Java Spring 获取Bean的三种方式 Java Spring 获取Bean的三种方式

Java Spring beans的profile属性切换环境 Java Spring beans的profile属性切换环境<beans>标签，除了经常用的作为根标签外，还可以嵌套在根标签内，使用profile属性切换开发环境可以使用以下两种方式指定被激活的环境（dev为环境名）：使用命令行动态参数，虚拟机参数位置加载 -Dspring.profiles.active=dev使用代码的方式设置环境变量System.setProperty("spring.profiles.active","dev")beans.xml <bean class="org.example.UserDaoImpl" id="userDao"/> <bean class="org.example.UserServiceImpl" id="userService"/> <beans profile="dev"> <bean id="userService1" class="org.example.UserServiceImpl"/> </beans> <beans profile="test"> <bean id="userDao1" class="org.example.UserDaoImpl"/> </beans>主函数调用 public static void main(String[] args) { // 指定环境 System.setProperty("spring.profiles.active","dev"); ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); System.out.println(((UserService) applicationContext.getBean("userService"))); System.out.println(((UserDao) applicationContext.getBean("userDao"))); System.out.println(((UserService) applicationContext.getBean("userService1"))); System.out.println(((UserDao) applicationContext.getBean("userDao1"))); }执行结果org.example.UserServiceImpl@589b3632 org.example.UserDaoImpl@45f45fa1 org.example.UserServiceImpl@4c6e276e Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'userDao1' available

Java Spring 命名空间 Java Spring 命名空间Spring的默认标签用到的是Spring的默认命名空间beans.xml<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> </beans>该命名空间约束下的默认标签如下：创建命名空间创建名为context的命名空间beans.xml<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd " > <context:property-placeholder/> </beans>import引入其他配置文件<import>标签，用于导入其他配置文件，项目变大后，就会导致一个配置文件内容过多，可以将一个配置文件根据业务某块进行拆分，拆分后，最终通过<import>标签导入到一个主配置文件中，项目加载主配置文件就连同<import>导入的文件一并加载了<import resource="classpath:beans.xml"></import>alias指定Bean别名断点调试中，BeanFactory下aliasMap中保存了alias指定的别名，并不会影响bean中name标签指定的值，但是也能通过alias指定的别名进行获取bean<bean class="org.example.UserDaoImpl" id="userDao"/> <bean class="org.example.UserServiceImpl" id="userService"/> <alias name="userDao" alias="dao"></alias> <alias name="userService" alias="service"></alias>

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

Java 基于xml的Spring应用 Java 基于xml的Spring应用1.SpringBean 的配置解析Spring开发中主要是对Bean的配置，Bean的常用配置一览如下： 1.Bean的基础配置配置UserDaoImpl由Spring容器负责管理<bean id="userDao" class="org.example.UserDaoImpl"></bean>此时存储到Spring容器（singleObjects单例池）中的Bean的beanName是userDao，值是UserDaoImpl对象，可以根据beanName获取Bean实例applicationContext.getBean("userDao")如果不配置id，则Spring会把当前Bean实例的全限定名作为beanNamepublic static void main(String[] args) { ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); UserDao bean = (UserDao) applicationContext.getBean("org.example.UserDaoImpl"); System.out.println(bean); }如果配置了id，便不能在使用Bean实例的全限定名进行获取，例如：applicationContext.getBean("org.example.UserDaoImpl");配置别名，配置别名后可以使用别名获得Bean对象实例<bean id="userDao" name="aaa,bbb" class="org.example.UserDaoImpl"></bean>2.SpringBean的配置详解1.Bean的范围配置默认情况下，单纯的Spring环境Bean的作用范围有两个：Singleton和Prototypesingleton：单例，默认值，Spring容器创建的时候，就会进行Bean的实例化，并且存储到容器内部的单例池中，每次getBean时都是从单例池中获取相同的Bean实例<bean id="userDao" class="org.example.UserDaoImpl" scope="singleton"></bean>prototype：原型，Spring容器初始化时不会创建Bean实例，只有调用getBean时才会实例化Bean，每次getBean都会创建一个新的Bean实例<bean id="userDao" class="org.example.UserDaoImpl" scope="prototype"></bean>如果是spring-webmvc的情况下，还会增加两个作用范围：request和sessionmaven导包<dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>5.3.7</version> </dependency>request：将创建的对象放在request域当做<bean id="userDao" class="org.example.UserDaoImpl" scope="request"></bean>session：将创建的对象放在session域当做<bean id="userDao" class="org.example.UserDaoImpl" scope="session"></bean>2.Bean的延迟加载当lazy-init设置为true时为延迟加载，也就是当Spring容器创建的时候，不会立即创建Bean实例，等待用到时在创建Bean实例并且存储到单例池中去，后续在使用该Bean直接冲单例池获取，本质上该Bean还是单例的，只对scope设置为singleton的Bean起作用，对prototype无效，对BeanFactory作为容器也无效<bean id="userDao" class="org.example.UserDaoImpl" lazy-init="true"></bean>3.Bean的初始化方法和销毁方法init-method：初始化时运行方法destroy-method：销毁时运行方法，单例模式容器必须显示关闭才会执行这个方法，否则不会执行关闭，又因为ApplicationContext的接口没有关闭容器的方法，所以类型需要使用ClassPathXmlApplicationContext，才有close显式关闭容器，如果不使用显式关闭，则有可能不会执行销毁方法，例如容器挂掉后就无法执行销毁方法beans.xml:<bean id="userDao" class="org.example.UserDaoImpl" init-method="init" destroy-method="destroy"></bean>UserDaoImpl.javapublic class UserDaoImpl implements UserDao{ public void init(){ System.out.println("初始化方法"); } public void destroy(){ System.out.println("销毁方法"); } }主函数调用 public static void main(String[] args) { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); UserDao userDao = (UserDao) applicationContext.getBean("userDao"); System.out.println(userDao); applicationContext.close(); }结果输出初始化方法 org.example.UserDaoImpl@7d68ef40 销毁方法扩展：除此之外，我们还可以通过实现InitializingBean接口，完成一些Bean的初始化操作，比init-method方法优先级要高UserDaoImpl.javapublic class UserDaoImpl implements UserDao, InitializingBean { public void init(){ System.out.println("初始化方法"); } public void destroy(){ System.out.println("销毁方法"); } @Override public void afterPropertiesSet() throws Exception { System.out.println("属性执行之后进行调用"); } }主函数调用public static void main(String[] args) { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); UserDao userDao = (UserDao) applicationContext.getBean("userDao"); System.out.println(userDao); applicationContext.close(); }结果输出属性执行之后进行调用 初始化方法 org.example.UserDaoImpl@5b0abc94 销毁方法4.Bean的实例化配置Spring的实例化方式主要如下两种：构造方式实例化：底层通过构造方法对Bean进行实例化工厂方式实例化：底层通过调用自定义的工厂方法对Bean进行实例化构造方式实例化Bean分为有参构造和无参构造方法实例化，Spring中配置的<bean>几乎都是无参构造，有参构造例子如下：UserDaoImpl.javapublic class UserDaoImpl implements UserDao { public UserDaoImpl(String name){ System.out.println(name); } }有参构造在实例化Bean时，需要参数的注入，通过constructor-arg标签，嵌入在bean标签内部提供构造参数beans.xml<bean id="userDao" class="org.example.UserDaoImpl"> <constructor-arg value="你好"/> </bean>工厂方式实例化Bean，又分为如下三种：静态工厂方法实例化Bean实例工厂方法实例化Bean实现FactoryBean规范延迟实例化Bean静态工厂实例化Bean：创建一个静态方法public class MyBeanFactory1 { public static UserDao userDao(){ return new UserDaoImpl(); } }配置beans.xml文件，factory-method指定静态方法，如果有传参也需要constructor-arg进行传值<bean id="userDao1" class="factory.MyBeanFactory1" factory-method="userDao"></bean>主函数调用public static void main(String[] args) { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); Object useDao1 = applicationContext.getBean("userDao1"); System.out.println(useDao1); }执行结果org.example.UserDaoImpl@159f197实例工厂方法化Bean：创建一个方法public class MyBeanFactory2 { public UserDao userDao(){ return new UserDaoImpl(); } }beans.xml中配置该静态方法对bean，并且再次配置一个bean指向该bean，并且使用方法，如果有传参也需要constructor-arg进行传值<!-- 配置工厂对象 --> <bean id="myBeanFactory2" class="factory.MyBeanFactory2"></bean> <bean id="userDao2" factory-bean="myBeanFactory2" factory-method="userDao"></bean>主函数执行 public static void main(String[] args) { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); Object userDao2 = applicationContext.getBean("userDao2"); System.out.println(userDao2); }结果输出org.example.UserDaoImpl@51e5fc98实现FactoryBean规范延迟实例化Bean类的接口继承于FactoryBean，在BeanFactory创建时便已经创建实例，但是实例的值并不是真实的对象本身，而是当getBean进行调用的时候，才会将实例对象新建调用getObject方法并且存放到缓存池，然后从缓存池取值从而返回实例对象，如果后续进行重复取值，不会再创建一个新的对象，而是从缓存池取值后直接返回，从而实现FactoryBean规范延迟加载Beanpublic class MyBeanFactory3 implements FactoryBean<UserDao> { @Override public UserDao getObject() throws Exception { return new UserDaoImpl(); } @Override public Class<?> getObjectType() { return null; } }主函数调用public static void main(String[] args) { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); Object userDao3 = applicationContext.getBean("userDao3"); Object userDao4 = applicationContext.getBean("userDao3"); System.out.println(userDao3); System.out.println(userDao4); }运行结果org.example.UserDaoImpl@48fa0f47 org.example.UserDaoImpl@48fa0f475.Bean的注入方式 其中，ref是reference的缩写，翻译为参考涉及到意思，用于引入其他Bean的id。value用于注入普通的属性值。6.Bean的依赖注入配置配置注入普通类型的List对象配置接口public interface UserService { public List<String> getStringList(); }配置实现类public class UserServiceImpl implements UserService { //注入List private List<String> stringList; public void setStringList(List<String> stringList) { this.stringList = stringList; } public List<String> getStringList() { return stringList; } }配置Beans.xml文件<bean id="userService" class="org.example.UserServiceImpl"> <property name="stringList"> <list> <value>aaaa</value> <value>bbbb</value> <value>cccc</value> <value>dddd</value> </list> </property> </bean>主函数运行ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml"); UserService userService = (UserService) applicationContext.getBean("userService"); System.out.println(userService.getStringList());运行结果[aaaa, bbbb, cccc, dddd]配置注入引用类型的List对象UserServicelmpl.javapublic List<String> getStringList() { return stringList; } public void setUserDaoList(List<UserDao> userDaoList) { this.userDaoList = userDaoList; }beans.xml需要配置ref或者单独创建bean<bean id="useService1" class="org.example.UserServiceImpl"> <property name="userDaoList"> <list> <bean class="org.example.UserDaoImpl"/> <bean class="org.example.UserDaoImpl"/> <bean class="org.example.UserDaoImpl"/> <bean class="org.example.UserDaoImpl"/> </list> </property> </bean>或者<bean id="userDao1" class="org.example.UserDaoImpl"/> <bean id="userDao2" class="org.example.UserDaoImpl"/> <bean id="userDao3" class="org.example.UserDaoImpl"/> <bean id="userDao4" class="org.example.UserDaoImpl"/> <bean id="useService1" class="org.example.UserServiceImpl"> <property name="userDaoList"> <list> <ref bean="userDao1"/> <ref bean="userDao2"/> <ref bean="userDao3"/> <ref bean="userDao4"/> </list> </property> </bean>配置注入引用类型的set对象配置和List一样，在beans.xml文件中，将list标签改为set配置注入引用类型的map对象配置和List一样，在beans.xml文件中，将list标签改为map，map中标签为entry，key为键名，value为键值，value-ref为引用对象<property name="map"> <map> <entry key="a" value="1111"/> <entry key="b" value="2222"/> </map> </property> <property name="map"> <map> <entry key="a" value-ref="userDao1"/> <entry key="b" value-ref="userDao2"/> </map> </property>