@Configuration 相关依赖注入问题

用户8889406

发布于 2023-03-05 15:32:15

7150

发布于 2023-03-05 15:32:15

文章被收录于专栏：小呙同学

出现的问题

问题的原因

项目集成了es，在项目中写了一个ElasticSearchClientConfig类，需要该类中创建RestHighLevelClient的实例对象。需要配置es的ip地址和port端口号，但是不能在代码中写死，这样就不够灵活和优雅了,于是我在PropertiesConfig类中添加了es相关的属性，并且将对应的值配置到了nacos配置中心上，通过@Value来获取对应的值，这样就会灵活优雅很多。

当我将代码修改后，重启服务后，发现获取不到对应的值。

import com.shlz.common.utils.PropertiesConfig;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

import javax.annotation.PostConstruct;

/**
 * ElasticSearch客户端配置
 *
 * @author xGuo
 * @date 2022/07/19
 */
@Configuration
public class ElasticSearchClientConfig {

    @Bean
    public RestHighLevelClient restHighLevelClient() {

        System.out.println("ElasticSearchClientConfig 获取属性值...");
        System.out.println(PropertiesConfig.ES_IP);
        System.out.println(PropertiesConfig.ES_PORT);
        System.out.println("ElasticSearchClientConfig 获取属性值结束...");
        return new RestHighLevelClient(
                RestClient.builder(new HttpHost(PropertiesConfig.ES_IP, 
                         PropertiesConfig.ES_PORT, "http")));
    }
}

控制台打印

Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.elasticsearch.client.RestHighLevelClient]: Factory method ‘restHighLevelClient’ threw exception; nested exception is java.lang.NullPointerException at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:653) … 35 common frames omitted
Caused by: java.lang.NullPointerException: null at com.shlz.common.config.ElasticSearchClientConfig.restHighLevelClient(ElasticSearchClientConfig.java:53) ====> ** 就是 return new RestHighLevelClient(…) 这行代码 ** at com.shlz.common.config.ElasticSearchClientConfig

restHighLevelClient1(<generated>)atcom.shlz.common.config.ElasticSearchClientConfig1(<generated>) at com.shlz.common.config.ElasticSearchClientConfig1(<generated>)atcom.shlz.common.config.ElasticSearchClientConfigEnhancerBySpringCGLIBEnhancerBySpringCGLIBEnhancerBySpringCGLIB3124811c3124811c3124811cFastClassBySpringCGLIBFastClassBySpringCGLIBFastClassBySpringCGLIBa8645581.invoke(<generated>)atorg.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244)atorg.springframework.context.annotation.ConfigurationClassEnhancera8645581.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) at org.springframework.context.annotation.ConfigurationClassEnhancera8645581.invoke(<generated>)atorg.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244)atorg.springframework.context.annotation.ConfigurationClassEnhancerBeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331) at com.shlz.common.config.ElasticSearchClientConfig

解决方式

原来我以为是修饰了@Configuration类无法引用另外一个修饰了@Configuration类中的属性，后面发现只是使用static姿势不对的问题。

尝试处理一：

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class PropertiesConfig {
  
  	@Value("${es.ip}")
    public  String ES_IP;
  
    @Value("${es.port}")
    public  Integer ES_PORT;
}

发现直接在ElasticSearchClientConfig中进行依赖注入，然后调用属性值，是可以获取到nacos配置中心的值。

import com.shlz.common.utils.PropertiesConfig;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * ElasticSearch客户端配置
 *
 * @author xGuo
 * @date 2022/07/19
 */
@Configuration
public class ElasticSearchClientConfig {

    @Autowired
    PropertiesConfig propertiesConfig;

    @Bean
    public RestHighLevelClient restHighLevelClient() {
        return new RestHighLevelClient(
                RestClient.builder(new HttpHost(propertiesConfig.ES_IP, propertiesConfig.ES_PORT, "http")));
    }
}

尝试处理二：

PropertiesConfig类不做改动，在ElasticSearchClientConfig做处理，使用@PostConstruct注释添加一个初始化方法来获取值。发现是可以获取到的。

import com.shlz.common.utils.PropertiesConfig;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

/**
 * ElasticSearch客户端配置
 *
 * @author xGuo
 * @date 2022/07/19
 */
@Configuration
public class ElasticSearchClientConfig {
    @Autowired
    PropertiesConfig propertiesConfig;
    
    private static String ip;
    private static Integer port;
    
    @PostConstruct
    public void init(){
        ip = PropertiesConfig.ES_IP;
        port = PropertiesConfig.ES_PORT;
    }

    @Bean
    public RestHighLevelClient restHighLevelClient() {
        return new RestHighLevelClient(
                RestClient.builder(new HttpHost(ip,port, "http")));
    }
}

@PostConstruct详解

@PostConstruct注解好多人以为是Spring提供的。其实是Java自己的注解。 Java中该注解的说明：@PostConstruct该注解被用来修饰一个非静态的void（）方法。被@PostConstruct修饰的方法会在服务器加载Servlet的时候运行，并且只会被服务器执行一次。PostConstruct在构造函数之后执行，init（）方法之前执行。通常我们会是在Spring框架中使用到@PostConstruct注解该注解的方法在整个Bean初始化中的执行顺序： Constructor(构造方法) -> @Autowired(依赖注入) -> @PostConstruct(注释的方法) 应用：在静态方法中调用依赖注入的Bean中的方法。