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概述
BeanPostProcessor ConfigurationPropertiesBindingPostProcessor的作用是绑定PropertySources到@ConfigurationProperties注解的bean实例。这是一个框架内部工具，在实例化每一个bean时，框架会使用它将@ConfigurationProperties注解中指定前缀的外部配置属性项加载进来设置到bean相应的属性上。这里的PropertySources能够从上下文中的Environment对象获取外部配置属性项。
ConfigurationPropertiesBindingPostProcessor所处理的配置属性对象bean和注解@ConfigurationProperties的使用举例:
@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
// ServerProperties 是一个配置属性对象，会以一个bean的形式注册到容器
public class ServerProperties {
/**
* Server HTTP port.
*/
private Integer port;
/**
* Network address to which the server should bind.
*/
private InetAddress address;
// ...
}
源代码解析
package org.springframework.boot.context.properties;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.boot.context.properties.bind.Bindable;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.core.Ordered;
import org.springframework.core.PriorityOrdered;
import org.springframework.core.ResolvableType;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.core.env.PropertySources;
import org.springframework.validation.annotation.Validated;
/**
*
* @author Dave Syer
* @author Phillip Webb
* @author Christian Dupuis
* @author Stephane Nicoll
* @author Madhura Bhave
*/
public class ConfigurationPropertiesBindingPostProcessor implements BeanPostProcessor,
PriorityOrdered, ApplicationContextAware, InitializingBean {
/**
* The bean name that this post-processor is registered with.
*/
public static final String BEAN_NAME = ConfigurationPropertiesBindingPostProcessor.class
.getName();
/**
* The bean name of the configuration properties validator.
*/
public static final String VALIDATOR_BEAN_NAME = "configurationPropertiesValidator";
private ConfigurationBeanFactoryMetadata beanFactoryMetadata;
private ApplicationContext applicationContext;
private ConfigurationPropertiesBinder configurationPropertiesBinder;
// ApplicationContextAware 接口定义的方法
@Override
public void setApplicationContext(ApplicationContext applicationContext)
throws BeansException {
this.applicationContext = applicationContext;
}
// InitializingBean 定义的 该bean 的初始化方法
// 注意每个 BeanPostProcessor 也是一个 bean, 这里指的是该 BeanPostProcessor bean
// 的初始化方法，而不是该BeanPostProcessor要应用的bean实例的初始化方法
@Override
public void afterPropertiesSet() throws Exception {
// We can't use constructor injection of the application context because
// it causes eager factory bean initialization
this.beanFactoryMetadata = this.applicationContext.getBean(
ConfigurationBeanFactoryMetadata.BEAN_NAME,
ConfigurationBeanFactoryMetadata.class);
this.configurationPropertiesBinder = new ConfigurationPropertiesBinder(
this.applicationContext, VALIDATOR_BEAN_NAME);
}
@Override
public int getOrder() {
return Ordered.HIGHEST_PRECEDENCE + 1;
}
// BeanPostProcessor 接口定义的方法
// 在每个bean实例化后，初始化前执行
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
throws BeansException {
ConfigurationProperties annotation = getAnnotation(bean, beanName,
ConfigurationProperties.class);
if (annotation != null) {
// 如果正在创建的bean上带有注解 @ConfigurationProperties ,
// 获取该注解信息，基于此信息进行外部配置属性到正在创建的bean的绑定
bind(bean, beanName, annotation);
}
return bean;
}
// 将注解 @ConfigurationProperties 指定的外部配置属性项设置到目标对象 bean
private void bind(Object bean, String beanName, ConfigurationProperties annotation) {
ResolvableType type = getBeanType(bean, beanName);
Validated validated = getAnnotation(bean, beanName, Validated.class);
Annotation[] annotations = (validated != null)
? new Annotation[] { annotation, validated }
: new Annotation[] { annotation };
Bindable<?> target = Bindable.of(type).withExistingValue(bean)
.withAnnotations(annotations);
try {
this.configurationPropertiesBinder.bind(target);
}
catch (Exception ex) {
throw new ConfigurationPropertiesBindException(beanName, bean, annotation,
ex);
}
}
private ResolvableType getBeanType(Object bean, String beanName) {
Method factoryMethod = this.beanFactoryMetadata.findFactoryMethod(beanName);
if (factoryMethod != null) {
return ResolvableType.forMethodReturnType(factoryMethod);
}
return ResolvableType.forClass(bean.getClass());
}
private <A extends Annotation> A getAnnotation(Object bean, String beanName,
Class<A> type) {
A annotation = this.beanFactoryMetadata.findFactoryAnnotation(beanName, type);
if (annotation == null) {
annotation = AnnotationUtils.findAnnotation(bean.getClass(), type);
}
return annotation;
}
}