引言
我们上一篇文章中，已经完成了初始化的过程，十分简单。这次我们将学习BeanPostProcessor，来使我们初始化的过程更加的精细以及灵活。
本文所有的代码都在这个项目工程里，大家需要的时候可以随时取用。传送门
BeanPostProcessor这个接口作用是在初始化前后，对bean进行一些操作，我们首先需要定义接口，代码如下：
package com.zhu.spring;
public interface BeanPostProcessor {
/**
* do something before init
* 初始化之前做一些动作
*/
void postProcessBeforeInitialization(Object bean, String beanName);
/**
* do something after init
* 初始化结束之后做一些动作
*/
void postProcessAfterInitialization(Object bean, String beanName);
}
然后，需要在我们的核心容器类MiniSpringApplicationContext添加一些实现，具体如下：
package com.zhu.spring;
import java.beans.Introspector;
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.Map;
import java.util.concurrent.ConcurrentHashMap;
public class MiniSpringApplicationContext {
private Class configClass;
private Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>();
private Map<String, Object> singletonObjects = new ConcurrentHashMap<>();
private List<BeanPostProcessor> beanPostProcessorList = new ArrayList<>();
public MiniSpringApplicationContext(Class configClass) {
this.configClass = configClass;
//scan the class decorate by @ComponentScan
if(configClass.isAnnotationPresent(ComponentScan.class)){
ComponentScan componentScanAnnotation = (ComponentScan) configClass.getAnnotation(ComponentScan.class);
//scan path, eg: com.zhu.service
String path = componentScanAnnotation.value();
// com.zhu.service ----> com/zhu/service
path = path.replace(".", "/");
//find absolute path from MiniSpringApplicationContext context
ClassLoader classLoader = MiniSpringApplicationContext.class.getClassLoader();
// get url , /Users/knight/IdeaProjects/mini-spring/out/production/mini-spring/com/zhu/service
URL resource = classLoader.getResource(path);
File file = new File(resource.getFile());
if(file.isDirectory()){
File[] files = file.listFiles();
for (File f : files) {
String absolutePath = f.getAbsolutePath();
if(absolutePath.endsWith(".class")){
//real load class
// /Users/knight/IdeaProjects/mini-spring/out/production/mini-spring/com/zhu/service/UserService ---> com.zhu.service.UserService
//com/zhu/service/UserService
String className = absolutePath.substring(absolutePath.indexOf("com"), absolutePath.indexOf(".class"));
//com.zhu.service.UserService
className = className.replace("/", ".");
try {
Class<?> clazz = classLoader.loadClass(className);
if(clazz.isAnnotationPresent(Component.class)){
//新增代码，判断clazz上是否实现或者继承了BeanPostProcessor接口，然后将其加入定义的List中
if(BeanPostProcessor.class.isAssignableFrom(clazz)){
BeanPostProcessor instance = (BeanPostProcessor)clazz.newInstance();
beanPostProcessorList.add(instance);
}
Component componentAnnotation = clazz.getAnnotation(Component.class);
String beanName = componentAnnotation.value();
if("".equals(beanName)){
//transfer name ,eg: Service->service SService->SService, SerR->serR
beanName = Introspector.decapitalize(clazz.getSimpleName());
}
//generate BeanDefinition
BeanDefinition beanDefinition = new BeanDefinition();
beanDefinition.setType(clazz);
if (clazz.isAnnotationPresent(Scope.class)) {
Scope scopeAnnotation = clazz.getAnnotation(Scope.class);
beanDefinition.setScope(scopeAnnotation.value());
}else{
beanDefinition.setScope("singleton");
}
beanDefinitionMap.put(beanName, beanDefinition);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
}
}
//create bean
for (String beanName : beanDefinitionMap.keySet()) {
BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);
if(beanDefinition.getScope().equals("singleton")){
Object bean = createBean(beanName, beanDefinition);
singletonObjects.put(beanName, bean);
}
}
}
private Object createBean(String beanName, BeanDefinition beanDefinition){
Class clazz = beanDefinition.getType();
try {
Object instance = clazz.getConstructor().newInstance();
// simple dependency injection
for (Field field : clazz.getDeclaredFields()) {
if (field.isAnnotationPresent(Autowired.class)) {
//change true ,can assign private
field.setAccessible(true);
String fieldName = field.getName();
Object bean = getBean(fieldName);
field.set(instance, bean);
}
}
//check bean name aware
if (instance instanceof BeanNameAware) {
//force cast to BeanNameAare and call its method
((BeanNameAware)instance).setBeanName(beanName);
}
//新增代码，遍历list，执行before init
//before init
for (BeanPostProcessor beanPostProcessor : beanPostProcessorList) {
beanPostProcessor.postProcessBeforeInitialization(instance, beanName);
}
//check initalizing bean
if (instance instanceof InitializingBean) {
//force cast to BeanNameAare and call its method
((InitializingBean)instance).afterPropertiesSet();
}
//新增代码，遍历list，执行after init
//after init
for (BeanPostProcessor beanPostProcessor : beanPostProcessorList) {
beanPostProcessor.postProcessAfterInitialization(instance, beanName);
}
return instance;
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
public Object getBean(String beanName){
BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);
if(beanDefinition == null){
throw new RuntimeException("class not found with bean name:"+beanName);
}
String scope = beanDefinition.getScope();
if("singleton".equals(scope)){
Object bean = singletonObjects.get(beanName);
if(bean == null){
Object createdBean = createBean(beanName, beanDefinition);
singletonObjects.put(beanName, createdBean);
return createdBean;
}
return bean;
}else{
return createBean(beanName, beanDefinition);
}
}
}
最后，需要在我们的测试类中新增测试代码：
package com.zhu.service;
import com.zhu.spring.BeanPostProcessor;
import com.zhu.spring.Component;
@Component
public class SelfTestBeanPostProcessor implements BeanPostProcessor {
@Override
public void postProcessBeforeInitialization(Object bean, String beanName) {
if(beanName.equals("userService")){
System.out.println("before init bean processor");
}
}
@Override
public void postProcessAfterInitialization(Object bean, String beanName) {
if(beanName.equals("userService")){
System.out.println("after init bean processor");
}
}
}
执行测试类，我们发现一次执行BeanPostProcessor的beforeinit方法，InitializingBean的afterInit方法，BeanPostProcessor的afterinit方法。
结果如下：
before init bean processor
initializing bean —-afterPropertiesSet
after init bean processor
com.zhu.service.OrderService@60e53b93|userService