SpringBoot-----SpringBoot @Conditional注解自动配置报告

一、@Conditional简介

@Conditional是Spring4新提供的注解，它的作用是按照一定的条件进行判断，满足条件给容器注册Bean。SpringBoot是根据配置文件的内容决定是否创建Bean，以及如何创建bean到Spring容器中，而Spring Boot自动化配置的核心控制，就是@Conditional注解。

二、@ConditionalOnXX注解

@ConditionalOnXX注解被定义在org.springframework.boot.autoconfigure包下面的condition文件夹下，它是一种条件装配，满足Conditional指定的条件，则进行组件注入

在ideal中使用ctrl+H可以看到@Conditional的根注解和派生注解，这个根注解下派生了很多派生注解

@Conditional扩展注解	作用（判断是否满足当前指定条件）
@ConditionalOnJava	系统的java版本是否符合要求
@ConditionalOnBean	容器中存在指定Bean
@ConditionalOnMissingBean	容器中不存在指定Bean
@ConditionalOnExpression	满足SpEL表达式指定
@ConditionalOnClass	系统中有指定的类
@ConditionalOnMissingClass	系统中没有指定的类
@ConditionalOnSingleCandidate	容器中只有一个指定的Bean，或者这个Bean是首选Bean
@ConditionalOnProperty	系统中指定的属性是否有指定的值
@ConditionalOnResource	路径下是否存在指定资源文件
@ConditionalOnWebApplication	当前是web环境
@ConditionalOnNotWebApplication	当前不是web环境
@ConditionalOnJndi	JNDI存在指定项

举例说明：

一、加载2个Bean

1、新建一个BeanConfig.java，利用@Configuration+@Bean加载2个Bean

package com.zk.autoconfigdemo;
 
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
 
@Configuration
public class BeanConfig {
    /*
     *如果windowsCondition的实现方法返回true,则注入这个bean
     */
    @Bean
    public Person person1(){
        return  new Person("BillGates",62);
    }
    /**
     * 如果LinuxCondition的实现方法返回true,则注入这个Bean
     */
    @Bean
    public Person person2(){
        return  new Person("Linus",50);
    }
}　

2、新建一个Person.java类

package com.zk.autoconfigdemo;
 
public class Person {
    private String name;
    private Integer age;
 
    public Person(String name, int age) {
        this.name=name;
        this.age=age;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
 
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

3、测试是否都加载到Spring容器中

　AutoconfigdemoApplication.java

package com.zk.autoconfigdemo;
 
import org.apache.catalina.core.ApplicationContext;
import org.springframework.beans.factory.annotation.Configurable;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
 
import java.util.Map;
 
@SpringBootApplication
public class AutoconfigdemoApplication {
 
    public static void main(String[] args) {
        ConfigurableApplicationContext run=SpringApplication.run(AutoconfigdemoApplication.class,args);
        Map<String,Person> personMap=run.getBeansOfType(Person.class);
        System.out.println(personMap);
    }
 
}

　运行结果如下：

三、利用@Conditional根据条件加载Bean

1、创建条件判断的类

如果是Windows系统则加载Bean

WindowsCondition.java

package com.zk.autoconfigdemo;
 
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotatedTypeMetadata;
 
public class WindowsCondition implements Condition {
    /**
     *
     * @param context:判断条件能使用的上下文环境
     * @param metadata:注解所在位置的注释信息
     * @return
     */
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        //获取ioc使用的BeanFactory
        ConfigurableListableBeanFactory beanFactory=context.getBeanFactory();
        //获取类加载器
        ClassLoader classLoader=context.getClassLoader();
        //获取当前环境信息
        Environment environment=context.getEnvironment();
        //获取bean定义的注册类
        BeanDefinitionRegistry registry=context.getRegistry();
 
        //获取当前系统名
        String property=environment.getProperty("os.name");
        //包含windows说明是windows系统，返回true
        if(property.contains("Windows")){
            return true;
        }
        return false;
    }
}

如果是Linux系统则加载Bean

LinuxCondition.java

package com.zk.autoconfigdemo;
 
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotatedTypeMetadata;
 
public class LinuxCondition implements Condition{
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        Environment environment=context.getEnvironment();
 
        String property = environment.getProperty("os.name");
        if(property.contains("Linux")){
            return true;
        }
        return false;
    }
}

2、将@Conditional放在方法上

BeanConfig.java

package com.zk.autoconfigdemo;
 
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
 
@Configuration
public class BeanConfig {
    /*
     *如果windowsCondition的实现方法返回true,则注入这个bean
     */
    @Bean
    @Conditional(WindowsCondition.class)
    public Person person1(){
        return  new Person("BillGates",62);
    }
    /**
     * 如果LinuxCondition的实现方法返回true,则注入这个Bean
     */
    @Bean
    @Conditional(LinuxCondition.class)
    public Person person2(){
        return  new Person("Linus",50);
    }
}

运行AutoconfigdemoApplication.java

package com.zk.autoconfigdemo;
 
import org.apache.catalina.core.ApplicationContext;
import org.springframework.beans.factory.annotation.Configurable;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
 
import java.util.Map;
 
@SpringBootApplication
public class AutoconfigdemoApplication {
 
    public static void main(String[] args) {
        ConfigurableApplicationContext run=SpringApplication.run(AutoconfigdemoApplication.class,args);
        Map<String,Person> personMap=run.getBeansOfType(Person.class);
        System.out.println(personMap);
    }
 
}

　得到的结果如下：

因为当前系统为windows，所以只返回一个值。

3、将@Conditional注解放在类上

BeanConfig.java

package com.zk.autoconfigdemo;
 
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
 
@Configuration
@Conditional(WindowsCondition.class)
public class BeanConfig {
    /*
     *如果windowsCondition的实现方法返回true,则注入这个bean
     */
    @Bean
    public Person person1(){
        return  new Person("BillGates",62);
    }
    /**
     * 如果LinuxCondition的实现方法返回true,则注入这个Bean
     */
    @Bean
    public Person person2(){
        return  new Person("Linus",50);
    }
}

因为所运行的设备为windows10，所以@Conditional(WindowsCondition.class) 生效可用，运行结果如下：

4、@Conditional传多个条件，是且关系

@Conditional接受一个Class数组，可以传多个条件，当所有条件都是true时，才生效。

可想项目的代码是不会加载Person对象的，因为

WindowsCondition.class返回true，LinuxCondition.class返回false，所以MyBeanConfig整个类失效，不能加载它下面的Bean。

@Configuration
@Conditional({WindowsCondition.class, LinuxCondition.class})
public class MyBeanConfig {
 
    @Bean
    //@Conditional(WindowsCondition.class)
    public Person person1(){
        return new Person("Bill Gates", 66);
    }
 
    @Bean
    //@Conditional(LinuxCondition.class)
    public Person person2(){
        return new Person("Linus", 50);
    }
}