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Spring–条件注入(条件装配)–详解

简介

说明

本文介绍SpringBoot如何将某个类根据条件注入容器。比如:如果某个类不存在,则将类注入;如果某个配置没开启,则不注入。

相关网址

Spring–条件注入(条件装配)–实例 – 自学精灵

源码中的使用

在Spring Boot的源码中,比如涉及到Http编码的自动配置、数据源类型的自动配置等大量的使用到了@ConditionalOnProperty注解。

HttpEncodingAutoConfiguration类中部分源代码:

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(HttpProperties.class)
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
@ConditionalOnClass(CharacterEncodingFilter.class)
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {
    // 省略内部代码
}

DataSourceConfiguration类中部分代码:

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(org.apache.tomcat.jdbc.pool.DataSource.class)
@ConditionalOnMissingBean(DataSource.class)
@ConditionalOnProperty(name = "spring.datasource.type", havingValue = "org.apache.tomcat.jdbc.pool.DataSource",
        matchIfMissing = true)
static class Tomcat {
  // 省略内部代码
}

已有的条件注解

注解大全

注解说明示例
@ConditionalOnProperty要求配置属性匹配条件@ConditionalOnProperty(   prefix = “spring.http.encoding”,   value = “enabled”,   matchIfMissing = true)
@ConditionalOnBean容器中存在对应实例时,返回true。 当给定的类型、类名、注解、昵称在beanFactory中存在时返回true。 若不指定name,则为本bean的名字。@ConditionalOnBean(Abc.class) 或 @ConditionalOnBean(name=”abc”)
@ConditionalOnMissingBean容器中不存在对应实例时,返回true。 当给定的类型、类名、注解、昵称在beanFactory中不存在时返回true。各类型间是or的关系。 若不指定name,则为本bean的名字。
@ConditionalOnClass当给定的类在类路径上存在时返回true,各类型间是and的关系@ConditionalOnClass(Abc.class)
@ConditionalOnMissingClass当给定的类在类路径上不存在时返回true,各类型间是and的关系
@ConditionalOnSingleCandidate当给定类型的bean存在并且指定为Primary的给定类型存在时,返回true
@ConditionalOnCloudPlatform当所配置的CloudPlatform为激活时返回true
@ConditionalOnExpressionspel表达式执行为true详见下方。
@ConditionalOnJava运行时的java版本号是否包含给定的版本号.如果包含,返回匹配,否则,返回不匹配
@ConditionalOnJndi给定的jndi的Location 必须存在一个.否则,返回不匹配
@ConditionalOnNotWebApplicationweb环境不存在时
@ConditionalOnWebApplicationweb环境存在时
@ConditionalOnResource要求制定的资源存在

详解

@ConditionalOnProperty

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
@Documented
@Conditional({OnPropertyCondition.class})
public @interface ConditionalOnProperty {
    String[] value() default {};     //数组,获取对应property名称的值,与name不可同时使用
 
    String prefix() default "";      //property名称的前缀,可有可无
 
    String[] name() default {};      //数组,property完整名称或部分名称(可与prefix组合使用,组成完整的property名称),与value不可同时使用
 
    String havingValue() default "";  //可与name组合使用,比较获取到的属性值与havingValue给定的值是否相同,相同才加载配置
 
    boolean matchIfMissing() default false;  //缺少该property时是否可以加载。如果为true,没有该property也会正常加载;反之报错
}

单个值(key必须存在,且value必须是指定值)

@ConditionalOnProperty(“config1.enable”, havingValue=”true”)

单个值(key必须存在,不关心value)

@ConditionalOnProperty(“config1.enable”)

单个值(key不存在时可以匹配;key存在,value为指定值也匹配)

@ConditionalOnProperty(name = {“config1.enable”}, havingValue=”true”, matchIfMissing=true)

多个值(多个key必须存在,且value必须都是指定值)

@ConditionalOnProperty(name={“config1.enable”,”config.all”}, havingValue=”true”)

多个值(多个key必须存在,不关心value)

@ConditionalOnProperty(name={“config1.enable”,”config.all”})

@ConditionalOnClass

用法1:通过class指定

注意:通过class指定时必须放到有@Configuration的配置类上,不能放到@Bean注解的方法上。

  • 如果放到方法上,启动时会报错:ClassNotFoundException。
  • 如果放到配置类上,不会报错。因为里边捕获了这种异常,不会影响启动。
import a.b.c.Xxx;

@ConditionalOnClass(Xxx.class)

也可以指定多个 

import a.b.c.Xxx;

@ConditionalOnClass({Xxx.class, Yyy.class})

用法2:通过类的全路径名指定 

注意:此方法是在SpringBoot2.2版本开始才有的,要注意兼容性。通过类的全路径名指定时可以放到有@Configuration的配置类上,也可以放到@Bean注解的方法上。

@ConditionalOnClass("a.b.c.Xxx")

也可以指定多个

@ConditionalOnClass({"a.b.c.Xxx", "a.b.c.Yyy"})

源码示例

以openfeign的自动配置类为例:

package org.springframework.cloud.openfeign;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.TimeUnit;

import javax.annotation.PreDestroy;

import com.fasterxml.jackson.databind.Module;
import feign.Client;
import feign.Feign;
import feign.RequestInterceptor;
import feign.httpclient.ApacheHttpClient;
import feign.okhttp.OkHttpClient;
import okhttp3.ConnectionPool;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.HttpClientConnectionManager;
import org.apache.http.impl.client.CloseableHttpClient;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.cloud.client.actuator.HasFeatures;
import org.springframework.cloud.client.circuitbreaker.CircuitBreaker;
import org.springframework.cloud.client.circuitbreaker.CircuitBreakerFactory;
import org.springframework.cloud.commons.httpclient.ApacheHttpClientConnectionManagerFactory;
import org.springframework.cloud.commons.httpclient.ApacheHttpClientFactory;
import org.springframework.cloud.commons.httpclient.OkHttpClientConnectionPoolFactory;
import org.springframework.cloud.commons.httpclient.OkHttpClientFactory;
import org.springframework.cloud.openfeign.security.OAuth2FeignRequestInterceptor;
import org.springframework.cloud.openfeign.support.DefaultGzipDecoderConfiguration;
import org.springframework.cloud.openfeign.support.FeignHttpClientProperties;
import org.springframework.cloud.openfeign.support.PageJacksonModule;
import org.springframework.cloud.openfeign.support.SortJacksonModule;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.security.oauth2.client.OAuth2ClientContext;
import org.springframework.security.oauth2.client.resource.OAuth2ProtectedResourceDetails;

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({ FeignClientProperties.class, FeignHttpClientProperties.class })
@Import(DefaultGzipDecoderConfiguration.class)
public class FeignAutoConfiguration {
    // 省略其他代码

        @Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(OkHttpClient.class)
	@ConditionalOnMissingBean(okhttp3.OkHttpClient.class)
	@ConditionalOnProperty("feign.okhttp.enabled")
	protected static class OkHttpFeignConfiguration {

		private okhttp3.OkHttpClient okHttpClient;

		@Bean
		@ConditionalOnMissingBean(ConnectionPool.class)
		public ConnectionPool httpClientConnectionPool(FeignHttpClientProperties httpClientProperties,
				OkHttpClientConnectionPoolFactory connectionPoolFactory) {
			Integer maxTotalConnections = httpClientProperties.getMaxConnections();
			Long timeToLive = httpClientProperties.getTimeToLive();
			TimeUnit ttlUnit = httpClientProperties.getTimeToLiveUnit();
			return connectionPoolFactory.create(maxTotalConnections, timeToLive, ttlUnit);
		}

		@Bean
		public okhttp3.OkHttpClient client(OkHttpClientFactory httpClientFactory, ConnectionPool connectionPool,
				FeignHttpClientProperties httpClientProperties) {
			Boolean followRedirects = httpClientProperties.isFollowRedirects();
			Integer connectTimeout = httpClientProperties.getConnectionTimeout();
			Boolean disableSslValidation = httpClientProperties.isDisableSslValidation();
			this.okHttpClient = httpClientFactory.createBuilder(disableSslValidation)
					.connectTimeout(connectTimeout, TimeUnit.MILLISECONDS).followRedirects(followRedirects)
					.connectionPool(connectionPool).build();
			return this.okHttpClient;
		}

		@PreDestroy
		public void destroy() {
			if (this.okHttpClient != null) {
				this.okHttpClient.dispatcher().executorService().shutdown();
				this.okHttpClient.connectionPool().evictAll();
			}
		}

		@Bean
		@ConditionalOnMissingBean(Client.class)
		public Client feignClient(okhttp3.OkHttpClient client) {
			return new OkHttpClient(client);
		}

	}
}

注意点:

如果项目中没有引入这个包的话,在Idea中可以看到,它是红色的。但项目在启动时并不会报错,可以正常启动。

原因是:实际我们在引入这个依赖的时候,它的jar包是已经编译好了的。而我们现在这样查看是源码方式查看,不是查看的其jar包的class。

@ConditionalOnExpression

或/与

config1.enabled为true或者config2.enabled 为true

@ConditionalOnExpression(“${config1.enabled:false} || ${config2.enabled:false}”)

与也是类似的:换成&&即可。

计算

@ConditionalOnExpression(“${mq.cumsumer.enabled}==1 && ${rabbitmq.comsumer.enabled:true}”)

取反

config1.enabled为true而且config2.enabled 为false

@ConditionalOnExpression(“${config1.enabled:false} && !${config2.enabled:false}”)

equals

 @ConditionalOnExpression(“‘${mq.comsumer}’.equals(‘rabbitmq’)”)

分级

例2:若局部有配置,按局部配置。否则,按全局配置。若全局、局部都没配置,则不导入。

本处:config2.enabled为局部,config.all.enabled为全局

@ConditionalOnExpression(value = “${config2.enabled:${config.all.enabled:false}}”) ​

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