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如何手撸一个java ioc框架

news 来源：原创 2024/7/1 5:33:50

当然可以。下面我会详细解释如何创建一个简单的Java IOC框架。

1. 定义Bean和依赖注入

首先，我们需要定义一个Bean，它是一个Java对象，它的依赖关系可以通过构造函数注入、设值注入或者接口注入来提供。

public class MyService {private AnotherService anotherService;// 构造函数注入public MyService(AnotherService anotherService) {this.anotherService = anotherService;}// ... 方法实现
}
public class AnotherService {// ... 方法实现
}

2. 定义Bean的定义和注册

Bean的定义包含了类的类型、作用域（单例或原型）以及其他元数据。我们需要一个地方来注册这些Bean的定义。

public class BeanDefinition {private Class<?> clazz;private String scope;private List<ConstructorArgument> constructorArguments = new ArrayList<>();private List<Property> properties = new ArrayList<>();// 构造函数、getter和setter
}
public class ConstructorArgument {private int index;private Object value;// 构造函数、getter和setter
}
public class Property {private String name;private Object value;// 构造函数、getter和setter
}

3. 实现BeanFactory

BeanFactory负责创建和管理的Bean实例。它提供了一个getBean方法来获取Bean实例。

public class SimpleBeanFactory implements BeanFactory {private Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>();private Map<String, Object> singletonObjects = new ConcurrentHashMap<>();@Overridepublic Object getBean(String name) throws Exception {BeanDefinition beanDefinition = beanDefinitionMap.get(name);if (beanDefinition == null) {throw new NoSuchBeanDefinitionException(name);}return createBean(beanDefinition);}@Overridepublic void registerBeanDefinition(String name, BeanDefinition beanDefinition) {beanDefinitionMap.put(name, beanDefinition);}private Object createBean(BeanDefinition beanDefinition) throws Exception {if (beanDefinition.getScope().equals("singleton")) {Object singleton = singletonObjects.get(beanDefinition.getClazz());if (singleton == null) {singleton = instantiateBean(beanDefinition);populateBean(singleton, beanDefinition);singletonObjects.put(beanDefinition.getClazz(), singleton);}return singleton;} else {return instantiateBean(beanDefinition);}}private Object instantiateBean(BeanDefinition beanDefinition) throws Exception {Constructor<?> constructor = beanDefinition.getClazz().getDeclaredConstructors()[0];Object[] args = new Object[constructor.getParameterTypes().length];for (int i = 0; i < args.length; i++) {args[i] = getDependency(beanDefinition, constructor.getParameterTypes()[i]);}return constructor.newInstance(args);}private void populateBean(Object bean, BeanDefinition beanDefinition) throws Exception {for (Property property : beanDefinition.getProperties()) {Field field = beanDefinition.getClazz().getDeclaredField(property.getName());field.setAccessible(true);field.set(bean, property.getValue());}}private Object getDependency(BeanDefinition beanDefinition, Class<?> dependencyType) throws Exception {for (ConstructorArgument constructorArgument : beanDefinition.getConstructorArguments()) {if (dependencyType.isAssignableFrom(constructorArgument.getValue().getClass())) {return constructorArgument.getValue();}}return getBean(dependencyType.getName());}
}

4. 使用框架

现在我们可以使用我们的简单IOC框架来创建和配置Bean。

public class Main {public static void main(String[] args) throws Exception {SimpleBeanFactory beanFactory = new SimpleBeanFactory();BeanDefinition myServiceBean = new BeanDefinition();myServiceBean.setClazz(MyService.class);myServiceBean.setScope("singleton");ConstructorArgument arg = new ConstructorArgument();arg.setIndex(0);arg.setValue(new AnotherService());myServiceBean.getConstructorArguments().add(arg);beanFactory.registerBeanDefinition("myService", myServiceBean);MyService myService = (MyService) beanFactory.getBean("myService");myService.someMethod(); // 使用Bean}
}