使用Spring @DependsOn控制bean加載前後順序

經常遇到加載A類bean時，裏面方法依賴B類bean。但是A類比B類先加載，導致B類對象爲空。

方法一，也是比較常用的使用@Order註解

@Component
@Order(-1)
public class A implements Ordered {

    /**
     * 設置加載順序
     * @return
     */
    @Override
    public int getOrder() {
        return 0;
    }
}

 

方法二

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

import java.lang.annotation.Annotation;
import java.util.Map;

/**
 * ApplicationContextAware實現類，用於獲取當前的Spring容器
 * 註解不能少
 */
@Component
public class SpringUtils implements ApplicationContextAware {
    private static ApplicationContext applicationContext;

    private static final Logger logger = LoggerFactory.getLogger(SpringUtils.class);

    /**
     * Spring容器會在創建該Bean之後，自動調用該Bean的setApplicationContext方法
     * @param applicationContext
     */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        if(SpringUtils.applicationContext == null) {
            SpringUtils.applicationContext = applicationContext;
        }
    }

    /**
     * 獲取applicationContext
     * @return
     */
    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    /**
     * 通過name獲取 Bean.
     * @param name
     * @return
     */
    public static Object getBean(String name){
        return getApplicationContext().getBean(name);
    }

    /**
     * 通過class獲取Bean.
     * @param clazz
     * @param <T>
     * @return
     */
    public static <T> T getBean(Class<T> clazz){
        return getApplicationContext().getBean(clazz);
    }

    /**
     * 通過name,以及Clazz返回指定的Bean
     * @param name
     * @param clazz
     * @param <T>
     * @return
     */
    public static <T> T getBean(String name,Class<T> clazz){
        return getApplicationContext().getBean(name, clazz);
    }

    /**
     * 通過註解獲取Bean集合
     * @param annotationType
     * @return
     */
    public static Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType){
        return getApplicationContext().getBeansWithAnnotation(annotationType);
    }
}

 

例如A類裏面用到springUtils的bean名

@Component
@DependsOn(value = "springUtils")
public class A {
}