Spring study notes: Realize the IOC and DI of the spring framework based on two configuration methods of XML files and annotations

First open IntelliJ IDEA, create a Maven project spring-lesson, delete the src folder, and only keep the pom file corresponding to maven dependencies. This project is used as the parent project, and the <packaging> node is added to the pom file. The content of the node is pom, indicating the construction Aggregate engineering, as follows:

 <groupId>com.winning</groupId>
  <artifactId>spring-lesson</artifactId>
  <version>1.0-SNAPSHOT</version>
  <!--表示构建聚合工程-->
  <packaging>pom</packaging>

Add a new module to the parent project. The module name is day1-spring. First, introduce spring-related dependencies, which are mainly spring-context dependencies, as follows:

<dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.2.5.RELEASE</version>
</dependency>

Then add a package: com.winning.dao, add an interface TestDAO, which has a hello() method:

package com.winning.dao;

public interface TestDAO {
    void hello();
}

package com.winning.dao;

import org.springframework.stereotype.Repository;

@Repository
public class TestDAOImpl implements TestDAO {
    @Override
    public void hello() {
        System.out.println("-->dao层TestDAOImpl执行hello()方法!");
    }
}

Continue to add packages, com.winning.service, and create a TestService interface, which has a CallDaoMethod method:

package com.winning.service;

import com.winning.dao.TestDAO;

public interface TestService {

    void CallDaoMethod();
    void  setTestDAO(TestDAO testDAO);
}

@Service
public class TestServiceImpl implements TestService {

    @Autowired // 把spring容器中TestDAO类型实例注入到testDAO属性中
    TestDAO testDao;

    @Override
    public void CallDaoMethod() {

        System.out.println("-->service层TestServiceImpl执行CallDaoMethod()方法!");
        testDao.hello();
    }

    @Override
    public void setTestDAO(TestDAO testDAO) {
        this.testDao = testDAO;
    }

}

In the service layer code above, there is a property of type TestDAO. To ensure that this property can be injected, a set method must be provided for the property.

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Next, let's implement the management of java bean objects through the xml configuration file, and add an applicationContext.xml file under the resources folder

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       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.xsd">

    <bean id="testDao" class="com.winning.dao.TestDAOImpl" />
    <bean id="testService" class="com.winning.service.TestServiceImpl">
        <!--配置属性的依赖注入，前提是属性有set方法-->
        <property name="TestDAO" ref="testDao" />
    </bean>
</beans>

It should be noted here that the id must be unique, and the class node represents the class path, that is, the package name + class name. At the same time, when the DAO layer object is injected into the service layer, we use attribute injection, and the ref node corresponds to the attribute name.

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Next, let's test, load our xml configuration file through the ClassPathXmlApplicationContext class, the parameter name is the xml file name, as follows:

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

Below we use this method to obtain the DAO layer and service layer objects respectively

//通过xml文件管理java bean对象
        ApplicationContext context =
                new ClassPathXmlApplicationContext("applicationContext.xml");

        Object testDaoObj = context.getBean("testDao");
        System.out.println( testDaoObj );

        //TestService.class，表示返回指定Bean类型,无需用Object接收
        TestService testService = context.getBean("testService", TestService.class);
        testService.CallDaoMethod();

Run it to see the result:

It has been successful, and the space is limited. Let’s share the annotation implementation method next time.