}
}
Key aspects:
- Event publishing
- Listener registration
- Event handling
4. Template Method Pattern
The Template Method Pattern is used in JDBC operation:
public class JdbcTemplate {
public Object query(String sql, Object[] args,
PreparedStatementCallBack pstmtCallBack) {
Connection con = null;
PreparedStatement pstmt = null;
try {
con = dataSource.getConnection();
pstmt = con.prepareStatement(sql);
ArgumentPreparedStatementSetter setter =
new ArgumentPreparedStatementSetter(args);
setter.setValues(pstmt);
return pstmtCallBack.doInPreparedStatement(pstmt);
} finally {
// Resource cleanup
}
}
}
Features:
- Algorithm skeleton
- Customizable steps
- Resource management
5. Strategy Pattern
The Strategy Pattern is used in various parts of Spring:
public interface Pointcut {
MethodMatcher getMethodMatcher();
}
public class NameMatchMethodPointcut implements Pointcut {
private String mappedName = "";
@Override
public MethodMatcher getMethodMatcher() {
return new MethodMatcher() {
@Override
public boolean matches(Method method, Class<?> targetClass) {
return mappedName.equals(method.getName());
}
};
}
}
Key aspects:
- Algorithm selection
- Runtime configuration
- Extensibility
Pattern Integration
1. Factory and Proxy Integration
public class ProxyFactoryBean implements FactoryBean<Object> {
private Object target;
private PointcutAdvisor advisor;
@Override
public Object getObject() throws Exception {
return createAopProxy().getProxy();
}
protected AopProxy createAopProxy() {
return getAopProxyFactory().createAopProxy(target, this.advisor);
}
}
2. Observer and Template Method Integration
public abstract class AbstractApplicationContext
implements ApplicationContext {
private ApplicationEventPublisher applicationEventPublisher;
public void refresh() throws BeansException {
// Template method steps
initApplicationEventPublisher();
registerListeners();
finishRefresh();
}
protected void finishRefresh() {
// Observer pattern usage
publishEvent(new ContextRefreshedEvent(this));
}
}
Design Pattern Benefits
1. Flexibility
- Easy to extend
- Loose coupling
- Runtime configuration
2. Maintainability
- Clear structure
- Separation of concerns
- Reusable components
3. Scalability
- Modular design
- Efficient resource management
- Performance optimization
Best Practices
1. Pattern Selection
- Match pattern to problem
- Consider trade-offs
- Avoid over-engineering
2. Implementation
- Clean interfaces
- Proper abstraction
- Error handling
3. Integration
- Pattern combination
- Resource management
- Performance consideration
Common Challenges and Solutions
- Complexity Management
- Clear hierarchy
- Interface segregation
- Documentation
- Performance
- Caching strategies
- Resource pooling
- Lazy initialization
- Extensibility
- Extension points
- Plugin architecture
- Custom implementations
Conclusion
Understanding design patterns through Spring implementation provides:
- Deep insight into pattern usage
- Practical application examples
- Best practice guidelines
- Problem-solving strategies Key takeaways:
- Pattern selection criteria
- Implementation techniques
- Integration approaches
- Performance considerations
This implementation demonstrates how design patterns can be effectively combined to create a robust and flexible framework.