Spring Architecture Series-4.Building Spring Framework from Scratch: A Learning Path Guide

Introduction Building a Spring-like framework from scratch is an excellent way to deeply understand Spring's core principles and architectural design.In this article,I'll outline a structured learning path based on my experience implementing miniSpring a simplified version of the Spring Framework. Prerequisites Before staring this journey,you should have: Solid understanding of Java Basic knowledge of design patterns Familiarity with dependency injection concepts Understanding of web development basics Knowledge of AOP concepts Phase 1: Core Container (IoC/DI) Step 1: Basic Bean Container Start with the most fundamental part-the 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); } Key learning points: Bean lifecycle management Singleton vs Prototype Basic dependency injection Step 2: Bean Definition Create the blueprint for beans: public class BeanDefinition { private String id; private String className; private String scope = SCOPE_SINGLETON; private PropertyValues propertyValues; private ConstructorArgumentValues constructorArgumentValues; // Getters and setters } Focus area: Bean metadate management Property injection Constructor injection Step 3:Configuration Reading Implement XML configuration support: public class XmlBeanDefinitionReader { public void loadBeanDefinitions(Resource resource) { while (resource.hasNext()) { Element element = (Element) resource.next(); String beanID = element.attributeValue("id"); String beanClassName = element.attributeValue("class"); BeanDefinition beanDefinition = new BeanDefinition(beanID, beanClassName); // Parse properties and register bean definition } } } Learning objectives: XML parsing Resource abstraction Configuration management Phase 2: Advanced Container Features Step 1: Application Context Implement the higher-level container: public class ClassPathXmlApplicationContext extends AbstractApplicationContext { public ClassPathXmlApplicationContext(String fileName) { Resource res = new ClassPathXmlResource(fileName); DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory(); XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory); reader.loadBeanDefinitions(res); } } Focus on: Context initialization Resource loading Bean factory integration Step 2: Bean Post-Processing Add extension points: public interface BeanPostProcessor { Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException; Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException; } Learn about: Bean enhancement Lifecycle hooks Extension mechanisms Phase 3: AOP Implementation Step 1: Basic AOP infrastructure Create the core AOP Interfaces: public interface AopProxy { Object getProxy(); } public class JdkDynamicAopProxy implements AopProxy, InvocationHandler { public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // Implement method interception } } Focus areas: Dynamic proxies Method interception AOP concepts implementation Step 2: Pointcuts And Advisors Implement pointcut matching: public class NameMatchMethodPointcut implements Pointcut { private String mappedName = ""; public MethodMatcher getMethodMatcher() { return new MethodMatcher() { public boolean matches(Method method, Class targetClass) { return mappedName.equals(method.getName()); } }; } } Learn about: Pointcut expressions Method matching Advice types Phase 1: MVC Framework 1: DispatcherServlet Implementation the front controller: public class DispatcherServlet extends HttpServlet { protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HandlerMethod handlerMethod = handlerMapping.getHandler(request); ModelAndView mv = handlerAdapter.handle(request, response, handlerMethod); render(request, response, mv); } } Focus on: Request handling Handler mapping View resolution Step 2:MVC components Create supporting classes: public class ModelAndView { private Object view; private Map model = new HashMap(); // Implementation } @Target(value = {ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) public @interface RequestMapping { String value() default ""; } learn about:

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);
}

public class BeanDefinition {
    private String id;
    private String className;
    private String scope = SCOPE_SINGLETON;
    private PropertyValues propertyValues;
    private ConstructorArgumentValues constructorArgumentValues;

    // Getters and setters
}

public class XmlBeanDefinitionReader {
    public void loadBeanDefinitions(Resource resource) {
        while (resource.hasNext()) {
            Element element = (Element) resource.next();
            String beanID = element.attributeValue("id");
            String beanClassName = element.attributeValue("class");
            BeanDefinition beanDefinition = new BeanDefinition(beanID, beanClassName);
            // Parse properties and register bean definition
        }
    }
}

public class ClassPathXmlApplicationContext extends AbstractApplicationContext {
    public ClassPathXmlApplicationContext(String fileName) {
        Resource res = new ClassPathXmlResource(fileName);
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory);
        reader.loadBeanDefinitions(res);
    }
}

public interface BeanPostProcessor {
    Object postProcessBeforeInitialization(Object bean, String beanName) 
            throws BeansException;
    Object postProcessAfterInitialization(Object bean, String beanName) 
            throws BeansException;
}

public interface AopProxy {
  Object getProxy();
}

public class JdkDynamicAopProxy implements AopProxy, InvocationHandler {
  public Object invoke(Object proxy, Method method, Object[] args)
    throws Throwable {
    // Implement method interception
  }
}

public class NameMatchMethodPointcut implements Pointcut {
    private String mappedName = "";

    public MethodMatcher getMethodMatcher() {
        return new MethodMatcher() {
            public boolean matches(Method method, Class targetClass) {
                return mappedName.equals(method.getName());
            }
        };
    }
}

public class DispatcherServlet extends HttpServlet {
  protected void doDispatch(HttpServletRequest request,
                            HttpServletResponse response) throws Exception {
    HandlerMethod handlerMethod = handlerMapping.getHandler(request);
    ModelAndView mv = handlerAdapter.handle(request, response, handlerMethod);
    render(request, response, mv);
  }
}

public class ModelAndView {
    private Object view;
    private Map<String, Object> model = new HashMap<>();

    // Implementation
}

@Target(value = {ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestMapping {
    String value() default "";
}

public interface PlatformTransactionManager {
    TransactionStatus getTransaction(TransactionDefinition definition);
    void commit(TransactionStatus status);
    void rollback(TransactionStatus status);
}

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