重视微信公众号：CodingTechWork，一同学习前进。
需求
在产品对接过程中，一个公共的服务对接多个产品，其间产品A运用RocketMQ进行消费，产品B无需消费。此刻，代码共用了，如何做到产品B能够不消费？
研究了一些方法，首先想到的是如何使RocketMQ的监听消费@RocketMQMessageListener注解失效。研究了一会儿，注解自身没有开关，也没有找到适宜的方法去使指定注解失效。换了另一个方向：条件注解。亲测有用！
@ConditionalOnProperty注解
介绍
- 在
SpringBoot中能够经过该注解来控制@Configuration是否收效。一起，咱们能够经过该注解判别一个property特点，是否契合咱们设定的装备值，契合则使该注解修饰的类或方法收效，否则不收效。 - 该注解是
@Conditional的扩展注解。
源码解析
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//
package org.springframework.boot.autoconfigure.condition;
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.context.annotation.Conditional;
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
@Documented
@Conditional({OnPropertyCondition.class})
public @interface ConditionalOnProperty {
//数组，获取property对应的值，与name特点不能够一起运用
String[] value() default {};
//特点称号值的前缀
String prefix() default "";
//数组，装备特点值的称号，可与prefix组合运用，不可与value特点一起运用
String[] name() default {};
//比较和name特点值获取到的特点值是否相同，与name组合运用，若true，则加载装备
String havingValue() default "";
//缺少装备是否匹配加载，若为true，则表示无该name相关特点值，也加载。反之，不加载。
boolean matchIfMissing() default false;
}
运用示例
新建bean类
@Data
public class PersonBean {
/**
* name
*/
private String name;
/**
* age
*/
private int age;
}
需测验的注解类
/**
* @Description 测验bean装备
* @Author LiaoJy
* @Date 2023/4/17
*/
@Slf4j
@Configuration
@ConditionalOnProperty(prefix = "conditional", name = "configuration.switch", havingValue = "true", matchIfMissing = true)
public class BeanConfigTest {
@Bean
public PersonBean personBean() {
PersonBean personBean = new PersonBean();
personBean.setAge(30);
personBean.setName("andya");
log.info("========person bean init========");
return personBean;
}
}
装备场景一
conditional:
configuration:
switch: false
控制台日志成果
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.6.9)
... ...
2023-04-17 14:14:11.620 INFO 25494 --- [ main] c.test.selfcoding.SelfCodingApplication : No active profile set, falling back to 1 default profile: "default"
2023-04-17 14:14:12.175 INFO 25494 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8001 (http)
2023-04-17 14:14:12.182 INFO 25494 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-04-17 14:14:12.182 INFO 25494 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.64]
2023-04-17 14:14:12.259 INFO 25494 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-04-17 14:14:12.259 INFO 25494 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 609 ms
2023-04-17 14:14:12.445 INFO 25494 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8001 (http) with context path ''
2023-04-17 14:14:12.451 INFO 25494 --- [ main] c.test.selfcoding.SelfCodingApplication : Started SelfCodingApplication in 1.123 seconds (JVM running for 1.387)
成果未打印========person bean init========日志，类未收效。
装备场景二
不装备，或许装备如下
conditional:
configuration:
switch: true
控制台日志成果
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.6.9)
... ...
2023-04-17 14:17:35.172 INFO 25577 --- [ main] c.test.selfcoding.SelfCodingApplication : No active profile set, falling back to 1 default profile: "default"
2023-04-17 14:17:35.771 INFO 25577 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8001 (http)
2023-04-17 14:17:35.777 INFO 25577 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-04-17 14:17:35.777 INFO 25577 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.64]
2023-04-17 14:17:35.859 INFO 25577 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-04-17 14:17:35.859 INFO 25577 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 655 ms
2023-04-17 14:17:35.899 INFO 25577 --- [ main] c.test.selfcoding.config.BeanConfigTest : ========person bean init========
2023-04-17 14:17:36.134 INFO 25577 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8001 (http) with context path ''
2023-04-17 14:17:36.141 INFO 25577 --- [ main] c.test.selfcoding.SelfCodingApplication : Started SelfCodingApplication in 1.421 seconds (JVM running for 1.775)
能够看到打印了========person bean init========日志，类收效。
@ConditionalOnExpression
介绍
- 上述讲解的
@ConditionalOnProperty只能精准的匹配havingValue中的值进行控制，无法依据更多的特点值进行匹配（即使它有数组的value值，也只能配合havingValue进行与校验） - 咱们能够经过
@ConditionalOnExpression注解进行其他特点值的表达式来校验。 -
@ConditionalOnExpression是执行Spel表达式，依据返回的布尔值判别是否契合条件。
源码
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//
package org.springframework.boot.autoconfigure.condition;
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.context.annotation.Conditional;
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
@Documented
@Conditional({OnExpressionCondition.class})
public @interface ConditionalOnExpression {
//Spel表达式
String value() default "true";
}
运用示例
需测验的注解类一
/**
* @Description 测验bean装备
* @Author LiaoJy
* @Date 2023/4/17
*/
@Slf4j
@Configuration
//@ConditionalOnProperty(prefix = "conditional", name = "configuration.switch", havingValue = "true", matchIfMissing = true)
@ConditionalOnExpression("!'${conditional.configuration.switch}'.equals('false')")
public class BeanConfigTest {
@Bean
public PersonBean personBean() {
PersonBean personBean = new PersonBean();
personBean.setAge(30);
personBean.setName("andya");
log.info("========person bean init========");
return personBean;
}
}
此刻只需装备conditional.configuration.switch不为false值，此类都会收效。
需测验的注解类二
/**
* @Description 测验bean装备
* @Author LiaoJy
* @Date 2023/4/17
*/
@Slf4j
@Configuration
//@ConditionalOnProperty(prefix = "conditional", name = "configuration.switch", havingValue = "true", matchIfMissing = true)
@ConditionalOnExpression("${conditional.configuration.switch:true}")
public class BeanConfigTest {
@Bean
public PersonBean personBean() {
PersonBean personBean = new PersonBean();
personBean.setAge(30);
personBean.setName("andya");
log.info("========person bean init========");
return personBean;
}
}
此刻只要装备conditional.configuration.switch为false值，此类才不会收效。
其他运用场景示例
- 布尔特点
@ConditionalOnExpression("${conditional.configuration.switch:true}
- 多个布尔特点，只需满意其一
@ConditionalOnExpression("${conditional.configuration.switch1:true} || ${conditional.configuration.switch2:true}")
- 装备值等于数字
@ConditionalOnExpression("${conditional.configuration.switch} == 1")
@ConditionalOnExpression("${conditional.configuration.switch} != 1")
- 装备值与指定字符串相同
@ConditionalOnExpression("'${conditional.configuration.switch}'.equals('yes')")
- 多个装备值相同
@ConditionalOnExpression("'${conditional.configuration.str1}'.equals('${conditional.configuration.str2}')")
- … …
总结
原本只想用用@ConditionalOnProperty，用完@ConditionalOnExpression更爽一些！
