文章目录

• • 1. 项目搭建过程
  • • 1. pom 依赖
    • 2. 在没有配置数据库相关时不要引入依赖包，如spring-boot-starter-data-jpa
  • 2. spring bean 默认生成策略的正确使用
  • • 1. 代码示例
    • 2. 单元测试
    • 3. 工具类 [参考](#test2)
    • 4. 报错信息
    • 5. 分析
    • 6. 使用说明
  • 2. 使用了@Autowired 注解，任然是空指针
  • • 1. 不理解Spring的自动装配规则，错误的是用new是很常见的
    • 2. 没有理解spring 的扫描机制
  • 3. 不使用自动注入还会获取上下文么？
  • • 1. 应用上下文的理解
    • 2. Spring 核心是容器，但容器不是唯一
    • • 1. 不常用的容器实现 -- BeanFactory
      • 2. 高级实现，继承BeanFactory派生的应用上下文 -- ApplicationContext
      • 3. 获取应用上下文（ApplicationContext）的四种方式
      • • 1. ApplicationContextInitializer: 容器创建之后的回调
        • 2. ApplicationListener : 观察者模式的典型应用
        • 3. 获取应用上下文 ApplicationContextAware ： Spring 的Aware接口
  • 4. 多线程下Spring Bean 的数据不符合预期怎么办
  • • 1. 单例
    • 2. coding
    • 3. spring 单利Bean 的 特点
    • • 1. 优点
      • 2. 劣势
      • 3. 默认单例的理由
  • 5. 经常报存在多个可用Bean 异常
  • • 1. 与Spring bean 相关的注解
    • • 1. @Autowired
      • 2. @Qualifiler
      • 3. @Resource
      • 4. @Primary

1. 项目搭建过程

1. pom 依赖

learningcom.maidou1.0-SNAPSHOT4.0.0spring-escapespring-escapehttp://www.example.comUTF-81.71.7org.springframework.bootspring-boot-dependencies2.6.4pomimportjunitjunit4.13.1testorg.springframework.bootspring-boot-starter-web2.6.4org.projectlomboklombok1.18.24org.springframework.bootspring-boot-starter-test2.6.4mysqlmysql-connector-java8.0.21runtimeorg.apache.commonscommons-lang33.8.1maven-clean-plugin3.1.0maven-resources-plugin3.0.2maven-compiler-plugin3.8.0maven-surefire-plugin2.22.1maven-jar-plugin3.0.2maven-install-plugin2.5.2maven-deploy-plugin2.8.2maven-site-plugin3.7.1maven-project-info-reports-plugin3.0.0

2. 在没有配置数据库相关时不要引入依赖包，如spring-boot-starter-data-jpa

2. spring bean 默认生成策略的正确使用

1. 代码示例

package com.maidou.spring.escape.service;import org.springframework.stereotype.Service;@Service
public class ORderService {public void getOrder() {System.out.println("this is order");}
}

2. 单元测试

package com.maidou.spring.escape.service;import com.maidou.spring.escape.utils.ApplicationUtils;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;import static org.junit.Assert.*;@SpringBootTest
@RunWith(SpringRunner.class)
public class ORderServiceTest {@Testpublic void getOrder() {ORderService oRderService = (ORderService)ApplicationUtils.getBean("oRderService");oRderService.getOrder();}
}

3. 工具类 参考

package com.maidou.spring.escape.utils;import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;/*** 
应用上下文工具类
* */
@Slf4j
@Component
public class ApplicationUtils implements ApplicationContextAware {private static ApplicationContext applicationContext = null;@Overridepublic void setApplicationContext(ApplicationContext applicationContext)throws BeansException {if (ApplicationUtils.applicationContext == null) {ApplicationUtils.applicationContext = applicationContext;}}public static ApplicationContext getApplicationContext() {return ApplicationUtils.applicationContext;}/*** 
通过 name 获取 Bean
* */public static Object getBean(String name) {return getApplicationContext().getBean(name);}/*** 
通过 class 获取 Bean
* */public static  T getBean(Class clazz) {return getApplicationContext().getBean(clazz);}/*** 
通过 name + class 获取 Bean
* */public static  T getBean(String name, Class clazz) {return getApplicationContext().getBean(name, clazz);}
}

4. 报错信息

org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'oRderService' availableat org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:874)at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1344)at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:309)at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)

5. 分析

AnnotationBeanNameGenerator -> generateBeanName  -> Introspector.decapitalize(shortClassName)

    public static String decapitalize(String name) {if (name == null || name.length() == 0) {return name;}// 第一个字母和第二个字母都是大写的话本名输出if (name.length() > 1 && Character.isUpperCase(name.charAt(1)) &&Character.isUpperCase(name.charAt(0))){return name;}char chars[] = name.toCharArray();chars[0] = Character.toLowerCase(chars[0]);return new String(chars);}

6. 使用说明

1. 避免首字母和第二个字母都是大写，否则全名输出 ORderService
2. 注解的时候主动指定名称 @Service(“oRderService”)
3. 通过类型的方式获取对象信息

2. 使用了@Autowired 注解，任然是空指针

1. 不理解Spring的自动装配规则，错误的是用new是很常见的

1. 属性对象注入了，但是，当前类没有被标记为new

2. 当前类标记为spring bean,且属性对象也注入了，但是，确实用了new去过去了对象

解决方式 : 使用bean 的整个过程中，都应该被Spring容器所管理

2. 没有理解spring 的扫描机制

1. 创建外部类

   import org.springframework.stereotype.Service;@Service
   public class Outer {public void test() {System.out.println("outer test");}
   }
   

2. 单元测试

     @Testpublic void testOuter() {assert ApplicationUtils.getApplicationContext().containsBean("outer");((Outer)ApplicationUtils.getBean("outer")).test();}
   

3. 错误

   java.lang.AssertionErrorat com.maidou.spring.escape.service.ORderServiceTest.testOuter(ORderServiceTest.java:26)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:498)at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)

4. 解决方式 启动类增加扫描包信息

   @ComponentScan(value = {"com.maidou.spring.escape","com.maidou.spring.outer"})
   

5. @ComponentScan 参数说明

   1. vaule
   2. includeFilters
   3. excludeFilters
   4. lazyInit

3. 不使用自动注入还会获取上下文么？

1. 应用上下文的理解

Spring的核心是管理对象，且并不只是帮我们创建对象，他负责了对象整个生命的管理，创建、装配、销毁

他是IOC容器

应用上下文可以认为是Spring容器的一种实现，也就是用于操作容器类对象

把需要管理的对象放入容器中，取得容器中的Bean

2. Spring 核心是容器，但容器不是唯一

1. 不常用的容器实现 – BeanFactory

  1. 最简单的容器2. 提供基本的DI功能

2. 高级实现，继承BeanFactory派生的应用上下文 – ApplicationContext

  1. 解析配置文件2. 注册管理Bean

3. 获取应用上下文（ApplicationContext）的四种方式

1. ApplicationContextInitializer: 容器创建之后的回调

   定义在org.springframwork.context包下，两步实现

package com.maidou.spring.escape.application_context;import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;/*** 
保存应用上下文
* */
@Slf4j
public class ApplicationContextStore  {private static ApplicationContext applicationContext = null;public static void setApplicationContext(ApplicationContext applicationContext) {log.info("coming in applicationContextStore");if (ApplicationContextStore.applicationContext == null) {ApplicationContextStore.applicationContext = applicationContext;}}public static ApplicationContext getApplicationContext() {return ApplicationContextStore.applicationContext;}
}

获取应用上下文

package com.maidou.spring.escape.application_context;import lombok.extern.slf4j.Slf4j;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;/*** @Author maicheng* @Description : 第一种方式获取应用上下文* @Date 13:13 2022/10/22**/
@Slf4j
public class UserInitializer implements ApplicationContextInitializer {@Overridepublic void initialize(ConfigurableApplicationContext applicationContext) {assert ApplicationContextStore.getApplicationContext() == null;ApplicationContextStore.setApplicationContext(applicationContext);assert ApplicationContextStore.getApplicationContext() != null;log.info("get UserInitializer");}
}

注册到启动类上

   public static void main(String[] args) {
//        SpringApplication.run(App.class, args);SpringApplication  application = new SpringApplication(App.class);application.addInitializers(new UserInitializer());application.run(args);}

2. ApplicationListener : 观察者模式的典型应用

1. 观察者的典型应用(内置事件)

   ApplicationContexntEvent

   1. ContextRefreshedEvent
   2. ContextStartedEvent
   3. ContextStoppedEvent
   4. ContextClosedEvent

2. coding

   package com.maidou.spring.escape.application_context;import lombok.extern.slf4j.Slf4j;
   import org.springframework.context.ApplicationListener;
   import org.springframework.context.event.ContextRefreshedEvent;
   import org.springframework.stereotype.Component;/*** @Author maicheng* @Description* @Date 13:28 2022/10/22**/
   @Slf4j
   @Component
   public class UserListener implements ApplicationListener {@Overridepublic void onApplicationEvent(ContextRefreshedEvent event) {assert ApplicationContextStore.getApplicationContext() == null;ApplicationContextStore.setApplicationContext(event.getApplicationContext());assert ApplicationContextStore.getApplicationContext() != null;log.info("get UserListener");}
   }
   

3. 注释掉 注册的UserInitializer

3. 获取应用上下文 ApplicationContextAware ： Spring 的Aware接口

1. BeanNameAware
2. BeanFactoryAware
3. ApplicationContextAware
4. ResourseLoaderAware

coding

package com.maidou.spring.escape.application_context;import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;/*** @Author maicheng* @Description ：第三种应用上下文的方式* @Date 13:44 2022/10/22**/
@Component
@Slf4j
public class UserAware implements ApplicationContextAware {@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {assert ApplicationContextStore.getApplicationContext() == null;ApplicationContextStore.setApplicationContext(applicationContext);assert ApplicationContextStore.getApplicationContext() != null;log.info("get UserAware");}
}

启动类原始启动 参考

4. 多线程下Spring Bean 的数据不符合预期怎么办

1. 单例

2. coding

package com.maidou.spring.escape.singleton_;import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;import javax.annotation.PostConstruct;
import java.util.ArrayList;
import java.util.List;@Slf4j
@Service
public class DefaultSingleton {private List list = null;@PostConstructpublic void init() {log.info("Coming  in DefaultSingleton");this.list = new ArrayList<>(100);}public void add(String result) {list.add(result);}public int getSize() {return list.size();}public List getList() {return this.list;}
}

测试

package com.maidou.spring.escape.singleton_;import com.maidou.spring.escape.utils.ApplicationUtils;
import lombok.extern.slf4j.Slf4j;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;import static org.junit.Assert.*;@SpringBootTest
@RunWith(SpringRunner.class)
@Slf4j
public class DefaultSingletonTest {@Testpublic void init() {DefaultSingleton bean = ApplicationUtils.getBean(DefaultSingleton.class);DefaultSingleton bean1 = ApplicationUtils.getBean(DefaultSingleton.class);assert bean.hashCode() == bean1.hashCode();bean.add("11111");bean.add("222222");log.info("bean info : {}", bean.getList());bean1.add("33333");log.info("bean info : {}", bean.getList());}
}

映射成多个对象 改变scope 模式

@Scope(BeanDefinition.SCOPE_PROTOTYPE)

3. spring 单利Bean 的 特点

1. 优点

1. 减少新生成实例的消耗
2. 减少JVM垃圾回收
3. 可以快速获取到Bean

2. 劣势

线程不安全

3. 默认单例的理由

1. 少创建实例
2. 垃圾回收便捷
3. 使用缓存快速获取

5. 经常报存在多个可用Bean 异常

1. 与Spring bean 相关的注解

1. @Autowired

属于Spring 框架，默认使用类型(byType)进行注入

2. @Qualifiler

结合@Autowired一起使用，自动注入策略由byType变成byName

3. @Resource

JAVAEE 自带的注解，默认按byName自动注入

4. @Primary

存在多个类型的相同类型的Bean,则 @Primary用于定义首选项