Spring--条件注入(条件装配)--详解

喜欢ヅ旅行 2023-09-29 12:43 11阅读 0赞

原文网址：[Spring--条件注入(条件装配)--详解\_IT利刃出鞘的博客-CSDN博客][Spring--_--_IT_-CSDN]

## 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\_IT利刃出鞘的博客-CSDN博客][Spring--_--_IT_-CSDN 1]

## **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 ###

<table> 
 <tbody> 
 <tr> 
 <td> 注解 </td> 
 <td> 说明 </td> 
 <td>示例</td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnProperty </td> 
 <td> 要求配置属性匹配条件 </td> 
 <td> @ConditionalOnProperty( &nbsp; prefix = "spring.http.encoding", &nbsp; value = "enabled", &nbsp; matchIfMissing = true) </td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnBean </td> 
 <td> 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。 </td> 
 <td> @ConditionalOnBean(Abc.class) 或 @ConditionalOnBean(name="abc") </td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnMissingBean </td> 
 <td> 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。 </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnClass </td> 
 <td> 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 </td> 
 <td>@ConditionalOnClass(Abc.class)</td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnMissingClass </td> 
 <td> 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 </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnSingleCandidate </td> 
 <td> 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 </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnCloudPlatform </td> 
 <td> 当所配置的CloudPlatform为激活时返回true </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnExpression </td> 
 <td> spel表达式执行为true </td> 
 <td> 详见下方。 </td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnJava </td> 
 <td> 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 </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnJndi </td> 
 <td> 给定的jndi的Location 必须存在一个.否则,返回不匹配 </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnNotWebApplication </td> 
 <td> web环境不存在时 </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnWebApplication </td> 
 <td> web环境存在时 </td> 
 <td></td> 
 </tr> 
 <tr> 
 <td> @ConditionalOnResource </td> 
 <td> 要求制定的资源存在 </td> 
 <td></td> 
 </tr> 
 </tbody> 
</table>

## 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**

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**

@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。

![4a03860f19a8419cad0311a98127350f.png][]

![a3036f630a314fa8a725aacd0ab5f636.png][]

### @ConditionalOnExpression ###

**或/与**

config1.enabled为true或者config2.enabled 为true

@ConditionalOnExpression("$\{config1.enabled:false\} || $\{config2.enabled:false\}")

与时类似。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\}\}")

## **其他网址** ##

[Spring Boot 2 实战：使用 @Condition 注解来根据条件注入 Bean][Spring Boot 2 _ _Condition _ Bean]

[Spring注解系列之ConditionalOnProperty\_瘦子没有夏天-CSDN博客\_conditionalonproperty注解][Spring_ConditionalOnProperty_-CSDN_conditionalonproperty]

[Spring--_--_IT_-CSDN]: https://knife.blog.csdn.net/article/details/124509399
[Spring--_--_IT_-CSDN 1]: https://knife.blog.csdn.net/article/details/125357591
[4a03860f19a8419cad0311a98127350f.png]: https://img-blog.csdnimg.cn/4a03860f19a8419cad0311a98127350f.png
[a3036f630a314fa8a725aacd0ab5f636.png]: https://img-blog.csdnimg.cn/a3036f630a314fa8a725aacd0ab5f636.png
[Spring Boot 2 _ _Condition _ Bean]: https://www.felord.cn/spring-boot-condition.html#1-%E5%89%8D%E8%A8%80
[Spring_ConditionalOnProperty_-CSDN_conditionalonproperty]: https://blog.csdn.net/weixin_39723544/article/details/100652275