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Spring @Component、@Service、@Repository 和 @Controll

@Autowired注解，但是我们已经使用xml配置来配置bean并将其注入到容器中，但是如果您使用@Component、@Service、@Repository和@Controller注解并启用组件自动扫描，spring会自动将这些bean导入到容器中容器，您不必在 xml 文件中明确定义它们。 所以基本上所有 4 个注解都用于将 bean 定义注册到 Spring 的应用程序上下文中。

@Component ：

@Component 是bean 定义的通用注解，并在应用程序上下文中注册。

@Service

@Service 是专门的组件注解，用于注解属于服务层的类。

@Repository

@Repository 注解是专门的组件注解，用于在 DAO 层对类进行注解。它还使未经检查的异常有资格转换为 Spring DataAccessException。

@Controller

@Controller 注解是专门的组件注解，用于在表示层对类进行注解。它广泛用于 Spring MVC 应用程序中。

除非您确定它不属于@Service、@Repository 和@Controller 注释，否则不应使用@Component 注释。

启用组件扫描：

只有当您在 applicationcontext.xml 中使用context:component-scan时，所有这些注释才会起作用。它基本上扫描以上 4 个带注释的类，并使用 Spring 应用程序上下文注册 bean。

<context:component-scan base-package="org.arpit.java2blog" />

Spring注解示例：

在这个例子中，我们将使用上面的注解在控制器、服务和 Dao 类的帮助下创建国家对象。 让我们首先创建我们的 bean 类 Country.java

package org.arpit.java2blog.bean;

public class Country{

String countryName;
long population;

public Country() {
  super();
}
public Country(String countryName,long population) {
  super();
  this.countryName = countryName;
  this.population=population;
}

public String getCountryName() {
  return countryName;
}
public void setCountryName(String countryName) {
  this.countryName = countryName;
}
public long getPopulation() {
  return population;
}
public void setPopulation(long population) {
  this.population = population;
}

}

CountryController,java

package org.arpit.java2blog.controller;

import org.arpit.java2blog.bean.Country;
import org.arpit.java2blog.service.CountryService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;

@Controller ("countryController")
public class CountryController
{
     @Autowired
    CountryService countryService;

    public Country createNewCountry()
    {
        return countryService.createNewCountry();
    }
}

CountryService.java

package org.arpit.java2blog.service;

import org.arpit.java2blog.bean.Country;
import org.arpit.java2blog.dao.CountryDAO;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service("countryService")
public class CountryService {
    @Autowired
CountryDAO countryDAO;
public Country createNewCountry() {

  return countryDAO.createNewCountry();
}

}

CountryDAO.java

package org.arpit.java2blog.dao;

import org.arpit.java2blog.bean.Country;
import org.springframework.stereotype.Repository;

@Repository("countryDAO")
public class CountryDAO {

public Country createNewCountry() {
  // You should get it from database
  Country country = new Country("Ïndia", 40000);
  return country;
}

}

applicationcontext.xml

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd">
<context:component-scan base-package="org.arpit.java2blog" />
</beans>

SpringApplicationMain.java

package org.arpit.java2blog.main;

import org.arpit.java2blog.bean.Country;
import org.arpit.java2blog.controller.CountryController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringApplicationMain {
public static void main(String[] args) {

  ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
  CountryController controller = (CountryController) context.getBean("countryController");
  Country country = controller.createNewCountry();
  System.out.println("Country Name : " + country.getCountryName());
  System.out.println("Country's Population : " + country.getPopulation());
}
}

当你运行上面的程序时，你会得到下面的输出：

Aug 08, 2016 12:00:42 AM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1c2709da: startup date [Mon Aug 08 00:00:42 IST 2016]; root of context hierarchy
Aug 08, 2016 12:00:42 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
Country Name : Ïndia
Country's Population : 40000

原文链接：https://codingdict.com/

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