17.1 @Conditional
- @Conditional为按照条件配置spring的bean提供了支持,即满足某种条件下,怎么配置对应的bean;
- 应用场景
- 当某一个jar包在classpath中的时候,配置某几个bean;
- 当某一个bean配置好后,会自动配置一个特定的bean;
- 当某种环境变量被设置后,创建某个bean;
- @Conditional为敏捷开发所提倡的原则"习惯优于配置"提供了支持;
- @Conditional是Spring Boot快速开发框架实现"习惯优于配置"的核心技术;
17.2 示例
演示在windows和linux系统下,初始化不同的bean,windows和linux作为判断条件;
17.2.1 构造判断条件
条件的构造需要类实现Condition接口,并实现matches方法
- WindowsCondition
package com.wisely.conditional;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class WindowsCondition implements Condition {
public boolean matches(ConditionContext context,
AnnotatedTypeMetadata metadata) {
return context.getEnvironment().getProperty("os.name").contains("Windows");
}
}
- LinuxCondition
package com.wisely.conditional;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class LinuxCondition implements Condition {
public boolean matches(ConditionContext context,
AnnotatedTypeMetadata metadata) {
return context.getEnvironment().getProperty("os.name").contains("Linux");
}
}
17.2.2 编写不同条件下需要的bean
- 接口
package com.wisely.conditional;
public interface CommandService {
public String showListCommand();
}
- WindowsCommnadService
package com.wisely.conditional;
public class WindowsCommnadService implements CommandService {
public String showListCommand() {
return "dir";
}
}
- LinuxCommandService
package com.wisely.conditional;
public class LinuxCommandService implements CommandService {
public String showListCommand() {
return "ls";
}
}
17.2.3 编写配置类
package com.wisely.conditional;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
@Configuration
public class DemoConfig {
@Bean
@Conditional(WindowsCondition.class)
public CommandService commandService() {
return new WindowsCommnadService();
}
@Bean
@Conditional(LinuxCondition.class)
public CommandService linuxEmailerService() {
return new LinuxCommandService();
}
}
17.2.4 测试
- windows下
package com.wisely.conditional;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class Main {
public static void main(String[] args) {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext("com.wisely.conditional");
CommandService cs = context.getBean(CommandService.class);
System.out.println(cs.showListCommand());
context.close();
}
}
输出结果
dir
- Linux下(本例没有切换到linux,直接修改os.name为Linux)
package com.wisely.conditional;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class Main {
public static void main(String[] args) {
System.setProperty("os.name", "Linux");
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("com.wisely.conditional");
CommandService cs = context.getBean(CommandService.class);
System.out.println(cs.showListCommand());
context.close();
}
}
输出结果
ls