手撕spring框架(5)

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手撕spring框架（1）
手撕spring框架（2）
手撕spring框架（3）
手撕spring框架（4）
这是本专题最后一节了，主要是讲述自定义一个注解，实现自定义值的引用，继承BeanPostProcessor接口，在对象创建的时候，注入到变量中。

注解DzendValue接口源码

package com.dzend.service;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;@Retention(java.lang.annotation.RetentionPolicy.RUNTIME
)
@Target(ElementType.FIELD)
public @interface DzendValue {String value() default "";
}

核心是定义一个默认值

定义DzendValueBeanPostProcessor类

package com.dzend.service;import com.spring.BeanPostProcessor;
import com.spring.Component;import java.lang.reflect.Field;@Component
public class DzendValueBeanPostProcessor implements BeanPostProcessor {@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) {for (Field field : bean.getClass().getDeclaredFields()) {if (field.isAnnotationPresent(DzendValue.class)) {field.setAccessible(true);try{field.set(bean,field.getAnnotation(DzendValue.class).value());} catch (IllegalAccessException e) {e.printStackTrace();}}}return bean;}
}

继承BeanPostProcessor接口，并实现在初始后给属性赋值。

使用

在上图标出来的代码是用来实现继承了BeanPostProcessor对象，在createBean的时候，创建完对象，来执行aop这块的业务逻辑，在初始化前和初始化后。
源码：

package com.spring;import java.beans.Introspector;
import java.io.File;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;
import java.net.URLDecoder;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;public class DzendApplicationContext {private Class<?> configClass;private Map<String,BeanDefinition> beanDefinitionMap= new HashMap<>();private Map<String, Object> singletonObjects=new HashMap<>();private List<BeanPostProcessor> beanPostProcessorList = new ArrayList<>();public DzendApplicationContext(Class configClass)   {this.configClass=configClass;scan(configClass);}private void scan(Class configClass) {if(configClass.isAnnotationPresent(ComponentScan.class)){ComponentScan componentScan = (ComponentScan) configClass.getAnnotation(ComponentScan.class);String path = componentScan.value();path = path.replace(".","/");ClassLoader classLoader = DzendApplicationContext.class.getClassLoader();URL resource = classLoader.getResource(path);try {path = URLDecoder.decode(path, "UTF-8");} catch (UnsupportedEncodingException e) {throw new RuntimeException(e);}File file = null;try {file = new File(  URLDecoder.decode(resource.getFile(), "UTF-8"));} catch (UnsupportedEncodingException e) {throw new RuntimeException(e);}if(file.isDirectory()){for (File f : file.listFiles()) {String absolutePath = f.getAbsolutePath();absolutePath = absolutePath.substring(absolutePath.indexOf("com"),absolutePath.indexOf(".class"));absolutePath=absolutePath.replace("\\",".");try {Class<?>  clazz = classLoader.loadClass(absolutePath);if (clazz.isAnnotationPresent(Component.class)) {if (BeanPostProcessor.class.isAssignableFrom(clazz)) {BeanPostProcessor instance = (BeanPostProcessor) clazz.getConstructor().newInstance();beanPostProcessorList.add(instance);}Component componentAnnotaion = clazz.getAnnotation(Component.class);String beanName= componentAnnotaion.value();if("".equals(beanName)){beanName = Introspector.decapitalize(clazz.getSimpleName());}BeanDefinition beanDefinition = new BeanDefinition();beanDefinition.setType(clazz);if (clazz.isAnnotationPresent(Scope.class)) {Scope scopeAnnotation = clazz.getAnnotation(Scope.class);String value = scopeAnnotation.value();beanDefinition.setScope(value);}else{beanDefinition.setScope("singleton");}beanDefinitionMap.put(beanName,beanDefinition);}} catch (ClassNotFoundException e) {e.printStackTrace();} catch (InvocationTargetException e) {throw new RuntimeException(e);} catch (InstantiationException e) {throw new RuntimeException(e);} catch (IllegalAccessException e) {throw new RuntimeException(e);} catch (NoSuchMethodException e) {throw new RuntimeException(e);}}}}}public Object getBean(String beanName){if(!beanDefinitionMap.containsKey(beanName)){throw new NullPointerException();}BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);if(beanDefinition.getScope().equals("singleton")){Object singletonObject = singletonObjects.get(beanName);if(singletonObject == null){singletonObject = createBean(beanName,beanDefinition);singletonObjects.put(beanName,singletonObject);}return singletonObject;}else{//原型Object prototypeBean = createBean(beanName, beanDefinition);return prototypeBean;}}private Object createBean(String beanName, BeanDefinition beanDefinition) {Class clazz = beanDefinition.getType();Object instance = null;try {instance = clazz.getConstructor().newInstance();for (Field field : clazz.getDeclaredFields()) {if(field.isAnnotationPresent(Autowired.class)){field.setAccessible(true);field.set(instance,getBean(field.getName()));}}if(instance instanceof BeanNameAware){((BeanNameAware) instance).setBeanName(beanName);}for (BeanPostProcessor beanPostProcessor : beanPostProcessorList) {instance = beanPostProcessor.postProcessBeforeInitialization(instance,beanName);}if(instance instanceof InitializingBean){((InitializingBean) instance).afterPropertiesSet();}for (BeanPostProcessor beanPostProcessor : beanPostProcessorList) {instance = beanPostProcessor.postProcessAfterInitialization(instance,beanName);}} catch (InstantiationException e) {throw new RuntimeException(e);} catch (IllegalAccessException e) {throw new RuntimeException(e);} catch (InvocationTargetException e) {throw new RuntimeException(e);} catch (NoSuchMethodException e) {throw new RuntimeException(e);}return instance;}
}

以上是最终的代码，本专题基本上讲完了一个简单的spirng框架的实现，是从0开始构建的，希望帮帮助大家对spring有一定的认识，当然，这是只是个简化版本。