2025年【springboot】3.1ioc容器简介

大家好，我是讯享网，很高兴认识大家。

inversion of control
初学Java可能使用new创建对象。但spring通过描述来创建对象。
spring boot不建议使用xml，而是通过注解描述生成对象。

spring中每一个需要管理的对象称为bean，spring管理这些bean的容器，称为ioc容器。
ioc容器需要具备2个基本功能：
1.通过描述发布和获取bean
2.通过描述完成bean直接的依赖关系

在spring中，所有的ioc容器都要实现顶级容器接口BeanFactory
接口中有多个getBean方法，意味着允许我们按照类型或者名称获取bean
isSingleton判断bean是否为单例
ioc容器中默认bean都为单例，即getBean返回同一个对象

简单体验一下applicationContext
在这里插入图片描述
讯享网

package com.springboot.chapter3.pojo; / * @author KNOE * @date 2020-09-21 12:15 */ public class User { 
    private Long id; private String userName; private String note; // alt+insert public Long getId() { 
    return id; } public void setId(Long id) { 
    this.id = id; } public String getUserName() { 
    return userName; } public void setUserName(String userName) { 
    this.userName = userName; } public String getNote() { 
    return note; } public void setNote(String note) { 
    this.note = note; } }

讯享网

讯享网package com.springboot.chapter3.config; import com.springboot.chapter3.pojo.User; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; / * @author KNOE * @date 2020-09-21 12:20 */ @Configuration public class AppConfig { 
    @Bean(name = "user") public User initUser() { 
    User user = new User(); user.setId(1L); user.setUserName("user_name_1"); user.setNote("note_1"); return user; } }

@Configuration表示这个一个配置文件，spring会根据他来生成ioc容器装配bean
@Bean表示讲该方法返回的pojo装配到ioc容器中。其属性name定义bean的名称，
如果不写，方法名就是bean的名称

package com.springboot.chapter3.config; import com.springboot.chapter3.pojo.User; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; import org.springframework.context.annotation.AnnotationConfigApplicationContext; / * @author KNOE * @date 2020-09-21 12:23 */ public class IoCTest { 
    private static Logger log = LogManager.getLogger(IoCTest.class); public static void main(String[] args) { 
    AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class); User user = ctx.getBean(User.class); log.info(user.getId()); } }

将配置文件appConfig传递给一个构造方法。于是可以用getBean方法获取pojo

讯享网import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; private static Logger logger = LogManager.getLogger(myClass.class);

在这里插入图片描述
可以看到bean的属性能够输出出来

通过component装配bean

把user改成这样

package com.springboot.chapter3.pojo; import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Component; / * @author KNOE * @date 2020-09-21 12:15 */ @Component("user") public class User { 
    @Value("1") private Long id; @Value("user_name_1") private String userName; @Value("note_1") private String note; // alt+insert public Long getId() { 
    return id; } public void setId(Long id) { 
    this.id = id; } public String getUserName() { 
    return userName; } public void setUserName(String userName) { 
    this.userName = userName; } public String getNote() { 
    return note; } public void setNote(String note) { 
    this.note = note; } }

component表面要被ioc容器扫描装配。如果不配置name
会自动把类名小写作为bean名称
@Value指定具体的值，注入对应属性

改造appConfig

讯享网package com.springboot.chapter3.config; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; / * @author KNOE * @date 2020-09-21 12:20 */ @Configuration @ComponentScan("com.springboot.chapter3.*") public class AppConfig { 
    }

@ComponentScan会让类扫描，这样就能删掉创建对象方法
但是默认只能扫描本包和子包
需要特别定义扫描的包

@ComponentScan(value = "com.springboot.chapter3.*", excludeFilters = { 
   @ComponentScan.Filter(classes = { 
   myClass.class})})

还可以这样写，排除不想注入的类

自定义第三方bean

但是这不代表bean没用了。经常需要引入第三方的包，希望把其中的类也放到ioc容器中。这时@Bean注解就有用了。因为componentScan顶多扫描项目里的类，第三方的类都不在项目文件里，也没法扫描，也加不了@Component tree

讯享网package com.springboot.chapter3.pojo; import org.springframework.stereotype.Service; / * @author KNOE * @date 2020-09-21 16:11 */ @Service public class UserService { 
    public void print(User user) { 
    System.out.println("user = " + user.getId()); } }

新写一个service类

<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.3.4.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>springboot</groupId> <artifactId>chapter3</artifactId> <version>0.0.1-SNAPSHOT</version> <name>chapter3</name> <description>Chapter3 project for Spring Boot</description> <properties> <java.version>11</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-dbcp2</artifactId> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project>

在xml里加入sql的依赖

讯享网package com.springboot.chapter3.config; import org.apache.commons.dbcp2.BasicDataSourceFactory; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; import org.springframework.stereotype.Service; import javax.sql.DataSource; import java.util.Properties; / * @author KNOE * @date 2020-09-21 12:20 */ @Configuration @ComponentScan(value = "com.springboot.chapter3.*", excludeFilters = { 
   @ComponentScan.Filter(classes = { 
   Service.class})}) public class AppConfig { 
    @Bean(name = "dataSource") public DataSource getDataSource() { 
    Properties props = new Properties(); props.setProperty("driver", "com.driver.jdbc.Driver"); props.setProperty("url", "jdbc:mysql://localhost:3306/testdb"); props.setProperty("username", "root"); props.setProperty("password", ""); DataSource dataSource = null; try{ 
    dataSource = BasicDataSourceFactory.createDataSource(props); }catch (Exception e) { 
    e.printStackTrace(); } return dataSource; } }

测试一下

package com.springboot.chapter3.config; import com.springboot.chapter3.pojo.User; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import javax.sql.DataSource; / * @author KNOE * @date 2020-09-21 12:23 */ public class IoCTest { 
    private static Logger log = LogManager.getLogger(IoCTest.class); public static void main(String[] args) { 
    AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class); User user = ctx.getBean(User.class); log.info(user.getId()); DataSource dataSource = ctx.getBean(DataSource.class); log.info(dataSource.getClass()); } }

没有任何问题
在这里插入图片描述

2025年【springboot】3.1ioc容器简介

通过component装配bean

自定义第三方bean

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