原文网址：Spring(SpringBoot)--条件注入--方法/示例_IT利刃出鞘的博客-CSDN博客
简介说明
本文介绍Spring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。
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 @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 | |
| @ConditionalOnExpression | spel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 | |
| @ConditionalOnNotWebApplication | web环境不存在时 | |
| @ConditionalOnWebApplication | web环境存在时 | |
| @ConditionalOnResource | 要求制定的资源存在 |
@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
@ConditionalOnProperty("config1.enable", havingValue="true")
多个值
@ConditionalOnProperty(name={"config1.enable","config.all"}, havingValue="true")
@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。
@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}}")
实例@Component、@Configuration+@Bean都可以与条件注入的注解结合。
@Component + 条件注解Bean
package com.example.config;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.stereotype.Component;
@Component
@ConditionalOnProperty(name = "custom.myComponent.enabled", havingValue = "true")
public class MyComponent {
public MyComponent() {
System.out.println("[MyComponent#MyComponent]");
}
}
application.yml
custom:
myComponent:
enabled: true
运行结果：
[MyComponent#MyComponent]
若将application.yml的custom.myComponent.enabled去掉，或者设置为非true值，则不会输出上边的运行结果。
@Configuration + @Bean + 条件注解Bean
package com.example.config;
public class MyComponent {
public MyComponent() {
System.out.println("[MyComponent#MyComponent]");
}
}
配置类
package com.example.config;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class MyConfig {
@Bean
@ConditionalOnProperty(name = "custom.myComponent.enabled", havingValue = "true")
public MyComponent getMyComponent() {
return new MyComponent();
}
}
application.yml
custom:
myComponent:
enabled: true
运行结果：
[MyComponent#MyComponent]
若将application.yml的custom.myComponent.enabled去掉，或者设置为非true值，则不会输出上边的运行结果。
@Configuration + 条件注解 + @BeanBean
package com.example.config;
public class MyComponent {
public MyComponent() {
System.out.println("[MyComponent#MyComponent]");
}
}
配置类
package com.example.config;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
@ConditionalOnProperty(name = "custom.myComponent.enabled", havingValue = "true")
public class MyConfig {
@Bean
public MyComponent getMyComponent() {
return new MyComponent();
}
}
application.yml
custom:
myComponent:
enabled: true
运行结果：
[MyComponent#MyComponent]
若将application.yml的custom.myComponent.enabled去掉，或者设置为非true值，则不会输出上边的运行结果。
自定义Condition自定义的condition的matches方法返回值为true时，才会创建bean。
条件类
//判断当前系统是否是Mac
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class MyCondition implements Condition {
@Override
public boolean matches(ConditionContext conditionContext,
AnnotatedTypeMetadata annotatedTypeMetadata) {
return conditionContext.getEnvironment().getProperty("os.name").contains("Mac");
}
}
@Configuration
public class Config {
@Conditional(MyCondition.class)
@Bean
public String condition() {
System.err.println("This is mac");
return "";
}
}
其他网址
Spring Boot 2 实战：使用 @Condition 注解来根据条件注入 Bean
Spring注解系列之ConditionalOnProperty_瘦子没有夏天-CSDN博客_conditionalonproperty注解
