SpringBoot中的Condition包下常用条件依赖注解案例介绍

一、@ConditionalOnClass() Spring中存在指定class对象时，注入指定配置

和ConditionalOnBean()的区别在于ConditionalOnBean()是根据ioc里是否有此实例对象，而ConditionalOnClass()表示只要在Spring中有这个类就可以

1.首先引入pom依赖

<!--引入springboot父依赖-->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.2.RELEASE</version>
</parent>
<dependencies>
    <!--引入启动器依赖-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
<!--用json来判断是否创建bean-->
	<dependency>
   		<groupId>com.alibaba</groupId>
   	 	<artifactId>fastjson</artifactId>
   		<version>1.2.71</version>
	</dependency>
</dependencies>

2.实体类测试对象

根据Condition返回结果表示是否将此对象注入ioc中; true:表示注入ioc

//根据Condition返回结果表示是否注入ioc中true：表示注入ioc
public class Student {
    String name="小白";
    Integer age =12;
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

3.定义@ConditionalOnClass（）配置类

name = "com.alibaba.fastjson.JSON" 表示此spring中是否有这个类，有的话就注入此配置到ioc

import com.it.mhh.entry.Student;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class CustomConditionOnClass {
    @Bean
    @ConditionalOnClass(name = "com.alibaba.fastjson.JSON")
    //这里就是判断是否吧此对象注入IOC，ClassCondition此类matches对象的返回的Boolean[true：创建，false：不创建]
    public Student getStudent() {
        return new Student();
    }
}

4.启动类测试

@ConditionalOnClass() Spring中存在指定class，对应该配置才会生效

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
//@ConditionalOnClass() Spring中存在指定class，对应该配置才会生效
@SpringBootApplication
public class ConditionApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(ConditionApplication.class, args);
        //Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'getStudent' available[表示没有获取到这个bean]
        Object getStudent = run.getBean("getStudent");//这里因为是注入ioc时 @Bean没有指定名字，则就是方法名从ioc中获取此对象
        System.out.println(getStudent); //Student{name='小白', age=12}
    }
}

二、注入指定配置

@ConditionalOnMissingClass() Spring中不存在指定class对象时，注入指定配置

和ConditionalOnMissingBean()的区别在于ConditionalOnMissingBean()是根据ioc里没有此实例对象，而ConditionalOnClass()表示只要在Spring中没有这个类就可以

1.首先引入pom依赖

<!--引入springboot父依赖-->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.2.RELEASE</version>
</parent>
<dependencies>
    <!--引入启动器依赖-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
<!--用json来判断是否创建bean-->
<!--<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.71</version>
</dependency>-->
</dependencies>

2.实体类测试对象

根据Condition返回结果表示是否将此对象注入ioc中; true:表示注入ioc

//根据Condition返回结果表示是否注入ioc中true：表示注入ioc
public class Student {
    String name="小白";
    Integer age =12;
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

3.定义@ConditionalOnMissingClass（）配置类

name = "com.alibaba.fastjson.JSON" 表示此spring中是否有这个类，有的话就==不==注入此配置到ioc

import com.it.mhh.entry.Student;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class CustomConditionOnMissingClass {
    @Bean
    @ConditionalOnMissingClass("com.alibaba.fastjson.JSON")
    //这里就是判断是否吧此对象注入IOC，ClassCondition此类matches对象的返回的Boolean[true：创建，false：不创建]
    public Student getStudent() {
        return new Student();
    }
}

4.启动类测试

@ConditionalOnMissingClass Spring容器中==不存在==指定class，注入指定配置

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
//@ConditionalOnMissingClass Spring容器中不存在指定class，注入指定配置
@SpringBootApplication
public class ConditionApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(ConditionApplication.class, args);
        //Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'getStudent' available[表示没有获取到这个bean]
        Object getStudent = run.getBean("getStudent");//这里因为是注入ioc时 @Bean没有指定名字，则就是方法名从ioc中获取此对象
        System.out.println(getStudent); //Student{name='小白', age=12}
    }
}

三、加载指定配置

@ConditionalOnBean() 根据ioc中判断有没有此实例对象,有则加载指定配置

和ConditionalOnClass()的区别在于ConditionalOnClass()是根据Spring中是否有此类，而ConditionalOnBean()表示在ioc中是否由此实例对象；

1.首先引入pom依赖

<!--引入springboot父依赖-->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.2.RELEASE</version>
</parent>
<dependencies>
    <!--引入启动器依赖-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

2.实体类测试对象

根据Condition返回结果表示是否将此对象注入ioc中; true:表示注入ioc

//根据Condition返回结果表示是否注入ioc中true：表示注入ioc
public class Student {
    String name="小白";
    Integer age =12;
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

2.1 引入条件判断实体类

将此类==注入==ioc容器

importorg.springframework.stereotype.Component;
@Component
Public class BeanServer{
}

3.定义@ConditionalOnBean（）配置类

BeanServer.class :判断ioc中是否有此类对象，==有==的话就加载此配置

import com.it.mhh.customConditionOnBeanOrOnMissingBean.server.TestServer;
import com.it.mhh.entry.Student;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class CustomConditionOnBean {
    @Bean
    @ConditionalOnBean(BeanServer.class)
    //这里就是判断是否吧此对象注入IOC，ClassCondition此类matches对象的返回的Boolean[true：创建，false：不创建]
    public Student getStudent() {
        return new Student();
    }
}

4.启动类测试

@ConditionalOnBean() Spring容器中==存在==指定class实例对象时，注入指定配置

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
//@ConditionalOnBean() Spring容器中存在指定class实例对象时，注入指定配置
@SpringBootApplication
public class ConditionApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(ConditionApplication.class, args);
        //Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'getStudent' available[表示没有获取到这个bean]
        Object getStudent = run.getBean("getStudent");//这里因为是注入ioc时 @Bean没有指定名字，则就是方法名从ioc中获取此对象
        System.out.println(getStudent); //Student{name='小白', age=12}
    }
}

四、ioc中判断

ConditionalOnMissingBean() 根据ioc中判断有没有此实例对象,没有则加载指定配置

和ConditionalOnMissingClass()的区别在于ConditionalOnMissingClass()是根据Spring中是否有此类，而ConditionalOMissingnBean()表示在ioc中是否由此实例对象；

1.首先引入pom依赖

<!--引入springboot父依赖-->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.2.RELEASE</version>
</parent>
<dependencies>
    <!--引入启动器依赖-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

2.实体类测试对象

根据Condition返回结果表示是否将此对象注入ioc中; true:表示注入ioc

//根据Condition返回结果表示是否注入ioc中true：表示注入ioc
public class Student {
    String name="小白";
    Integer age =12;
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

2.1 引入条件判断实体类

==不注入==此类到ioc容器

importorg.springframework.stereotype.Component;
//@Component
Public class BeanServer{
}

3.定义@ConditionalOnMissingBean（）配置类

BeanServer.class :判断ioc中是否有此类对象，==没有==的话就加载此配置

import com.it.mhh.customConditionOnBeanOrOnMissingBean.server.TestServer;
import com.it.mhh.entry.Student;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
//@Configuration
public class CustomConditionOnMissingBean {

    @Bean
    @ConditionalOnMissingBean(BeanServer.class)
    //这里就是判断是否吧此对象注入IOC，ClassCondition此类matches对象的返回的Boolean[true：创建，false：不创建]
    public Student getStudent() {
        return new Student();
    }
}

4.启动类测试

@ConditionalOnMissingBean() Spring ioc中不存在指定class实例对象时，注入指定配置

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
//@ConditionalOnMissingBean() Spring容器中不存在指定class实例对象时，注入指定配置
@SpringBootApplication
public class ConditionApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(ConditionApplication.class, args);
        //Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'getStudent' available[表示没有获取到这个bean]
        Object getStudent = run.getBean("getStudent");//这里因为是注入ioc时 @Bean没有指定名字，则就是方法名从ioc中获取此对象
        System.out.println(getStudent); //Student{name='小白', age=12}
    }
}

五、@ConditionalOnProperty()加载配置

@ConditionalOnProperty() 配置文件中配置的指定参数值符合要求时，加载此配置

与@ConditionalOnExpression()的区别在于@ConditionalOnProperty() 注解使用的是通过注解中的属性赋值作为参照物和yml里的配置进行匹配是否为相同；

1.首先引入pom依赖

<!--引入springboot父依赖-->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.2.RELEASE</version>
</parent>
<dependencies>
    <!--引入启动器依赖-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

2.实体类测试对象

根据Condition返回结果表示是否将此对象注入ioc中; true:表示注入ioc

//根据Condition返回结果表示是否注入ioc中true：表示注入ioc
public class Student {
    String name="小白";
    Integer age =12;
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

3.定义@ConditionalOnProperty() 配置类

prefix = "class",name = "teacher",matchIfMissing=false, havingValue = "小黑"
==@ConditionalOnProperty()中属性含义==
public @interface ConditionalOnProperty {String[] value() default {}; // 数组，获取对应yml名称的key，与name含义一样，不能同时使用value和name;

??String prefix() default ""; //配置文件中yml名称的前缀;String[] name() default {};// 数组，获取对应yml名称的key，与value含义一样，不能同时使用value和name;String havingValue() default ""; //配置文件yml的value值boolean matchIfMissing() default false; //配置文件yml中没有与之匹配到的数值，是否加载，true：表示正常加载此配置，false表示如果yml中没有此数值就不加载；}

import com.it.mhh.entry.Student;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class CustomConditionOnProperty {
    @Bean
    @ConditionalOnProperty(prefix = "class",name = "teacher",matchIfMissing=false, havingValue = "小黑")
    //这里就是判断是否吧此对象注入IOC，ClassCondition此类matches对象的返回的Boolean[true：创建，false：不创建]
    public Student getStudent() {
        return new Student();
    }
}

4.application.yml配置

@ConditionalOnProperty()注解中的 prefix 属性就是此yml配的前缀 yml，name就是 teacher，而havingValue 则就是'小黑'，如果application中有此配置，则加载相应配置

class:
  teacher: 小黑

5.启动类测试

@ConditionalOnProperty()配置文件中配置的指定参数值符合要求时，加载此配置

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
// @ConditionalOnProperty()配置文件中配置的指定参数值符合要求时，加载此配置
@SpringBootApplication
public class ConditionApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(ConditionApplication.class, args);
        //Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'getStudent' available[表示没有获取到这个bean]
        Object getStudent = run.getBean("getStudent");//这里因为是注入ioc时 @Bean没有指定名字，则就是方法名从ioc中获取此对象
        System.out.println(getStudent); //Student{name='小白', age=12}
    }
}

六、@ConditionalOnExpression() 配置文件

@ConditionalOnExpression() 配置文件中配置的指定参数值与我给的值比较为true时，加载此配置

与@ConditionalOnProperty() 的区别在于@ConditionalOnExpression()注解使用的是SpringEL表达式与我给的值进行匹配，为true时加载配置,而@ConditionalOnProperty() 注解使用的是通过注解中的属性赋值作为参照物和yml里的配置进行匹配是否为相同；

1.首先引入pom依赖

<!--引入springboot父依赖-->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.2.RELEASE</version>
</parent>
<dependencies>
    <!--引入启动器依赖-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

2.实体类测试对象

根据Condition返回结果表示是否将此对象注入ioc中; true:表示注入ioc

//根据Condition返回结果表示是否注入ioc中true：表示注入ioc
public class Student {
    String name="小白";
    Integer age =12;
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

3.定义@ConditionalOnExpression() 配置类

"'${class.teacher}'.equals('小黑')" :Spring EL表达式，配置文件class.teacher里对应的值去比较我输入的’小黑‘是否相同，true:加载此配置；

import com.it.mhh.entry.Student;
import org.springframework.boot.autoconfigure.condition.ConditionalOnExpression;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class CustomConditionOnExpression {
    @Bean
    //配置文件中配置的指定参数值与我要做比较的值为true时，加载此配置
    @ConditionalOnExpression("'${class.teacher}'.equals('小黑')")
    //这里就是判断是否吧此对象注入IOC，ClassCondition此类matches对象的返回的Boolean[true：创建，false：不创建]
    public Student getStudent() {
        return new Student();
    }
}

4.application.yml配置

@ConditionalOnExpression()注解 value属性就是此配置的键 class.teacherg 而获取到的值就是’小黑‘，然后进行比较， true则加载相应配置

class:
  teacher: 小黑

5.启动类测试

@ConditionalOnExpression()//配置文件中配置的指定参数值与我传的参数进行比较，如果相同则为true，加载此配置，否则不加载

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
// @ConditionalOnExpression()//配置文件中配置的指定参数值与我传的参数比较，相同为true时，加载此配置
@SpringBootApplication
public class ConditionApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(ConditionApplication.class, args);
        //Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'getStudent' available[表示没有获取到这个bean]
        Object getStudent = run.getBean("getStudent");//这里因为是注入ioc时 @Bean没有指定名字，则就是方法名从ioc中获取此对象
        System.out.println(getStudent);
    }
}

七、@ConditionalOnResource() 指定的资源文件出现在classpath中生效

(就是编译后target里classes里的路径名是否存在)

指定文件路径名存在时，对应配置生效

1.首先引入pom依赖

<!--引入springboot父依赖-->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.2.RELEASE</version>
</parent>
<dependencies>
    <!--引入启动器依赖-->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

2.实体类测试对象

根据Condition返回结果表示是否将此对象注入ioc中; true:表示注入ioc

//根据Condition返回结果表示是否注入ioc中true：表示注入ioc
public class Student {
    String name="小白";
    Integer age =12;
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

3.定义@ConditionalOnResource()配置类

resources = "com\it\mhh" :编译后taget->classes里的路径名是否存在，存在为true，加载配置

import com.it.mhh.entry.Student;
import org.springframework.boot.autoconfigure.condition.ConditionalOnResource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class CustomConditionOnResource {
    @Bean
    //指定的资源文件出现在classpath中生效(就数编译后target里classes里的包路径)
    @ConditionalOnResource(resources = "com\\it\\mhh")
    //这里就是判断是否吧此对象注入IOC，ClassCondition此类matches对象的返回的Boolean[true：创建，false：不创建]
    public Student getStudent() {
        return new Student();
    }
}

4.启动类测试

@ConditionalOnResource()//指定的资源文件出现在classpath中生效(就数编译后target里classes里的包路径)

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
@SpringBootApplication
//@ConditionalOnResource()//指定的资源文件出现在classpath中生效(就数编译后target里classes里的包路径)
public class ConditionApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(ConditionApplication.class, args);
        //Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'getStudent' available[表示没有获取到这个bean]
        Object getStudent = run.getBean("getStudent");//这里因为是注入ioc时 @Bean没有指定名字，则就是方法名从ioc中获取此对象
        System.out.println(getStudent);
    }
}

SpringBoot中的Condition包下常用条件依赖注解案例介绍

目录

一、@ConditionalOnClass() Spring中存在指定class对象时，注入指定配置

1.首先引入pom依赖

2.实体类测试对象

3.定义@ConditionalOnClass（）配置类

4.启动类测试

二、注入指定配置

1.首先引入pom依赖

2.实体类测试对象

3.定义@ConditionalOnMissingClass（）配置类

4.启动类测试

三、加载指定配置

1.首先引入pom依赖

2.实体类测试对象

2.1 引入条件判断实体类

3.定义@ConditionalOnBean（）配置类

4.启动类测试

四、ioc中判断

1.首先引入pom依赖

2.实体类测试对象

2.1 引入条件判断实体类

3.定义@ConditionalOnMissingBean（）配置类

4.启动类测试

五、@ConditionalOnProperty()加载配置

1.首先引入pom依赖

2.实体类测试对象

3.定义@ConditionalOnProperty() 配置类

4.application.yml配置

5.启动类测试

六、@ConditionalOnExpression() 配置文件

1.首先引入pom依赖

2.实体类测试对象

3.定义@ConditionalOnExpression() 配置类

4.application.yml配置

5.启动类测试

七、@ConditionalOnResource() 指定的资源文件出现在classpath中生效

1.首先引入pom依赖

2.实体类测试对象

3.定义@ConditionalOnResource()配置类

4.启动类测试

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