springboot原理实战(4)-springboot入口分析

喜欢ヅ旅行 2023-07-13 03:58 3阅读 0赞

### 文章目录 ###

*  目录
 *  一、环境搭建2种方式
 *   *  ①继承父组件
     *  ②第2种引入方式:
 *  二.@SpringBootApplication注解分析
 *   *  案例1：入口替换为@ComponentScan
     *  案例2：@SpringBootConfiguration替换@Configuration
 *  三、两种启动方式
 *   *  ①默认的静态方法运行
     *  ②new SpringApplication()方式启动

# 目录 #

从现在开始进入springboot项目入门，先来张本文的概要脑图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70]

# 一、环境搭建2种方式 #

这里说的是Pom引入springboot的包的方式:

## ①继承父组件 ##

<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>2.2.5.RELEASE</version>
            <relativePath/> 
        </parent>
        <groupId>com.demo</groupId>
        <artifactId>springboot2-demo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <name>springboot2-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.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>
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                </plugin>
            </plugins>
        </build>
    
    </project>

关键是这里:  
![在这里插入图片描述][20200310142617703.png]

## ②第2种引入方式: ##

不继承spring-boot-starter-parent。  
我们从maven中央仓库找到这个包:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 1]  
修改下：  
这样引入:

<dependency>
       <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-dependencies</artifactId>
        <version>2.2.5.RELEASE</version>
        <scope>import</scope>
        <type>pom</type>
    </dependency>

全部的pom如下:

<?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>
        
        <groupId>com.demo</groupId>
        <artifactId>springboot2-demo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <name>springboot2-demo</name>
        <description>Demo project for Spring Boot</description>
    
        <properties>
            <java.version>1.8</java.version>
        </properties>
            <dependencyManagement>
                <dependencies>
                    <dependency>
                        <groupId>org.springframework.boot</groupId>
                        <artifactId>spring-boot-dependencies</artifactId>
                        <version>2.2.5.RELEASE</version>
                        <scope>import</scope>
                        <type>pom</type>
                    </dependency>
                </dependencies>
            </dependencyManagement>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter</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>
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                </plugin>
            </plugins>
        </build>
    
    </project>

上面的2种方式都可以。

# 二.@SpringBootApplication注解分析 #

我们看下启动类上有个注解@SpringBootApplication注解  
，这个注解，满足我们的所有想象，帮我们做了都很多的工作。  
来段代码:

@SpringBootConfiguration
    public class Springboot2DemoApplication { 
    
        @Bean
        public Runnable createRunnable(){ 
            return () -> { 
                System.out.println("spirng boot is started");
            };
        }
    
        public static void main(String[] args) { 
            ConfigurableApplicationContext context = SpringApplication.run(Springboot2DemoApplication.class, args);
            context.getBean(Runnable.class).run();
            System.out.println(context.getBean(User.class));
        }
    
    }

点击注解看到，它是个组合注解:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 2]

*  @ComponentScan 可以扫描当前包下的组件。
 *  @SpringBootConfiguration把入口类配置成一个Configuration配置类。它包含了  
    @Configuration注解。  
    ![在这里插入图片描述][2020031014340054.png]
 *  @EnableAutoConfiguration自动配置，功能强大，以后说。

## 案例1：入口替换为@ComponentScan ##

定义一个bean

@Component
    public class User { 
    }

修改入口注解:

@ComponentScan
    public class App2 { 
        @Bean
        public Runnable createRunnable(){ 
            return () -> { 
                System.out.println("spirng boot is started");
            };
        }
    
        public static void main(String[] args) { 
            ConfigurableApplicationContext context = SpringApplication.run(App2.class, args);
            context.getBean(Runnable.class).run();
            System.out.println(context.getBean(User.class));
            System.out.println(context.getBean(List.class));
        }
    
    }

运行结果:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 3]  
完美。  
说明什么?

> 说明@ComponentScan扫描到了User对象，容器拿到这个bean。  
> 但是这个入口类为啥能拿到Runnable这个类？我们明明去掉了SpringBootConfiguration，不能把这个类当成配置类了啊。

解答:  
我们看下入口的run的方法：  
![在这里插入图片描述][20200310144238189.png]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 4]  
答案在这里。  
这里会把入口类这个resouce类默认配置到容器中，所以可以当做配置类来使用。

## 案例2：@SpringBootConfiguration替换@Configuration ##

演示@SpringBootConfiguration是否有配置功能：

@SpringBootConfiguration
    public class MyConfig { 
    
        @Bean
        public List createList(){ 
            return new ArrayList();
        }
    }

测试:

@ComponentScan
    public class Springboot2DemoApplication { 
    
        @Bean
        public Runnable createRunnable(){ 
            return () -> { 
                System.out.println("spirng boot is started");
            };
        }
    
        public static void main(String[] args) { 
            ConfigurableApplicationContext context = SpringApplication.run(Springboot2DemoApplication.class, args);
            context.getBean(Runnable.class).run();
            System.out.println(context.getBean(List.class));
        }
    
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 5]  
可以看出已经注入进来了。

# 三、两种启动方式 #

## ①默认的静态方法运行 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 6]

官方默认是这种方式，使用SpringApplication调用run方法，运行整个springboot项目。现在换一种方式启动：

## ②new SpringApplication()方式启动 ##

@ComponentScan
    public class App { 
    @Bean
        public Runnable createRunnable(){ 
            return () -> { 
                System.out.println("spirng boot is started");
            };
        }
        public static void main(String[] args) { 
            SpringApplication app = new SpringApplication(App.class);
    // Set<String> sets = new HashSet<>();
    // sets.add(App.class.getName());
    // app.setSources(sets);
            ConfigurableApplicationContext context = app.run(args);
            context.getBean(Runnable.class).run();
            System.out.println(context.getBean(User.class));
        }
    }

看下效果:  
![在这里插入图片描述][20200310145121744.png]  
也可以这样写：

@ComponentScan
    public class App { 
       @Bean
        public Runnable createRunnable(){ 
            return () -> { 
                System.out.println("spirng boot is started");
            };
        }
        public static void main(String[] args) { 
            SpringApplication app = new SpringApplication();
            Set<String> sets = new HashSet<>();
            sets.add(App.class.getName());
            app.setSources(sets);
            ConfigurableApplicationContext context = app.run(args);
            context.getBean(Runnable.class).run();
            System.out.println(context.getBean(User.class));
        }
    }

结果完美：  
![在这里插入图片描述][20200310145417463.png]  
同时，还可以调用其他的入口：  
比如从新写个类，没有@ComponentScan，当前类也没有注入bean

public class App2 { 
    
        public static void main(String[] args) { 
            SpringApplication app = new SpringApplication();
            Set<String> sets = new HashSet<>();
            sets.add(App.class.getName());
            app.setSources(sets);
            ConfigurableApplicationContext context = app.run(args);
            context.getBean(Runnable.class).run();
            System.out.println(context.getBean(User.class));
            System.out.println(context.getBean(List.class));
        }
    
    }

可以看到这里调用的是其他的入口类  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 7]  
显示结果也ok:

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 8]

--------------------

个人微信公号：  
搜索： 怒放de每一天  
不定时推送相关文章，期待和大家一起成长！！  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 9]

--------------------

完

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200310142258963.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[20200310142617703.png]: https://img-blog.csdnimg.cn/20200310142617703.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200310142731107.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20200310143147903.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[2020031014340054.png]: https://img-blog.csdnimg.cn/2020031014340054.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/20200310143843186.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[20200310144238189.png]: https://img-blog.csdnimg.cn/20200310144238189.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 4]: https://img-blog.csdnimg.cn/20200310144251905.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 5]: https://img-blog.csdnimg.cn/20200310144741441.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 6]: https://img-blog.csdnimg.cn/20200310144909443.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[20200310145121744.png]: https://img-blog.csdnimg.cn/20200310145121744.png
[20200310145417463.png]: https://img-blog.csdnimg.cn/20200310145417463.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 7]: https://img-blog.csdnimg.cn/20200310145714377.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 8]: https://img-blog.csdnimg.cn/20200310145800300.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70 9]: https://img-blog.csdnimg.cn/2020030915352597.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70