背景

在SpringBoot环境中，我们有“使用不完的”注解。这也是SpringBoot替代了传统的Spring项目中的xml配置的原因。在使用这些annotation的时候，我们一定要了解这些注解背后的原理以及约定。

package org.springframework.boot.context.properties;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ConfigurationProperties {
  ......
}

支持的类型

List

custom.config.config1.folders[0]=/root
custom.config.config1.folders[1]=/home/user1
custom.config.config1.folders[2]=/home/user2

对应的Java实现

@ConfigurationProperties(prefix = "custom.config.config1")
public class Config1Properties{
	private List<String> folders;
	...
}

Map

custom.config.config1.map.key1=value1
custom.config.config1.map.key2=value2
custom.config.config1.map.key3=value3
custom.config.config1.map.key4=value4
custom.config.config1.map.key5=value5

对应的Java实现

@ConfigurationProperties(prefix = "custom.config.config1")
public class Config1Properties{
	private Map<String, String> map;
	...
}

Object

custom.config.config1.server.host=host1
custom.config.config1.server.port=22
custom.config.config1.server.username=username1
custom.config.config1.server.password=password1

对应的Java实现

@ConfigurationProperties(prefix = "custom.config.config1")
public class Config1Properties{
	private ServerProperties server;
	...
	public static class ServerProperties {
		private String host;
		private int port;
		private String username;
		private String password;
		...
	}
}

Object List

custom.config.config1.servers[0].host=host1
custom.config.config1.servers[0].port=22
custom.config.config1.servers[0].username=username1
custom.config.config1.servers[0].password=password1
custom.config.config1.servers[1].host=host2
custom.config.config1.servers[1].port=22
custom.config.config1.servers[1].username=username2
custom.config.config1.servers[1].password=password2

对应的Java实现

@ConfigurationProperties(prefix = "custom.config.config1")
public class Config1Properties{
	private List<ServerProperties> servers;
	...
	public static class ServerProperties {
		private String host;
		private int port;
		private String username;
		private String password;
		...
	}
}

Map的使用案例

比如，我们同时需要连接多个OSS（阿里对象存储），那我们就可以利用ConfigurationProperties的方式来配置多个。而且可以通过Spring的加载动态的注入到容器中去。

配置中心的配置：

# OSS1配置
oss.multi.clients.accout.accessKeyId=xxx
oss.multi.clients.accout.accessKeySecret=xxx
oss.multi.clients.accout.privateEndpoint=xxx
oss.multi.clients.accout.bucketName=bucket-b-test

# OSS2配置
oss.multi.enabled=true
oss.multi.clients.xdtrans.accessKeyId=xxx
oss.multi.clients.xdtrans.accessKeySecret=xxx
oss.multi.clients.xdtrans.privateEndpoint=xxx
oss.multi.clients.xdtrans.bucketName=bucket-a-test

对应的Java实现

@Data
@EqualsAndHashCode(callSuper = false)
@ConfigurationProperties(prefix = OssConstants.MULTI_CONFIG_PREFIX)
public class MultiOssProperties {
	private Map<String, OssProperties> clients;

	@Data
	public static class OssProperties {
		private String accessKeyId;
		private String accessKeySecret;
		private String publicEndpoint;
		private String privateEndpoint;
		private String bucketName;
		private String object;
	}

动态的定义我们需要的BeanDefinition。

public class MultiOssScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware {

	private ApplicationContext applicationContext;

	@Setter
	private MultiOssProperties multiOssProperties;

	@Override
	public void setBeanName(String name) {
		log.info("init bean {}", name);
	}

	@Override
	public void afterPropertiesSet() throws Exception {
		Objects.requireNonNull(this.multiOssProperties, "multiOssProperties不能为空");
		Objects.requireNonNull(this.applicationContext, "applicationContext不能为空");
	}

  // 动态的定义Bean
	@Override
	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
		String beanSuffixName = StringUtils.capitalize(OssConstants.BEAN_SUFFIX_NAME);
    // productCodes实际与oss.multi.clients.xdtrans的xdtrans保持一致
		multiOssProperties.getClients().forEach((productCode, ossProperties) -> {
			AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition(OssClient.class,
					() -> OssClientUtils.buildOssClient(ossProperties))
					.getRawBeanDefinition();
			beanDefinition.setInitMethodName("init");
			beanDefinition.setDestroyMethodName("shutDown");
			beanDefinitionRegistry.registerBeanDefinition(productCode + beanSuffixName, beanDefinition);
		});
	}

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
	}

	@Override
	public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
		this.applicationContext = applicationContext;
	}

}

通过binder来让配置与对应的Java代码产生关系：

@Configuration
@EnableConfigurationProperties(MultiOssProperties.class)
@ConditionalOnProperty(prefix = OssConstants.MULTI_CONFIG_PREFIX, value = "enabled")
public class MultiOssAutoConfiguration {

	/**
	 * 初始化多个 ossClient 自动配置
	 *
	 * @param environment 环境变量属性
	 * @return OssClient 自动扫描注册器
	 */
	@Bean
	public MultiOssScannerConfigurer multiOssScannerConfigurer(Environment environment) {
		Binder binder = Binder.get(environment);
		MultiOssProperties properties = binder.bind(OssConstants.MULTI_CONFIG_PREFIX, MultiOssProperties.class).get();
		MultiOssScannerConfigurer multiOssScannerConfigurer = new MultiOssScannerConfigurer();
		multiOssScannerConfigurer.setMultiOssProperties(properties);
		return multiOssScannerConfigurer;
	}
}

如何使用?

@Getter
@AllArgsConstructor
public enum OssTypeEnum {
		// 注意一下这里的beanName,要跟上面的postProcessBeanDefinitionRegistry保持一致
    XDtransOssClient("xdtransOssClient", "oss1"),
    DianDianOssClient("ddacctOssClient", "oss2"),
    ;

    private final String beanName;
    private final String desc;

    // 根据BeanName来Spring容器中获取即可
    public OssClient getBean() {
        return SpringContextHolder.getBean(beanName, OssClient.class);
    }

Binder是如何映射的？

通过上面的代码binder.bind(OssConstants.MULTI_CONFIG_PREFIX, MultiOssProperties.class).get();来进行bind。

protected final <T> T bind(ConfigurationPropertyName name, Bindable<T> target, BindHandler handler, Context context, boolean allowRecursiveBinding) {
		context.clearConfigurationProperty();
		try {
			target = handler.onStart(name, target, context);
			if (target == null) {
				return null;
			}
			Object bound = bindObject(name, target, handler, context,allowRecursiveBinding);
			return handleBindResult(name, target, handler, context, bound);
		} catch (Exception ex) {
			return handleBindError(name, target, handler, context, ex);
		}
}

如果我们的key是：oss.multi.clients.accout.xxx

实际上对应的是Map，那么它的引用名字就是clients。具体的key就是accout，那么对应的value就是OssProperties。

private Object bindBean(ConfigurationPropertyName name, Bindable<?> target,
		BindHandler handler, Context context, boolean allowRecursiveBinding) {
	if (containsNoDescendantOf(context.getSources(), name)
			|| isUnbindableBean(name, target, context)) {
		return null;
	}
	BeanPropertyBinder propertyBinder = (propertyName, propertyTarget) -> bind(
			name.append(propertyName), propertyTarget, handler, context, false);
	Class<?> type = target.getType().resolve(Object.class);
	if (!allowRecursiveBinding && context.hasBoundBean(type)) {
		return null;
	}
	return context.withBean(type, () -> {
		Stream<?> boundBeans = BEAN_BINDERS.stream()
				.map((b) -> b.bind(name, target, context, propertyBinder));
		return boundBeans.filter(Objects::nonNull).findFirst().orElse(null);
	});
}

https://p1-jj.byteimg.com/tos-cn-i-t2oaga2asx/gold-user-assets/2020/5/6/171ea982bbed5909~tplv-t2oaga2asx-image.image

具体的一个bind情况。

private static final List<BeanBinder> BEAN_BINDERS;

static {
	List<BeanBinder> binders = new ArrayList<>();
	binders.add(new JavaBeanBinder());
	BEAN_BINDERS = Collections.unmodifiableList(binders);
}

public <T> T bind(ConfigurationPropertyName name, Bindable<T> target, Context context,
		BeanPropertyBinder propertyBinder) {
	boolean hasKnownBindableProperties = hasKnownBindableProperties(name, context);
	Bean<T> bean = Bean.get(target, hasKnownBindableProperties);
	if (bean == null) {
		return null;
	}
	BeanSupplier<T> beanSupplier = bean.getSupplier(target);
	boolean bound = bind(propertyBinder, bean, beanSupplier);
	return (bound ? beanSupplier.get() : null);
}
// 返回对应的对象
public BeanSupplier<T> getSupplier(Bindable<T> target) {
	return new BeanSupplier<>(() -> {
		T instance = null;
		if (target.getValue() != null) {
			instance = target.getValue().get();
		}
		if (instance == null) {
			instance = (T) BeanUtils.instantiateClass(this.resolvedType);
		}
		return instance;
	});
}

参考地址

https://blog.csdn.net/sayyy/article/details/83657119

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