1 FactoryBean接口的使用

合集 - Spring5 源码(13)

1.1 FactoryBean接口的使用2024-03-05

2.4 Spring5 自定义标签案例2024-02-213.7 spring 识别自定义实现BeanFactoryPostProcessor 的接口2024-02-214.8 springboot源码解析(四)：监听器2024-03-055.11 replace-method标签使用2024-03-136.10 lookup-method标签使用2024-03-137.通过FactoryMethod创建对象示例2024-03-188.通过Supplier创建对象示例2024-04-149.InstantiationAwareBeanPostProcessor 接口实现2024-03-1810.对象Constructor构造函数和@PostConstruct&@PreDestroy解析详解2024-03-2211.自定义转换器Converter实现案例2024-03-2212.三级缓存解析过程2024-03-2513.JDK proxy 和cglib 源码解读2024-04-08

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一般情况下，Spring通过反射机制利用bean的class属性指定实现类来实例化bean。在某些情况下，实例化bean过程比较复杂，如果按照传统的方式，则需要在标签中提供大量的配置信息，配置方式的灵活性是受限的。为此，spring可以通过实现FactoryBean的接口来定制实例化bean的逻辑。

1 创建User对象#

package com.gientech.factoryBean;



public class User {

    private String id;

    private String userName;

    private String email;

    private String password;

    public User(String userName) {
        this.userName = userName;
    }

    public String getId() {
        return id;
    }

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

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

2 创建MyFactoryBean#

package com.gientech.factoryBean;


import org.springframework.beans.factory.FactoryBean;

public class MyFactoryBean implements FactoryBean<User> {
    @Override
    public User getObject() throws Exception {
        return new User("wangmazi");
    }

    @Override
    public Class<?> getObjectType() {
        return User.class;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }
}

3 修改xml配置文件#

<bean id="userFactory" class="com.gientech.factoryBean.MyFactoryBean">
    <property name="userInfo" value="1,zhangsan,123456@163.com,123qaz"></property>
</bean>

4 测试code和截图#

• 4.1 场景一：获取实现了BeanFactory接口类的对象#

ApplicationContext ac = new ClassPathXmlApplicationContext("factoryBean.xml");
// 获取实现了BeanFactory接口类的对象
MyFactoryBean factoryBean = (MyFactoryBean) ac.getBean("&userFactory");
System.out.println(factoryBean);

此时factoryBean 由Spring管理，且存储于一级缓存中，如下图所示。

• 4.2 场景二：factoryBean#getObject的返回对象存储于factoryBeanObjectCache缓存中#

测试code

ApplicationContext ac = new ClassPathXmlApplicationContext("factoryBean.xml");
// 获取实现了BeanFactory接口类的对象
MyFactoryBean factoryBean = (MyFactoryBean) ac.getBean("&userFactory");
System.out.println(factoryBean);

User bean2 = (User) ac.getBean("userFactory");
System.out.println(bean2.getUserName()+ " ---- " + bean2.getEmail());

bean2是通过getObjectForBeanInstance(sharedInstance, name, beanName, null); 方法创建，此时，factoryBean 由Spring管理，且存储于一级缓存中，bean2存储于factoryBeanObjectCache 缓存中。如下图所示：

• 4.3 场景三：factoryBean#getObject的返回对象为单例时，只有一个对象存储于factoryBeanObjectCache缓存中#

当User.isSingleton() 返回true时， bean2 会存入factoryBeanObjectCache缓存中，bean3 会从缓存中获取，代码和截图所示。

ApplicationContext ac = new ClassPathXmlApplicationContext("factoryBean.xml");
// 获取实现了BeanFactory接口类的对象
MyFactoryBean factoryBean = (MyFactoryBean) ac.getBean("&userFactory");
System.out.println(factoryBean);

User bean2 = (User) ac.getBean("userFactory");
System.out.println(bean2.getUserName()+ " ---- " + bean2.getEmail());

User bean3 = (User) ac.getBean("userFactory");
System.out.println(bean3.getUserName()+ " ---- " + bean3.getEmail());

• 4.3 场景四：factoryBean#getObject的返回对象不为单例时，不由Spring管理，也不存储于factoryBeanObjectCache缓存中#

当User.isSingleton() 返回false时，不是单例对象，bean2,bean3 不会存入factoryBeanObjectCache缓存中，bean2，bean3 都会重新创建，代码和运行截图所示。

package com.gientech.factoryBean;


import org.springframework.beans.factory.FactoryBean;

public class MyFactoryBean implements FactoryBean<User> {

    private String userInfo;

    public String getUserInfo() {
        return userInfo;
    }

    public void setUserInfo(String userInfo) {
        this.userInfo = userInfo;
    }

    @Override
    public User getObject() throws Exception {
        User user = new User();
        String[] arr = userInfo.split(",");
        user.setId(arr[0]);
        user.setUserName(arr[1]);
        user.setEmail(arr[2]);
        user.setPassword(arr[3]);
        return user;
    }

    @Override
    public Class<?> getObjectType() {
        return User.class;
    }

    // 此处返回为false
    @Override
    public boolean isSingleton() {
        return false;
    }
}

ApplicationContext ac = new ClassPathXmlApplicationContext("factoryBean.xml");
        // 获取实现了BeanFactory接口类的对象
        MyFactoryBean factoryBean = (MyFactoryBean) ac.getBean("&userFactory");
        System.out.println(factoryBean);

        User bean2 = (User) ac.getBean("userFactory");
        System.out.println(bean2);

        User bean3 = (User) ac.getBean("userFactory");
        System.out.println(bean3);

factoryBeanObjectCache 截图如下图所示：

运行结果如下图所示