手写SpringIOC容器如何实现

IOC_自定义对象容器

创建实体类

package com.neu.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
* @Author yqq
* @Date 2022/05/12 18:23
* @Version 1.0
*/
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
private int id;
private String name;
private Integer age;
}

创建Dao接口和实现类

接口

public interface StudentDao {
Student findById(int id);
}

实现类

public class StudentDaoImpl implements StudentDao {
@Override
public Student findById(int id) {
return new Student(1,"yqq",23);
}
}

创建配置文件bean.properties

studentDao=com.neu.dao.StudentDaoImpl
studentService=com.neu.service.StudentService

创建容器类

该类在类加载时读取配置文件，将配置文件中
配置的对象全部创建并放入容器中。

/**
* @Author yqq
* @Date 2022/05/12 18:31
* @Version 1.0
* 容器类，负责管理对象，在类加载时读取配置文件并创建对象
*/
public class Container {

static Map<String,Object> map = new HashMap<>();
static {
//读取配置文件
InputStream is = Container.class.getClassLoader().getResourceAsStream("bean.properties");
Properties properties = new Properties();
try{
properties.load(is);
}catch (Exception e){
e.printStackTrace();
}
//遍历配置文件中的所有对象
Enumeration<Object> keys = properties.keys();
while (keys.hasMoreElements()){
String key = keys.nextElement().toString();
String value = properties.getProperty(key);
try {
//反射原理创建对象
Object o = Class.forName(value).newInstance();
map.put(key,o);
} catch (Exception e) {
e.printStackTrace();
}
}
}
//从容器中获得对象
public static Object getBean(String key){
return map.get(key);
}
}

创建Dao对象的调用者StudentService

public class StudentService {
public Student findStudentById(int id){
//从容器中获取对象
StudentDao studentDao = (StudentDao)Container.getBean("studentDao");
//StudentDao studentDao = new StudentDaoImpl();
return studentDao.findById(1);
}
}

测试StudentService

public class Test {
public static void main(String[] args) {
StudentService service = (StudentService)Container.getBean("studentService");
System.out.println(service.findStudentById(1));
}
}

• StudentService从容器中每次拿到的都是同一个
  StudentDao对象，节约了资源。