Spring中bean标签scope的基本实现

1、创建一个Bean对象，相当于Spring中的标签，用于定义id和classPath

package javaNote.aopSingleton;

public class BeanDefined {
    private String id;
    private String classPath;
    //默认为singleton
    private String scope = "singleton";

    public String getScope() {
        return scope;
    }

    public void setScope(String scope) {
        this.scope = scope;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getClassPath() {
        return classPath;
    }

    public void setClassPath(String classPath) {
        this.classPath = classPath;
    }
}

2、实体类

package javaNote.aopSingleton;

public class Student {
    private String sName;
    private int age;

    public Student() {
        this.age = 19;
        this.sName = "Mike";
    }

    public String getsName() {
        return sName;
    }

    public void setsName(String sName) {
        this.sName = sName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "sName='" + sName + '\'' +
                ", age=" + age +
                '}';
    }
}

3、工厂模式，BeanFactory来获取实例，利用HashMap来保存实例

package javaNote.aopSingleton;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

public class BeanFactory {
    //存放bean的集合
    private List<BeanDefined> beanDefinedList;
    //存放已经创建好的实例
    private Map<String, Object> springIoc;

    public BeanFactory(List<BeanDefined> beanDefinedList) throws Exception {
        this.beanDefinedList = beanDefinedList;
        springIoc = new HashMap<>();
        for (BeanDefined bean : beanDefinedList){
            //如果参数是singleton，那么就创建实例
            if (Objects.equals(bean.getScope(), "singleton")){
                Class<?> classFile = Class.forName(bean.getClassPath());
                Object instance = classFile.getDeclaredConstructor().newInstance();
                //以singleton为键值保存在hashMap中
                springIoc.put(bean.getScope(), instance);
            }
        }
    }

    public Object getBean(String beanId) throws Exception {
        Object instance = null;
        //获取beaId
        for (BeanDefined bean : beanDefinedList){
            //判断bean的id是否相同
            if (beanId.equals(bean.getId())){
                //判断是否prototype，原型模式，如果是，那么就创建实例
                if (Objects.equals(bean.getId(), "prototype")){
                    String classPath = bean.getClassPath();
                    Class<?> classFile = Class.forName(classPath);
                    instance = classFile.getDeclaredConstructor().newInstance();
                    return instance;
                }
                //如果不是，那么就从springIoc中取出来
                return springIoc.get("singleton");
            }
        }
        return null;
    }
}

4、测试类

package javaNote.aopSingleton;

import java.util.ArrayList;
import java.util.List;

public class BeanTest {
    public static void main(String[] args) throws Exception {
        //1、声明注册
        BeanDefined defined = new BeanDefined();
        defined.setId("student");
        defined.setClassPath("javaNote.aopSingleton.Student");
        List<BeanDefined> beanList = new ArrayList<>();
        beanList.add(defined);
        //2、声明一个BeanFactory，类似于Spring中的ApplicationContext
        //被标记的类
        BeanFactory factory = new BeanFactory(beanList);
        //开发人员向BeanFactory索要实例
        Student student1 = (Student)factory.getBean("student");
        System.out.println(student1.hashCode());
        Student student2 = (Student)factory.getBean("student");
        System.out.println(student2.hashCode());
        //打印出来的结果，说明 scope 属性的singleton，标志的类会存储在Spring框架中
        // 214126413
        //214126413
    }
}