首页 > 代码库 > Spring框架第一篇之Bean的装配
Spring框架第一篇之Bean的装配
一、默认装配方式
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=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 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; } @Override public void doSomeThing() { System.out.println("执行doSomeThing()方法..."); } }
测试:
@Test public 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; } @Override public 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。
二、动态工厂Bean
三、静态工厂Bean
四、容器中的Bean的作用域
五、Bean后处理器
六、定制Bean的生命周期
七、<bean/>标签的id属性与name属性
Spring框架第一篇之Bean的装配
声明:以上内容来自用户投稿及互联网公开渠道收集整理发布,本网站不拥有所有权,未作人工编辑处理,也不承担相关法律责任,若内容有误或涉及侵权可进行投诉: 投诉/举报 工作人员会在5个工作日内联系你,一经查实,本站将立刻删除涉嫌侵权内容。