spring ioc 创建对象和DI 依赖注入

港控/mmm° 2022-10-05 06:58 203阅读 0赞

一篇非常好的帮助理解的文章：[https://www.cnblogs.com/xdp-gacl/p/4249939.html][https_www.cnblogs.com_xdp-gacl_p_4249939.html]

# 工厂类非静态方法创建对象： #

在application.xml中先注入工厂类bean，然后利用方法名注入工厂类方法返回的bean

`objectFactory1：工厂类的bean对象名`

`com.sunj.entity.ObjectFactory ：工厂类`

`factory-bean="objectFactory1" 用到的工厂类`

`factory-method="getUser2" 使用工厂类的哪个方法`

`id="user4" 工厂类方法返回的实体对象`

# 工厂类静态方法创建对象 #

<bean id="getUser" class="com.sunj.entity.ObjectFactory" factory-method="getUser"></bean>

# set方法注入对象 #

package com.sunj.dao;
    
    public class UserDao {
        public void add(){
            System.out.println("添加方法");
        }
    }

package com.sunj.service;
    
    import com.sunj.dao.UserDao;
    
    public class UserService {
        private UserDao userDao;
    
        public void add(){
            System.out.println("service方法");
            userDao.add();
        }
    
        public void setUserDao(UserDao userDao) {
            this.userDao = userDao;
        }
    }

这里说明下，需要依赖某对象或者属性时一定要写set方法，spring 容器在读取配置时会通过反射执行它的set方法，如果没有set方法会报错

可以理解下，如果没有这个某方法，但是你一定会在执行它时报错。

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService' defined in class path resource [applicationContext.xml]: Error setting property values; nested exception is org.springframework.beans.NotWritablePropertyException: Invalid property 'userDao' of bean class [com.sunj.service.UserService]: Bean property 'userDao' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1361)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1086)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:293)
    	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:290)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:192)
    	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
    	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:895)
    	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:425)
    	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    	at com.sunj.entity.Test2.main(Test2.java:10)
    Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property 'userDao' of bean class [com.sunj.service.UserService]: Bean property 'userDao' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
    	at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:1052)
    	at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:921)
    	at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:76)
    	at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:58)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1358)
    	... 13 more

[https_www.cnblogs.com_xdp-gacl_p_4249939.html]: https://www.cnblogs.com/xdp-gacl/p/4249939.html