Spring5核心原理-FactoryBean详解

使用 FactoryBean 创建 bean

public class EmployeeFactoryBean extends AbstractFactoryBean<Object>
{
    /This method will be called by container to create new instances
    @Override
    protected Object createInstance() throws Exception
    {
        //code
    }

    //This method is required for autowiring to work correctly
    @Override
    public Class<EmployeeDTO> getObjectType() {
        return EmployeeDTO.class;
    }
}

为什么要使用FactoryBean？

1. 从 JNDI 中查找对象（例如数据源）时，可以使用JndiObjectFactoryBean.
2. 当使用经典 Spring AOP 为 bean 创建代理时，您可以使用ProxyFactoryBean.
3. 在 IoC 容器中创建 Hibernate 会话工厂时，可以使用LocalSessionFactoryBean.

FactoryBean 演示

public class EmployeeDTO {

	private Integer id;
	private String firstName;
	private String lastName;
	private String designation;

	//Setters and Getters are hidden behind this comment.

	@Override
	public String toString() {
		return "Employee [id=" + id + ", firstName=" + firstName
				+ ", lastName=" + lastName + ", type=" + designation + "]";
	}
}

import com.howtodoinjava.demo.model.EmployeeDTO;

public class EmployeeFactoryBean extends AbstractFactoryBean<Object> 
{
	private String designation;
	
	public String getDesignation() {
		return designation;
	}

	public void setDesignation(String designation) {
		this.designation = designation;
	}

	//This method will be called by container to create new instances
	@Override
	protected Object createInstance() throws Exception 
	{
		EmployeeDTO employee = new EmployeeDTO();
		employee.setId(-1);
		employee.setFirstName("dummy");
		employee.setLastName("dummy");
		//Set designation here
		employee.setDesignation(designation);
		return employee;
	}

	//This method is required for autowiring to work correctly
	@Override
	public Class<EmployeeDTO> getObjectType() {
		return EmployeeDTO.class;
	}
}

<bean id="manager"  class="com.howtodoinjava.demo.factory.EmployeeFactoryBean">
	<property name="designation" value="Manager" />
</bean>

<bean id="director"  class="com.howtodoinjava.demo.factory.EmployeeFactoryBean">
	<property name="designation" value="Director" />
</bean>

public class TestSpringContext 
{
  @SuppressWarnings("resource")
  public static void main(String[] args) 
  {
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
 
    EmployeeDTO manager = (EmployeeDTO) context.getBean("manager");
    System.out.println(manager);
     
    EmployeeDTO director = (EmployeeDTO) context.getBean("director");
    System.out.println(director);
  }
}
 

Employee [id=-1, firstName=dummy, lastName=dummy, type=Manager]
Employee [id=-1, firstName=dummy, lastName=dummy, type=Director]

获取 FactoryBean 实例本身

EmployeeFactoryBean factory = (EmployeeFactoryBean) context.getBean("&director");
 
System.out.println(factory.getDesignation());
System.out.println(factory.getObjectType());
System.out.println(factory.getObject());
 

Director
 
class com.leftso.demo.model.EmployeeDTO
 
Employee [id=-1, firstName=dummy, lastName=dummy, type=Director]

标签2： spring核心原理 FactoryBean详解 spring boot

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