Java Spring 自动装配 Java Spring 自动装配如果被注入的属性类型是Bean引用的话，那么可以在<bean>标签中使用autowire属性去配置自动注入方式，属性值有两个byName：通过属性名自动装配，即去匹配setXxx与id="xxx"(name="xxx")是否一致；byType：通过Bean的类型从容器中匹配，匹配出多个相同Bean类型，报错。beans.xml<bean class="org.example.UserDaoImpl" id="userDao"/> <bean class="org.example.UserServiceImpl" id="userService" autowire="byName"/> <bean class="org.example.UserServiceImpl" id="userService1" autowire="byType"/>UserServicepublic interface UserService { public void show(); }UserServiceImplpublic class UserServiceImpl implements UserService { private UserDao userDao; public void setUserDao(UserDao userDao){ this.userDao = userDao; } @Override public void show() { System.out.println(userDao); } }主函数调用public static void main(String[] args) { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); ((UserService) applicationContext.getBean("userService")).show(); ((UserService) applicationContext.getBean("userService1")).show(); }执行结果org.example.UserDaoImpl@1f0f1111 org.example.UserDaoImpl@1f0f1111如果xml文件自动装配中有多个同类型的bean容器将会报错例如：<bean class="org.example.UserDaoImpl" id="userDao"/> <bean class="org.example.UserDaoImpl" id="userDao1"/> <bean class="org.example.UserServiceImpl" id="userService" autowire="byName"/> <bean class="org.example.UserServiceImpl" id="userService1" autowire="byType"/>IDEA报错提示无法自动装配。存在多个 'UserDao' 类型的 Bean。Bean: userDao1,userDao。属性: 'userDao'运行结果提示警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService1' defined in class path resource [beans.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'org.example.UserDao' available: expected single matching bean but found 2: userDao,userDao1 Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService1' defined in class path resource [beans.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'org.example.UserDao' available: expected single matching bean but found 2: userDao,userDao1