java - 应用程序上下文+ Autowiring

Question

我编写了一个示例应用程序，我试图将我的 CustomerService bean Autowiring 到我的 Application.class 中以执行 System.out.println()

但是它抛出了一个异常，说工厂层次结构的根，我不明白为什么我不能这样做，除了使用注释代码检索 bean？

我的错误

Aug 03, 2014 9:52:42 PM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5f3d285f: startup date [Sun Aug 03 21:52:42 SGT 2014]; root of context hierarchy
Aug 03, 2014 9:52:42 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
Aug 03, 2014 9:52:43 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@25bcb56b: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,customerRepository,customerService,org.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor]; root of factory hierarchy
we are using constructor injection
Exception in thread "main" java.lang.NullPointerException
    at Application.print(Application.java:20)
    at Application.main(Application.java:30)

这是我的代码。

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.pluralsight.service.CustomerService;


public class Application {
    @Autowired
    private CustomerService service;

    public Application(CustomerService service) {
        this.service = service;
    }

    public Application() {
    }

    public void print() {
        System.out.println(service.findAll().get(0).getFirstName());
    }

    public static void main(String[] args) {

        //ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        //CustomerService service = context.getBean("customerService", CustomerService.class);
        //System.out.println(service.findAll().get(0).getFirstName());
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        Application application = new Application();
        application.print();
    }

}

这是我的应用程序上下文

<?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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd">

    <context:annotation-config></context:annotation-config>
    <context:component-scan base-package="com.pluralsight"></context:component-scan>
</beans>

我的客户服务类(class)

package com.pluralsight.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.pluralsight.model.Customer;
import com.pluralsight.repository.CustomerRepository;

@Service("customerService")
public class CustomerServiceImpl implements CustomerService {

    //@Autowired
    private CustomerRepository customerRepository;

    @Autowired
    public CustomerServiceImpl(CustomerRepository customerRepository) {
        System.out.println("we are using constructor injection");
        this.customerRepository = customerRepository;
    }

    //@Autowired
    public void setCustomerRepository(CustomerRepository customerRepository) {
        System.out.println("we are using setter injection");
        this.customerRepository = customerRepository;
    }

    /* (non-Javadoc)
     * @see com.pluralsight.service.CustomerService#findAll()
     */
    public List<Customer> findAll() {
        return customerRepository.findAll();
    }

}

Answer 1

你需要移动

@Autowired
private CustomerService service;

在应用程序类之外。

要使 Autowiring 工作，所有“连线”类必须由 Spring 容器实例化，但 Application 类已经在容器之前实例化，因此您无法将容器管理的依赖项连接到其中。