Spring @Autowired 字段为空？

Question

为什么我将 Spring @Autowired 字段设为 null ：

Exception : 
    java.lang.NullPointerException
        at com.elastic.controller.MainController.getUsers(MainController.java:38)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

---

MainController.java

package com.elastic.controller;

        @Component()
        @Path("/user")
        public class MainController {


            @Autowired
            private ElasticSearchRepository elasticSearchRepository;

            @GET
            @Path("/getAllUsers")
            @Produces(MediaType.APPLICATION_JSON)
            public Response getUsers() throws Exception{

                List<User> userlist =new ArrayList<User>();
                Iterator<User> users = elasticSearchRepository.getAllUsers();

                while (users.hasNext()) {
                    userlist.add(users.next());
                }       

                return Response.ok(userlist).build();

            }

        }

---

ElasticSearchRepository.java

package com.elastic.repository;
@Configuration
@EnableElasticsearchRepositories(basePackages = "com.elastic.repository")
public class ElasticSearchRepository {

public Iterator<User> getAllUsers() {
    Iterator<User> users = userRepository.findAll().iterator();
    return users;
}

}

---

mvc-dispatcher-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
            <beans xmlns="http://www.springframework.org/schema/beans"
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc"      
                   xmlns:context="http://www.springframework.org/schema/context"
                   xmlns:elasticsearch="http://www.springframework.org/schema/data/elasticsearch"
                   xsi:schemaLocation="http://www.springframework.org/schema/data/elasticsearch http://www.springframework.org/schema/data/elasticsearch/spring-elasticsearch-1.0.xsd
                    http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
                    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd 
                    http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">



                <context:annotation-config />

                <mvc:annotation-driven />
                <context:component-scan base-package="com.elastic" />
                <elasticsearch:repositories base-package="com.elastic.repository" />
                <elasticsearch:repositories base-package="com.elastic.entity" />


            </beans>

对于控制器，我保留了 @component 注释，对于存储库，我保留了 @Configuration 但仍然出现此异常。请帮忙。

Answer 1

根据问题陈述，我能够找到两个问题，解决方案如下：

请试试这个

1. 请在 ElasticSearchRepository.java 类中尝试 @ComponentScan(basePackages = { "com.elastic" })

2. @Component() 在 MainController.java 类中重命名为 @Controller

Answer 2

这可能是由于您使用MainController 的方式造成的，如果您的主控制器没有由spring 上下文初始化和配置，即您使用new 关键字创建了MainController 的实例。

其次，我在 ElasticSearchRepository 中没有看到 getAllUsers() 方法，只是想知道您的代码是如何编译的？