Spring Boot文档阅读笔记-Spring Boot @Bean解析

谁借莪１个温暖的怀抱￠ 2022-11-15 01:09 211阅读 0赞

利用SpringBoot的@Bean创建一个简单的Bean。

Spring的@Bean注解是放在方法上的，带上这个注解的方法会被Spring容器管理。并且这个方法要返回一个值（对象），这个值和对象会被BeanFactory注册为Bean。

下面是一个例子

程序运行截图如下：

![20210330151632485.png][]

项目结构如下：

pom.xml
    src
    ├───main
    │   ├───java
    │   │   └───cn
    │   │       └───it1995
    │   │               DemoApplication.java
    │   │               AppName.java
    │   └───resources
    │           application.properties
    │           logback.xml
    └───test
        └───java

下面是Maven代码，spring-boot-starer是核心启动包，他包含自动配置、日志、YAML。

<?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>2.4.3</version>
            <relativePath/> 
        </parent>
        <groupId>cn.it1995</groupId>
        <artifactId>demo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <name>demo</name>
        <description>Demo project for Spring Boot</description>
        <properties>
            <java.version>1.8</java.version>
        </properties>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <optional>true</optional>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                    <configuration>
                        <excludes>
                            <exclude>
                                <groupId>org.projectlombok</groupId>
                                <artifactId>lombok</artifactId>
                            </exclude>
                        </excludes>
                    </configuration>
                </plugin>
            </plugins>
        </build>
    
    </project>

下面定义一个简单的接口，用于返回应用名

package cn.it1995.demo;
    
    interface AppName {
    
        String getName();
    }

application.peroperties文件包含了应用配置的设置。spring.main.banner-mode配置了Spring内部的属性，将其关闭，将spring.main.log-startup-info也关掉。新增app.name这个自定义属性

spring.main.banner-mode=off
    spring.main.log-startup-info=false
    app.name=SpringBootBean

下面是logbak.xml文件，用于配置日志的。设置日志等级为ERROR。这个功能是在spring-boot-starter包中的。

<?xml version="1.0" encoding="UTF-8"?>
    <configuration>
        <include resource="org/springframework/boot/logging/logback/base.xml" />
        <logger name="org.springframework" level="ERROR"/>
        <logger name="cn.it1995" level="INFO"/>
    </configuration>

下面是启动类，包含bean的创建

package cn.it1995.demo;
    
    import org.springframework.beans.factory.annotation.Value;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.CommandLineRunner;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.context.annotation.Bean;
    
    @SpringBootApplication
    public class DemoApplication implements CommandLineRunner {
    
        private static final Logger logger = LoggerFactory.getLogger(DemoApplication.class);
    
        public static void main(String[] args) {
    
            SpringApplication.run(DemoApplication.class, args);
        }
    
        @Override
        public void run(String... args) throws Exception {
    
            logger.info("Application name: {}", appName.getName());
        }
    
        @Autowired
        private AppName appName;
    
        @Bean
        public AppName getAppName(@Value("${app.name}") String appName) {
    
            
            return () -> appName;
        }
    }

@SpringBootApplication开启了自动装配和组建扫描；

@Autowired注解获将AppName的Bean注入进去了；

@Bean用于创建一个Bean，让Spring容器进行管理；

@Value获取application.properties中app.name的值。

源码打包下载地址：

[https://github.com/fengfanchen/Java/tree/master/SpringBootBean][https_github.com_fengfanchen_Java_tree_master_SpringBootBean]

[20210330151632485.png]: /images/20221022/86214d6f1dc84ee6bd44748e9844ead3.png
[https_github.com_fengfanchen_Java_tree_master_SpringBootBean]: https://github.com/fengfanchen/Java/tree/master/SpringBootBean