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代码通过getBean();方式从容器中获取指定的Bean实例,容器首先会调用Bean类的无参构造器,创建空值的实例对象。
举例:
首先我在applicationContext.xml配置文件中配置了一个bean:
<?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=" "><!-- 注册Service 这里相当于容器做了SomeServiceImpl myService = new SomeServiceImpl(); --><bean id="myService" class="com.ietree.spring.basic.ioc.SomeServiceImpl"/></beans>
创建SomeServiceImpl对象,但需要注意的是该类的只具有带参构造函器,没有无参构造器:
package com.ietree.spring.basic.ioc;/** * 实现类 * * @author Root */public class SomeServiceImpl implements ISomeService {private int a; // 这里注释掉了无参构造函数,希望容器通过带参构造函数创建对象// public SomeServiceImpl() {// System.out.println("执行无参构造器,创建SomeServiceImpl对象");// }public SomeServiceImpl(int a) {this.a = a; } @Overridepublic void doSomeThing() { System.out.println("执行doSomeThing()方法..."); } }
测试:
@Testpublic void testConstructor() {// 创建容器对象,加载Spring配置文件// ClassPathXmlApplicationContext会从类路径下查找配置文件ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml"); ISomeService service = (ISomeService) ac.getBean("myService"); service.doSomeThing(); }
此时程序会报以下的错误:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'myService' defined in class path resource [applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.ietree.spring.basic.ioc.SomeServiceImpl]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.ietree.spring.basic.ioc.SomeServiceImpl.<init>() at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1155) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1099) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83) at com.ietree.spring.basic.test.MyTest.testConstrutor(MyTest.java:67) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.ietree.spring.basic.ioc.SomeServiceImpl]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.ietree.spring.basic.ioc.SomeServiceImpl.<init>()at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:85) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1147) ... 36 more Caused by: java.lang.NoSuchMethodException: com.ietree.spring.basic.ioc.SomeServiceImpl.<init>() at java.lang.Class.getConstructor0(Unknown Source) at java.lang.Class.getDeclaredConstructor(Unknown Source) at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:80) ... 37 more
解析:这里的错误报的很明显,没有发现默认的构造器。
修改:为该类加上无参构造器:
package com.ietree.spring.basic.ioc;/** * 实现类 * * @author Root */public class SomeServiceImpl implements ISomeService {private int a; public SomeServiceImpl() { System.out.println("执行无参构造器,创建SomeServiceImpl对象"); }public SomeServiceImpl(int a) {this.a = a; } @Overridepublic void doSomeThing() { System.out.println("执行doSomeThing()方法..."); } }
此时,再次运行测试用例,会发现运行成功。
结论:Spring容器实际上是使用了类的反射机制,会首先调用Bean类的无参构造器创建实例对象。
创建SomeServiceImpl类:
package com.ietree.spring.basic.ioc;/** * 实现类 * * @author Root */public class SomeServiceImpl implements ISomeService {public SomeServiceImpl() { System.out.println("执行无参构造器,创建SomeServiceImpl对象"); } @Overridepublic void doSomeThing() { System.out.println("执行doSomeThing()方法..."); } }
创建工厂类ServiceFactory:
package com.ietree.spring.basic.ioc;/** * 工厂类 * * @author Root */public class ServiceFactory {public ISomeService getSomeService() {return new SomeServiceImpl(); } }
使用动态工厂方式获取Bean对象,配置如下:
<?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=" "><!-- 注册动态工厂 --><bean id="factory" class="com.ietree.spring.basic.ioc.ServiceFactory"/><!-- 注册Service:动态工厂Bean --><bean id="myService" factory-bean="factory" factory-method="getSomeService"/></beans>
在这里并没有注册SomeServiceImpl类,而是通过ServiceFactory工厂的getSomeService方法获取的。
测试:
@Testpublic void testFactory1() { ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml"); ISomeService service = (ISomeService) ac.getBean("myService"); service.doSomeThing(); }
运行成功。
静态工厂和动态工厂不同的是,静态工厂中使用的是静态方法创建对象,如:
package com.ietree.spring.basic.ioc;/** * 工厂类 * * @author Root */public class ServiceFactory { // 使用静态方法创建对象public static ISomeService getSomeService() {return new SomeServiceImpl(); } }
对应的配置文件修改如下:
<?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=" "><!-- 注册Service:静态工厂Bean --><bean id="myService" class="com.ietree.spring.basic.ioc.ServiceFactory" factory-method="getSomeService"/></beans>
测试:
@Testpublic void testFactory1() { ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml"); ISomeService service = (ISomeService) ac.getBean("myService"); service.doSomeThing(); }
成功创建SomeServiceImpl对象。
Bean的作用域(scope)分为四种,分别是singleton、prototype、request、session。
scope:
singleton(默认):单例模式,其对象的创建时机是在Spring容器初始化时创建,是默认值
prototype:原型模式,其对象的创建时机不是在Spring容器初始化时创建,而是在代码中真正访问时才创建,每次使用getBean方法获取的同一个
request:对于每次HTTP请求,都将会产生一个不同的Bean实例
session:对于每个不同的HTTP session,都将会产生一个不同的Bean实例
验证:
首先配置作用域为singleton:
<bean id="myService" class="com.ietree.spring.basic.ioc.SomeServiceImpl" scope="singleton"/>
测试:
@Testpublic void test05() { ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml"); ISomeService service1 = (ISomeService) ac.getBean("myService"); ISomeService service2 = (ISomeService) ac.getBean("myService"); System.out.println("service1 = service2吗?" + (service1 == service2)); }
程序输出:
调用无参构造器 service1 = service2吗?true
结论:当作用域为singleton单例模式时,只会创建一个对象实例,并且对象是在Spring容器初始化时创建。
同样,当配置为prototype原型模式时:
<bean id="myService" class="com.ietree.spring.basic.ioc.SomeServiceImpl" scope="prototype"/>
程序输出:
调用无参构造器 调用无参构造器 service1 = service2吗?false
结论:构造器被调用了两次,说明创建的service1和service2不是同一个对象,并且对象是在被使用到时才创建的。
Bean后处理器是一种特殊的Bean,容器中所有的Bean在初始化时,均会自动执行该类的两个方法。由于该Bean是由其它Bean自动调用执行,不是程序员手工调用,故此Bean无须id属性。
需要做的是,在Bean后处理器类方法中,只要对Bean类与Bean类中的方法进行判断,就可实现对指定的Bean的指定的方法进行功能扩展与增强。方法返回的Bean对象,即是增强过的对象。
代码中需要自定义Bean后处理器类,该类就是实现了接口BeanPostProcessor的类。该接口中包含两个方法,分别在目标Bean初始化完毕之前与之后执行,它的返回值为功能被扩展或增强后的Bean对象。
举例:利用Bean后处理器实现大小写字符串转换
接口类ISomeService:
/** * 接口类 * * @author Root */public interface ISomeService { String doSomeThing(); }
实现类SomeServiceImpl:
/** * 实现类 * * @author Root */public class SomeServiceImpl implements ISomeService {public SomeServiceImpl() { System.out.println("调用无参构造器"); } // 返回小写字母“abcde” @Overridepublic String doSomeThing() {return "abcde"; } }
定义Bean处理器MyBeanPostProcessor:
import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;/** * Bean后处理器 * * @author Root */public class MyBeanPostProcessor implements BeanPostProcessor {// bean:表示当前正在进行初始化的Bean对象// beanName:表示当前正在进行初始化的Bean对象的id @Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { System.out.println("执行----before()方法---");return bean; } @Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println("执行----after()方法---"); Object obj = Proxy.newProxyInstance( bean.getClass().getClassLoader(), bean.getClass().getInterfaces(),new InvocationHandler() { @Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable { Object invoke = method.invoke(bean, args);return ((String) invoke).toUpperCase(); } });return obj; } }
使用JDK动态代理实现大小写转换的功能。
配置文件:
<bean id="myService" class="com.ietree.spring.basic.ioc.method2.SomeServiceImpl"/><!-- 注册Bean后处理器,由于该Bean是由其它Bean自动调用执行,不是程序员手工调用,故此Bean无须id属性 --><bean class="com.ietree.spring.basic.ioc.method2.MyBeanPostProcessor"></bean>
注意:Bean后处理器不需要配置id的,因为它是随着对象的创建自动调用的。
测试:
@Testpublic void test05() { ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml"); ISomeService service = (ISomeService) ac.getBean("myService"); String result = service.doSomeThing(); System.out.println(result); }
程序输出:
调用无参构造器 执行----before()方法---执行----after()方法---ABCDE
增强成功。可以判断代理类的类型,进行对单个或单独一类对象做增强。
Bean实例从创建到最后销毁,需要经过很多过程,执行很多生命周期方法。
Step1:调用无参构造器,创建实例对象。
Step2:调用参数的setter,为属性注入值。
Step3:若Bean实现了BeanNameAware接口,则会执行接口方法setBeanName(String beanId),使Bean类可以获取其在容器中的id名称。
Step4:若Bean实现了BeanFactoryAware接口,则执行接口方法setBeanFactory(BeanFactory factory),使Bean类可以获取到BeanFactory对象。
Step5:若定义并注册了Bean后处理器BeanPostProcessor,则执行接口方法postProcessBeforeInitialization()。
Step6:若Bean实现了InitializingBean接口,则执行接口方法afterPropertiesSet()方法。该方法在Bean的所有属性的set方法执行完毕后执行,是Bean初始化结束的标志,即Bean实例化结束。
Step7:若设置了init-method方法,则执行。
Step8:若定义并注册了Bean后处理器BeanPostProcessor,则执行接口方法postProcessAfterInitialization().
Step9:执行业务方法。
Step10:若Bean实现了DisposableBean接口,则执行接口方法destroy()。
Step11:若设置了destroy-method方法,则执行。
举例:
创建接口类ISomeService:
/** * 接口类 * * @author Root */public interface ISomeService { void doSomeThing(); }
创建接口实现类SomeServiceImpl:
import org.springframework.beans.BeansException;import org.springframework.beans.factory.BeanFactory;import org.springframework.beans.factory.BeanFactoryAware;import org.springframework.beans.factory.BeanNameAware;import org.springframework.beans.factory.DisposableBean;import org.springframework.beans.factory.InitializingBean;/** * 实现类 * * @author Root */public class SomeServiceImpl implements ISomeService, BeanNameAware, BeanFactoryAware, InitializingBean, DisposableBean { // 两个属性private String adao;private String bdao; public void setAdao(String adao) {this.adao = adao; System.out.println("Step2:执行settter"); }public void setBdao(String bdao) {this.bdao = bdao; System.out.println("Step2:执行settter"); }public SomeServiceImpl() { System.out.println("Step1:调用无参构造器"); } @Overridepublic void doSomeThing() { System.out.println("Step9:执行doSomeThing()"); } public void setUp(){ System.out.println("Step7:初始化完毕之后 "); } public void tearDown(){ System.out.println("Step11:销毁之前"); } @Overridepublic void setBeanName(String name) { System.out.println("Step3:获取到bean的id = " + name); } @Overridepublic void setBeanFactory(BeanFactory beanFactory) throws BeansException { System.out.println("Step4:获取到BeanFactory容器 "); } @Overridepublic void afterPropertiesSet() throws Exception { System.out.println("Step6:Bean初始化完毕了 "); } @Overridepublic void destroy() throws Exception { System.out.println("Step10:实现的接口销毁之前 "); } }
创建BeanPostProcessor接口的实现类MyBeanPostProcessor:
import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;/** * Bean后处理器 * * @author Root */public class MyBeanPostProcessor implements BeanPostProcessor {// bean:表示当前正在进行初始化的Bean对象// beanName:表示当前正在进行初始化的Bean对象的id @Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { System.out.println("Step5:执行----before()方法---");return bean; } @Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println("Step8:执行----after()方法---");return bean; } }
配置applicationContext.xml文件:
<?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=" "><!-- 注册Service --><bean id="myService" class="com.ietree.spring.basic.ioc.method3.SomeServiceImpl" init-method="setUp" destroy-method="tearDown"><property name="adao" value="aaa"></property><property name="bdao" value="bbb"></property></bean><!-- 注册Bean后处理器,由于该Bean是由其它Bean自动调用执行,不是程序员手工调用,故此Bean无须id属性 --><bean class="com.ietree.spring.basic.ioc.method3.MyBeanPostProcessor"></bean></beans>
测试类:
@Testpublic void test05() { String resource = "com/ietree/spring/basic/ioc/method3/applicationContext.xml"; ApplicationContext ac = new ClassPathXmlApplicationContext(resource); ISomeService service = (ISomeService) ac.getBean("myService"); service.doSomeThing();// 对于销毁方法的执行,有两个条件:// 1)当前的Bean需要是singleton的// 2)要手工关闭容器 ((ClassPathXmlApplicationContext) ac).close(); }
程序输出:
Step1:调用无参构造器 Step2:执行settter Step2:执行settter Step3:获取到bean的id = myService Step4:获取到BeanFactory容器 Step5:执行----before()方法---Step6:Bean初始化完毕了 Step7:初始化完毕之后 Step8:执行----after()方法---Step9:执行doSomeThing() Step10:实现的接口销毁之前 Step11:销毁之前
正如程序输出的序列一样,此顺序即是对象创建的调用顺序,在编程中可以在某一个过程对其进行增强操作。
一般情况下,命名
id的命名需要满足XML对ID属性命名规范:必须以字母开头,可以包含字母、数字、下划线、连字符、句号、冒号。
name属性值可以包含各种字符。
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