承接前文springboot情操陶冶-@Configuration注解解析，本文将在前文的基础上阐述@ConfigurationProperties注解的使用
@ConfigurationProperties
此注解多用于对配置文件的加载以及映射对应值至相应的java属性中，样例如下
1.配置属性指定application.properties
# user custom
user.custom.username=demo_jing
user.custom.nickname=nanco
user.custom.email=questionsky1211@gmail.com
user.custom.password=demo1234
user.custom.job=programmer
2.属性映射类(使用@ConfigurationProperties注解)UserProperty.java
package com.example.demo.bootbase;
import org.springframework.boot.context.properties.ConfigurationProperties;
/**
* @author nanco
* @create 2018/8/13
**/
@ConfigurationProperties(prefix = "user.custom")
public class UserProperty {
private String username;
private String nickname;
private String email;
private String password;
private String job;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getNickname() {
return nickname;
}
public void setNickname(String nickname) {
this.nickname = nickname;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
@Override
public String toString() {
return "UserProperty{" +
"username='" + username + '\'' +
", nickname='" + nickname + '\'' +
", email='" + email + '\'' +
", password='" + password + '\'' +
", job='" + job + '\'' +
'}';
}
}
3.属性映射开启(使用@EnableConfigurationProperties注解)UserPropertiesAutoConfiguration.java
package com.example.demo.bootbase;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Configuration;
/**
* @author nanco
* @create 2018/8/13
**/
@Configuration
@EnableConfigurationProperties(value = UserProperty.class)
public class UserPropertiesAutoConfiguration {
}
4.上述注解生效入口META-INF\spring.fatories
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.example.demo.bootbase.UserPropertiesAutoConfiguration
5.结果检验
package com.example.demo;
import com.example.demo.bootbase.UserProperty;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
@SpringBootApplication
public class DemoSpringbootApplication {
public static void main(String[] args) {
ApplicationContext demoApplicationContext = SpringApplication.run(DemoSpringbootApplication.class, args);
UserProperty userProperty = demoApplicationContext.getBean(UserProperty.class) ;
System.out.println(userProperty);
}
}
输出结果如下
...
...
2018-08-13 14:37:05.537 INFO 17384 --- [ main] o.s.c.support.DefaultLifecycleProcessor : Starting beans in phase 2147483647
2018-08-13 14:37:05.546 INFO 17384 --- [ main] c.e.demo.DemoSpringbootApplication : Started DemoSpringbootApplication in 2.611 seconds (JVM running for 3.756)
UserProperty{username='demo_jing', nickname='nanco', email='questionsky1211@gmail.com', password='demo1234', job='programmer'}
出现的结果与我们预知的一样，属性都进行了相应的赋予。下面笔者开展下源码层的解析以解开其中的绑定小谜团
@EnableConfigurationProperties
要想上述的结果运行成功，必须在相应的启动类使用@EnableConfigurationProperties注解，我们先看下其源码
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EnableConfigurationPropertiesImportSelector.class)
public @interface EnableConfigurationProperties {
/**
* Convenient way to quickly register {@link ConfigurationProperties} annotated beans
* with Spring. Standard Spring Beans will also be scanned regardless of this value.
* @return {@link ConfigurationProperties} annotated beans to register
*/
Class<?>[] value() default {};
}
其中的value属性便是扫描的属性class，并且会将指定的class属性注册至bean工厂。通过前文分析可得，最终的解析是通过@Import引入的EnableConfigurationPropertiesImportSelector.class来实现的
EnableConfigurationPropertiesImportSelector
直接查看其复写的selectImports()方法
private static final String[] IMPORTS = {
// 属性类注册
ConfigurationPropertiesBeanRegistrar.class.getName(),
// 属性类绑定处理
ConfigurationPropertiesBindingPostProcessorRegistrar.class.getName() };
@Override
public String[] selectImports(AnnotationMetadata metadata) {
return IMPORTS;
}
将导入两个类去处理属性的关系，我们按照顺序来分析
ConfigurationPropertiesBeanRegistrar
直接去看其复写的方法
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
// 读取被注解类上的EnableConfigurationProperties上的value属性并进行注入至bean工厂
getTypes(metadata).forEach((type) -> register(registry,
(ConfigurableListableBeanFactory) registry, type));
}
具体的代码就不贴出来了，笔者此处作下小的总结
优先读取被注解类上
@EnableConfigurationProperties的value属性在将上述的value属性指定的class集合注入至bean工厂前，优先判断是否被
@ConfigurationProperties注解修饰过，没有则会报错将指定的class集合注册至bean工厂
ConfigurationPropertiesBindingPostProcessorRegistrar
直接查看复写的方法
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
if (!registry.containsBeanDefinition(
ConfigurationPropertiesBindingPostProcessor.BEAN_NAME)) {
// ConfigurationPropertiesBindingPostProcessor注册
registerConfigurationPropertiesBindingPostProcessor(registry);
// ConfigurationBeanFactoryMetadata注册
registerConfigurationBeanFactoryMetadata(registry);
}
}
主要注册了两个beanDefinition，分别是ConfigurationPropertiesBindingPostProcessor类和ConfigurationBeanFactoryMetadata类。
看来具体的属性绑定就是这两个类来处理了，笔者继续往下分析
ConfigurationBeanFactoryMetadata
根据spring的bean的生命周期，实现BeanFactoryPostProcessor接口类中的postProcessBeanFactory()方法优先执行
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
throws BeansException {
this.beanFactory = beanFactory;
for (String name : beanFactory.getBeanDefinitionNames()) {
BeanDefinition definition = beanFactory.getBeanDefinition(name);
String method = definition.getFactoryMethodName();
String bean = definition.getFactoryBeanName();
if (method != null && bean != null) {
this.beansFactoryMetadata.put(name, new FactoryMetadata(bean, method));
}
}
}
其主要用于获取bean工厂上实现被@Bean注解修饰的方法的bean对象，表明@ConfigurationProperties也可以用于修饰method方法上用于动态注入
ConfigurationPropertiesBindingPostProcessor
根据spring的bean的生命周期，首先我们看下其afterPropertiesSet()实现方法
@Override
public void afterPropertiesSet() throws Exception {
// 获取ConfigurationBeanFactoryMetadata实体类
this.beanFactoryMetadata = this.applicationContext.getBean(
ConfigurationBeanFactoryMetadata.BEAN_NAME,
ConfigurationBeanFactoryMetadata.class);
// 创建属性绑定类
this.configurationPropertiesBinder = new ConfigurationPropertiesBinder(
this.applicationContext, VALIDATOR_BEAN_NAME);
}
再而我们看下其postProcessBeforeInitialization()方法
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
throws BeansException {
// 查找是否bean上对应的class上含有ConfigurationProperties注解
ConfigurationProperties annotation = getAnnotation(bean, beanName,
ConfigurationProperties.class);
if (annotation != null) {
// 开始绑定操作
bind(bean, beanName, annotation);
}
return bean;
}
Ok，我们继续往下追踪bind()方法
private void bind(Object bean, String beanName, ConfigurationProperties annotation) {
ResolvableType type = getBeanType(bean, beanName);
// 查看类上是否含有@Validated注解
Validated validated = getAnnotation(bean, beanName, Validated.class);
Annotation[] annotations = (validated != null
? new Annotation[] { annotation, validated }
: new Annotation[] { annotation });
// class/实例/注解 三个绑定在一起供下述调用
Bindable<?> target = Bindable.of(type).withExistingValue(bean)
.withAnnotations(annotations);
try {
this.configurationPropertiesBinder.bind(target);
}
catch (Exception ex) {
throw new ConfigurationPropertiesBindException(beanName, bean, annotation,
ex);
}
}
最终的如何绑定本文就不讲解了，主要会读取Environment的属性然后进行对比绑定。
涉及的代码很多，有兴趣的读者可自行分析。
所以基于上述的此加工类的作用，用户也可以直接通过@Bean注解创建Bean
// 直接返回实例，具体的内部属性的绑定则会由ConfigurationPropertiesBindingPostProcessor加工类完成
@Bean
public UserProperty userProperty(){
return new UserProperty();
}
小结
如果想在springboot中使用外部源的属性值有两个方法
@PropertySource注解加载外部源，然后通过@Value注解来进行注入即可
@ConfigurationProperties注解修饰javabean，其prefix属性是必须配置的，javabean的内部属性与配置文件指定的属性须一致，并且setter方法必须配置，这样可确保属性设置能成功