SpringBoot深入探究@Conditional条件装配的使用
目录
- 1.相关介绍
- 2.举例测试
- 1.指定组件不存在时
- 2.指定组件存在时
- 3.完整代码
1.相关介绍
@Conditional注解可以用在任何类型或者方法上面,通过@Conditional注解可以配置一些条件判断,当所有条件都满足的时候,被@Conditional标注的目标才会被spring容器处理。
比如可以通过@Conditional来控制bean是否需要注册,控制被@Configuration标注的配置类是需要需要被解析等。
Conditional相关的其它注解:
注解 | 描述 |
---|---|
@ConditionalOnBean | 在某个 bean 存在的时候 |
@ConditionalOnMissingBean | 在某个 bean 不存在的时候 |
@ConditionalOnClass | 当前 classPath 下可以找到某个 class 的时候 |
@ConditionalOnMissingClass | 当前 classPath 下无法找到某个 class 的时候 |
@ConditionalOnResource | 当前 classPath 下否存在某个资源文件的时候 |
@ConditionalOnProperty | 当前 JVM 包含某个属性值的时候 |
@ConditionalOnWebApplication | 当前 Spring context 是 web 应用程序的时候 |
@ConditionalOnJava | 在指定JDK版本的时候 |
@ConditionalOnExpression | 符合表达式的时候 |
@ConditionalOnJndi | JNDI存在该项的时候 |
2.举例测试
@ConditionalOnBean, 在某个 bean 存在的时候被标注的组件才被注册到IOC容器中
下面是其详细代码
@Target({ElementType.TYPE, ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Documented @Conditional({OnBeanCondition.class}) public @interface ConditionalOnBean { Class<?>[] value() default {}; String[] type() default {}; Class<? extends Annotation>[] annotation() default {}; String[] name() default {}; SearchStrategy search() default SearchStrategy.ALL; Class<?>[] parameterizedContainer() default {}; }
我们就拿它来测试一下
1.指定组件不存在时
MyConfig
package com.limi.config; import com.limi.entity.User; import org.springframework.boot.autoconfigure.condition.ConditionalOnBean; import org.springframework.context.annotation.*; @Configuration public class MyConfig { // @Bean // public User user01(){ // return new User(1, "andy", "123456"); // } @Bean @ConditionalOnBean(name = "user01") //当user01存在时才注册user02 public User user02(){ return new User(2, "bob", "666666"); } }
MainApplication
package com.limi; import com.limi.entity.User; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.ConfigurableApplicationContext; @SpringBootApplication public class MainApplication { public static void main(String[] args) { //1、返回我们IOC容器 ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args); if(run.containsBean("user01")) System.out.println((User)run.getBean("user01")); System.out.println("user01 不存在!\n"); if(run.containsBean("user02")) System.out.println((User)run.getBean("user02")); else System.out.println("user02 不存在!\n"); } }
运行结果
2.指定组件存在时
MyConfig
package com.limi.config; import com.limi.entity.User; import org.springframework.boot.autoconfigure.condition.ConditionalOnBean; import org.springframework.context.annotation.*; @Configuration public class MyConfig { @Bean public User user01(){ return new User(1, "andy", "123456"); @Bean @ConditionalOnBean(name = "user01") //当user01存在时才注册user02 public User user02(){ return new User(2, "bob", "666666"); } }
MainApplication
package com.limi; import com.limi.entity.User; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.ConfigurableApplicationContext; @SpringBootApplication public class MainApplication { public static void main(String[] args) { //1、返回我们IOC容器 ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args); if(run.containsBean("user01")) System.out.println((User)run.getBean("user01")); else System.out.println("user01 不存在!\n"); if(run.containsBean("user02")) System.out.println((User)run.getBean("user02")); else System.out.println("user02 不存在!\n"); } }
运行结果
3.完整代码
pom.xml
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.limi</groupId> <artifactId>springboot-test1</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.3.4.RELEASE</version> </parent> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> </dependencies> <!--打包插件, 使用它可以把项目打包为jar包--> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project>
User
package com.limi.entity; public class User { private Integer id; private String userName; private String passWord; public User(){} public User(Integer id, String userName, String passWord) { this.id = id; this.userName = userName; this.passWord = passWord; } @Override public String toString() { return "User{" + "id=" + id + ", userName='" + userName + '\'' + ", passWord='" + passWord + '\'' + '}'; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getPassWord() { return passWord; } public void setPassWord(String passWord) { this.passWord = passWord; } }
MyConfig
package com.limi.config; import com.limi.entity.User; import org.springframework.boot.autoconfigure.condition.ConditionalOnBean; import org.springframework.context.annotation.*; @Configuration public class MyConfig { @Bean public User user01(){ return new User(1, "andy", "123456"); } @Bean @ConditionalOnBean(name = "user01") //当user01存在时才注册user02 public User user02(){ return new User(2, "bob", "666666"); } }
MainApplication
package com.limi; import com.limi.entity.User; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.ConfigurableApplicationContext; @SpringBootApplication public class MainApplication { public static void main(String[] args) { //1、返回我们IOC容器 ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args); if(run.containsBean("user01")) System.out.println((User)run.getBean("user01")); else System.out.println("user01 不存在!\n"); if(run.containsBean("user02")) System.out.println((User)run.getBean("user02")); else System.out.println("user02 不存在!\n"); } }
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