Spring Boot2.x-06Spring Boot基礎-使用@Conditional註解根據特定的條件裝配bean
阿新 • • 發佈:2018-12-17
概述
假設在某些特定的場景下,希望根據特定的條件去載入某個或某些bean,我們可以使用@Condtional註解, Spring 4.0的時候加入的這個註解。
例子
假設,我們在配置了資料庫的幾個屬性時,才去例項化bean,否則不初始化這個bean。這個例子可能不太合適,權當理解這個註解的用法了
Step1 實現Condition介面,重寫matches方法
package com.artisan.springbootmaster.conditional;
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 DatabaseCondtional implements Condition {
/**
* 資料庫bean的裝配條件
*
* @param context 上下文
* @param metadata 註釋型別的元資料
* @return true 裝配Bean ,否則不裝配
*/
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
// 根據context取出對應的Env資訊
Environment environment = context.getEnvironment();
// 判斷屬性檔案是否存在對應的資料庫配置
return environment.containsProperty("datasource.driverName")
&& environment.containsProperty("datasource.url")
&& environment.containsProperty("datasource.username")
&& environment.containsProperty("datasource.password");
}
}
Step2 在對應的@Bean上使用@Conditional註解
package com.artisan.springbootmaster.conditional;
import org.apache.commons.dbcp2.BasicDataSourceFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.*;
import javax.sql.DataSource;
import java.util.Properties;
@Configuration
@PropertySource(value = "classpath:jdbc.properties",ignoreResourceNotFound = true)
public class Config {
@Bean(name = "datasource" ,destroyMethod = "close")
@Conditional(DatabaseCondtional.class)
public DataSource initDataSource(
@Value("${datasource.driverName}") String driver,
@Value("${datasource.url}") String url,
@Value("${datasource.username}") String username,
@Value("${datasource.password}") String password){
System.out.println("driver:" + driver + "\n url:" + url+ "\n username:" + username
+ "\n password:" + password) ;
Properties properties = new Properties();
properties.setProperty("driver",driver);
properties.setProperty("url",url);
properties.setProperty("username",username);
properties.setProperty("password",password);
DataSource dataSource = null;
try {
dataSource = BasicDataSourceFactory.createDataSource(properties);
} catch (Exception e) {
e.printStackTrace();
}
return dataSource;
}
}
測試
package com.artisan.springbootmaster.conditional;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import javax.sql.DataSource;
public class Test {
public static void main(String[] args){
ApplicationContext ctx = new AnnotationConfigApplicationContext(Config.class);
//DataSource dataSource = (DataSource) ctx.getBean("datasource");
DataSource dataSource = ctx.getBean(DataSource.class);
System.out.println("datasource:" + dataSource);
}
}
結果
當我們修改掉某個屬性後,DatabaseCondtional#matches方法肯定返回false, 按照推測,該bean不會被載入到IoC容器中,我們來驗證下
將 datasource.driverName 改為 datasource.driverName1
重新測試,丟擲了異常。
因為我們在獲取bean的時候,IoC容器中並不存在該bean。