基于注解和配置类的方式实现IOC注入

工程结构

常规三层架构实现

dao 层

package com.example.dao;

import com.example.pojo.Student;

import java.util.List;

public interface StudentDao {
    public List<Student> queryAll();
}

package com.example.dao.impl;

import com.example.pojo.Student;
import com.example.dao.StudentDao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.BeanPropertyRowMapper;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository // ioc 容器注入的必须是一个 实现类，不能是接口，因此 ioc注解 必须标注在实现类上面
public class StudentDaoImpl implements StudentDao {

    // jdbcTemplate 也从 ioc 容器中获取，在配置类中配置该bean，在整体都加入ioc容器中，他们一起都是透明可见的
    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Override
    public List<Student> queryAll() {
        String sql = "select id, name, gender, age, class as classes from students;";
        List<Student> studentList = jdbcTemplate.query(sql, new BeanPropertyRowMapper<>(Student.class));
        return studentList;
    }
}

service 层

package com.example.service;

import com.example.pojo.Student;

import java.util.List;

public interface StudentService {
    public List<Student> findAll();
}

package com.example.service.impl;

import com.example.pojo.Student;
import com.example.dao.StudentDao;
import com.example.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentDao studentDao;

    @Override
    public List<Student> findAll() {
        List<Student> studentList = studentDao.queryAll();
        return studentList;
    }
}

controller 层

package com.example.controller;

import com.example.pojo.Student;
import com.example.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;

import java.util.List;

// 注入ioc
@Controller
public class StudentController {

    @Autowired
    private StudentService studentService;

    public void getList() {
        List<Student> studentList = studentService.findAll();
        System.out.println(studentList);
    }
}

配置类

package com.example.config;

import com.alibaba.druid.pool.DruidDataSource;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.jdbc.core.JdbcTemplate;

import javax.sql.DataSource;

// 配置类，首先使用配置类注解
@Configuration
// 开启包扫描注解，value 是一个 String[]，那么 String[] 的实例化是怎么写的呢？String[] strs = new String(){};
@ComponentScan(value = {"com.example"})
// 加载外部资源注解
@PropertySource(value = {"classpath:jdbc.properties"})
public class JavaConfig {

    // DruidDataSource bean 组件声明在ioc容器中
    @Bean
    public DataSource createDataSource(@Value("${atguigu.url}") String url, @Value("${atguigu.driver}") String driver,
                                       @Value("${atguigu.username}") String username, @Value("${atguigu.password}") String password) {
        DruidDataSource druidDataSource = new DruidDataSource();
        druidDataSource.setUrl(url);
        druidDataSource.setDriverClassName(driver);
        druidDataSource.setUsername(username);
        druidDataSource.setPassword(password);
        return druidDataSource;
    }

    // 注入 ioc 中，同时需要引用到 createDataSource
    @Bean
    public JdbcTemplate createJdbcTemplate(DataSource createDataSource) {
        JdbcTemplate jdbcTemplate = new JdbcTemplate();
        jdbcTemplate.setDataSource(createDataSource);
        return jdbcTemplate;
    }
}

测试

package com.example;

import com.example.config.JavaConfig;
import com.example.controller.StudentController;
import org.junit.jupiter.api.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class TestIoC {

    /**
     * 注解+配置类实现 ioc 容器注入的方式的测试
     */
    @Test
    public void test() {
        // 1. 构造 ioc 容器
        ApplicationContext applicationContext
            = new AnnotationConfigApplicationContext(JavaConfig.class);
        // 2. 获取 bean
        StudentController controller = applicationContext.getBean(StudentController.class);
        controller.getList();
    }
}