实现BeanPostProcessor

本文主要是介绍实现BeanPostProcessor，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1.实现初始化方法

1.目录

2.InitializingBean.java

package com.sunxiansheng.sunspring.processor;/*** Description: Bean的初始化接口* @Author sun* @Create 2024/8/5 16:35* @Version 1.0*/
public interface InitializingBean {/*** 在Bean的所有属性设置完成之后调用*/void afterPropertiesSet();}

3.MonsterService.java 实现初始化接口

package com.sunxiansheng.sunspring.compent;import com.sunxiansheng.sunspring.annotation.Component;
import com.sunxiansheng.sunspring.annotation.Resource;
import com.sunxiansheng.sunspring.annotation.Scope;
import com.sunxiansheng.sunspring.annotation.myenum.MyScope;
import com.sunxiansheng.sunspring.processor.InitializingBean;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;/*** Description: 怪物服务* @Author sun* @Create 2024/8/4 16:31* @Version 1.0*/
// 自定义注解：将MonsterService类交给自定义Spring容器管理
// 如果指定value属性，则使用value属性值作为bean的id，否则使用类名首字母小写作为bean的id
@Component
@Scope(value = MyScope.PROTOTYPE) // 指定bean的作用域为多例
public class MonsterService implements InitializingBean {private static final Logger log = LoggerFactory.getLogger(MonsterService.class);/*** 自定义的Resource注解，用于自动注入MonsterDao对象*/@Resourceprivate MonsterDao monsterDao;public void query() {log.info("MonsterService调用MonsterDao");monsterDao.query();}/*** 初始化方法*/@Overridepublic void afterPropertiesSet() {log.info("MonsterService初始化完成...");}}

4.SunSpringApplicationContext.java 调用初始化方法

5.测试

2.实现后置处理器

1.目录

2.BeanPostProcessor.java 后置处理器接口

package com.sunxiansheng.sunspring.processor;/*** Description: 自定义BeanPostProcessor接口* @Author sun* @Create 2024/8/6 12:36* @Version 1.0*/
public interface BeanPostProcessor {/*** 该方法在bean的初始化方法之前执行* @param bean* @param beanName* @return*/default Object postProcessBeforeInitialization(Object bean, String beanName) {return bean;}/*** 该方法在bean的初始化方法之后执行* @param bean* @param beanName* @return*/default Object postProcessAfterInitialization(Object bean, String beanName) {return bean;}}

3.SunBeanProcessor.java 自定义后置处理器

package com.sunxiansheng.sunspring.compent;import com.sunxiansheng.sunspring.annotation.Component;
import com.sunxiansheng.sunspring.processor.BeanPostProcessor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;/*** Description:* @Author sun* @Create 2024/8/6 12:39* @Version 1.0*/
@Component
public class SunBeanProcessor implements BeanPostProcessor {private static final Logger log = LoggerFactory.getLogger(SunBeanProcessor.class);@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) {log.info("SunBeanProcessor postProcessBeforeInitialization..." + beanName + "=>" + bean.getClass());// 返回空，不对bean进行处理return null;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) {log.info("SunBeanProcessor postProcessAfterInitialization..." + beanName + "=>" + bean.getClass());// 返回空，不对bean进行处理return null;}}

4.SunSpringApplicationContext.java 具体实现

1.定义一个存储后置处理器的List

2.在扫描bean的时候将后置处理器放到List中

3.初始化bean前后使用调用后置处理器进行处理

4.测试

5.完整代码

package com.sunxiansheng.sunspring.ioc;import com.sunxiansheng.sunspring.annotation.Component;
import com.sunxiansheng.sunspring.annotation.ComponentScan;
import com.sunxiansheng.sunspring.annotation.Resource;
import com.sunxiansheng.sunspring.annotation.Scope;
import com.sunxiansheng.sunspring.annotation.myenum.MyScope;
import com.sunxiansheng.sunspring.processor.BeanPostProcessor;
import com.sunxiansheng.sunspring.processor.InitializingBean;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.io.File;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;/*** Description: 自定义Spring容器* @Author sun* @Create 2024/8/4 16:35* @Version 1.0*/
public class SunSpringApplicationContext {private static final Logger log = LoggerFactory.getLogger(SunSpringApplicationContext.class);/*** bean定义的map*/private ConcurrentHashMap<String, BeanDefintion> beanDefintionMap = new ConcurrentHashMap<>();/*** 单例池*/private ConcurrentHashMap<String, Object> singletonObjects = new ConcurrentHashMap<>();/*** bean的后置处理器*/private List<BeanPostProcessor> beanPostProcessorList = new ArrayList<>();// 构造器，接收配置类的class对象public SunSpringApplicationContext(Class<?> configClass) throws ClassNotFoundException, InstantiationException, IllegalAccessException {// 完成bean的扫描，将bean的信息记录到beanDefintionMap中beanDefinitionByScan(configClass);// 初始化单例池initSingletonObjects();}/*** 给某个bean对象完成依赖注入*/private void populateBeans(Object bean) {// 扫描beanDefintionMap中的bean信息，对bean对象中的属性进行依赖注入// 获取Class对象Class<?> clazz = bean.getClass();// 获取所有字段Field[] fields = clazz.getDeclaredFields();// 判断字段上是否有@Resource注解for (Field field : fields) {if (field.isAnnotationPresent(Resource.class)) {// 获取字段名String fieldName = field.getName();// 根据字段名获取bean对象Object beanObject = null;// 从beanDefintionMap中获取bean对象BeanDefintion beanDefintion = beanDefintionMap.get(fieldName);try {// 根据bean的定义信息创建bean对象beanObject = getBean(fieldName);} catch (Exception e) {throw new RuntimeException(e);}// 设置字段可访问field.setAccessible(true);try {// 依赖注入field.set(bean, beanObject);log.info("依赖注入成功：{} => {}.{}", beanObject.getClass(), clazz, fieldName);} catch (IllegalAccessException e) {e.printStackTrace();}}}}/*** 初始化单例池*/private void initSingletonObjects() {// 将beanDefintionMap中的bean信息创建成bean对象放到单例池中beanDefintionMap.forEach((beanName, beanDefintion) -> {try {// 根据bean的定义信息创建bean对象Object bean = createBean(beanDefintion);if (bean != null) {// 将bean对象放到单例池中singletonObjects.put(beanName, bean);}} catch (Exception e) {e.printStackTrace();}});// 打印单例池中的bean对象log.info("根据bean定义信息初始化单例池：{}", singletonObjects);}// 返回容器中的对象public Object getBean(String name) throws Exception {BeanDefintion beanDefintion = beanDefintionMap.get(name);if (beanDefintion == null) {throw new NullPointerException("在bean定义中没有找到bean对象");}// 根据单例和多例来获取bean对象MyScope scope = beanDefintion.getScope();Object bean = null;if (scope == MyScope.SINGLETON) {log.info("getBean单例对象：{}", singletonObjects.get(name));// 单例就直接从单例池中获取对象bean = singletonObjects.get(name);} else {// 多例就创建一个新的对象bean = createProtoTypeBean(beanDefintion);}// 给bean对象完成依赖注入populateBeans(bean);// 记录当前对象，因为后置处理器可能会返回一个新的对象Object current = bean;// 初始化方法之前调用后置处理器 postProcessBeforeInitializationfor (BeanPostProcessor beanPostProcessor : beanPostProcessorList) {Object bean1 = beanPostProcessor.postProcessBeforeInitialization(bean, name);// 如果beanPostProcessor返回的对象为空，则使用原来的对象if (bean1 != null) {current = bean1;}}// 初始化beaninit(current);// 初始化方法之后调用后置处理器 postProcessAfterInitializationfor (BeanPostProcessor beanPostProcessor : beanPostProcessorList) {bean = beanPostProcessor.postProcessAfterInitialization(current, name);// 如果beanPostProcessor返回的对象为空，则使用原来的对象if (bean == null) {bean = current;}}log.info("getBean多例对象：{}", bean);return bean;}/*** 初始化bean* @param bean*/public void init(Object bean) {if (bean instanceof InitializingBean) {((InitializingBean) bean).afterPropertiesSet();}}/*** 根据bean的定义信息创建bean对象（单例bean）* @param beanDefintion* @return* @throws Exception*/private Object createBean(BeanDefintion beanDefintion) throws Exception {// 得到bean的类型Class<?> clazz = beanDefintion.getClazz();// 根据bean的作用域创建bean对象，多例就不创建了，单例就创建if (beanDefintion.getScope() == MyScope.PROTOTYPE) {return null;}Object bean = clazz.getDeclaredConstructor().newInstance();return bean;}/*** 创建多例bean* @param beanDefintion* @return* @throws InstantiationException* @throws IllegalAccessException* @throws InvocationTargetException* @throws NoSuchMethodException*/private static Object createProtoTypeBean(BeanDefintion beanDefintion) throws InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchMethodException {// 多例就创建一个新的对象Class<?> clazz = beanDefintion.getClazz();Object bean = clazz.getDeclaredConstructor().newInstance();return bean;}/*** 完成bean的扫描，将bean的信息记录到beanDefintionMap中* @param configClass* @throws ClassNotFoundException*/private void beanDefinitionByScan(Class<?> configClass) {// 传进来一个配置类的Class对象// 一、获取要扫描的包// 1.首先反射获取类的注解信息ComponentScan componentScan = configClass.getDeclaredAnnotation(ComponentScan.class);// 2.通过注解来获取要扫描的包的路径String path = componentScan.packagePath();log.info("扫描的包路径：{}", path);// 二、得到要扫描包的.class文件对象，从而得到全路径进行反射// 1.获取App类加载器ClassLoader classLoader = SunSpringApplicationContext.class.getClassLoader();// 2.获取要扫描包的真实路径，默认刚开始在根目录下path = path.replace(".", "/");URL resource = classLoader.getResource(path);// 3.由该路径创建一个文件对象，可使用resource.getFile()将URL类型转化为String类型File file = new File(resource.getFile());// 4.遍历该文件夹下的所有.class文件对象if (file.isDirectory()) {File[] files = file.listFiles();for (File f : files) {// 反射注入容器// 1.获取所有文件的绝对路径String absolutePath = f.getAbsolutePath();// 只处理class文件if (absolutePath.endsWith(".class")) {// 2.分割出类名String className = extractClassName(absolutePath);// 3.得到全路径String fullPath = path.replace("/", ".") + "." + className;// 4.判断是否需要注入容器，查看有没有自定义的注解ComponentClass<?> aClass = null;try {aClass = classLoader.loadClass(fullPath);} catch (ClassNotFoundException e) {throw new RuntimeException(e);}// 如果该类使用了注解Component则说明是一个spring beanif (aClass.isAnnotationPresent(Component.class)) {log.info("扫描到Spring Bean：{}", aClass);// 将Bean的后置处理器加入到beanPostProcessorList中// 判断Class对象是否实现了BeanPostProcessor接口if (BeanPostProcessor.class.isAssignableFrom(aClass)) {Object o = null;try {o = aClass.getDeclaredConstructor().newInstance();} catch (Exception e) {log.info("BeanPostProcessor实例化失败：{}", e);}if (o instanceof BeanPostProcessor) {beanPostProcessorList.add((BeanPostProcessor) o);}log.info("BeanPostProcessor实例化成功：{}", o);// 直接跳过，不需要将BeanPostProcessor加入到beanDefintionMap中continue;}// 将bean的信息记录到beanDefintionMap中BeanDefintion beanDefintion = new BeanDefintion();// 1.获取Scope注解的value值if (aClass.isAnnotationPresent(Scope.class)) {Scope scope = aClass.getDeclaredAnnotation(Scope.class);MyScope value = scope.value();// 放到beanDefintion中beanDefintion.setScope(value);} else {// 如果没有指定作用域，则默认为单例beanDefintion.setScope(MyScope.SINGLETON);}beanDefintion.setClazz(aClass);// 2.获取Component注解的value值Component component = aClass.getDeclaredAnnotation(Component.class);String beanName = component.value();if ("".equals(beanName)) {// 如果没有指定value属性，则使用类名首字母小写作为bean的idbeanName = className.substring(0, 1).toLowerCase() + className.substring(1);}// 3.将bean的id和bean的信息放到beanDefintionMap中beanDefintionMap.put(beanName, beanDefintion);} else {log.info("这不是一个Spring Bean={}", aClass);}}}}// 打印beanDefintionMap中的bean信息log.info("将bean定义信息放到beanDefintionMap：{}", beanDefintionMap);}/*** 分割出类名* 类似于 com/sunxiansheng/sunspring/compent/MonsterService.class 的类名* @param filePath* @return*/private String extractClassName(String filePath) {// 获取最后一个 '/' 的位置int lastSlashIndex = filePath.lastIndexOf('/');// 获取最后一个 '.' 的位置int lastDotIndex = filePath.lastIndexOf('.');// 提取两者之间的字符串作为类名return filePath.substring(lastSlashIndex + 1, lastDotIndex);}}

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