• SpringBoot怎么用之原理分析与配置


    1.1 起步依赖原理分析

    1.1.1 分析spring-boot-starter-parent

    按住Ctrl点击pom.xml中的spring-boot-starter-parent,跳转到了spring-boot-starter-parent的pom.xml,xml配置如下(只摘抄了部分重点配置):

    <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-dependencies</artifactId>
      <version>2.0.1.RELEASE</version>
      <relativePath>../../spring-boot-dependencies</relativePath>
    </parent>
    

    按住Ctrl点击pom.xml中的spring-boot-starter-dependencies,跳转到了spring-boot-starter-dependencies的pom.xml,xml配置如下(只摘抄了部分重点配置):

    <properties>
      	<activemq.version>5.15.3</activemq.version>
      	<antlr2.version>2.7.7</antlr2.version>
      	<appengine-sdk.version>1.9.63</appengine-sdk.version>
      	<artemis.version>2.4.0</artemis.version>
      	<aspectj.version>1.8.13</aspectj.version>
      	<assertj.version>3.9.1</assertj.version>
      	<atomikos.version>4.0.6</atomikos.version>
      	<bitronix.version>2.1.4</bitronix.version>
      	<build-helper-maven-plugin.version>3.0.0</build-helper-maven-plugin.version>
      	<byte-buddy.version>1.7.11</byte-buddy.version>
      	... ... ...
    </properties>
    <dependencyManagement>
      	<dependencies>
          	<dependency>
            	<groupId>org.springframework.boot</groupId>
            	<artifactId>spring-boot</artifactId>
            	<version>2.0.1.RELEASE</version>
          	</dependency>
          	<dependency>
            	<groupId>org.springframework.boot</groupId>
            	<artifactId>spring-boot-test</artifactId>
            	<version>2.0.1.RELEASE</version>
          	</dependency>
          	... ... ...
    	</dependencies>
    </dependencyManagement>
    <build>
      	<pluginManagement>
        	<plugins>
          		<plugin>
            		<groupId>org.jetbrains.kotlin</groupId>
            		<artifactId>kotlin-maven-plugin</artifactId>
            		<version>${kotlin.version}</version>
          		</plugin>
          		<plugin>
            		<groupId>org.jooq</groupId>
            		<artifactId>jooq-codegen-maven</artifactId>
            		<version>${jooq.version}</version>
          		</plugin>
          		<plugin>
            		<groupId>org.springframework.boot</groupId>
            		<artifactId>spring-boot-maven-plugin</artifactId>
            		<version>2.0.1.RELEASE</version>
          		</plugin>
              	... ... ...
        	</plugins>
      	</pluginManagement>
    </build>
    

    从上面的spring-boot-starter-dependencies的pom.xml中我们可以发现,一部分坐标的版本、依赖管理、插件管理已经定义好,所以我们的SpringBoot工程继承spring-boot-starter-parent后已经具备版本锁定等配置了。所以起步依赖的作用就是进行依赖的传递。

    1.1.2 分析spring-boot-starter-web

    按住Ctrl点击pom.xml中的spring-boot-starter-web,跳转到了spring-boot-starter-web的pom.xml,xml配置如下(只摘抄了部分重点配置):

    <?xml version="1.0" encoding="UTF-8"?>
    <project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
      	<modelVersion>4.0.0</modelVersion>
      	<parent>
        	<groupId>org.springframework.boot</groupId>
        	<artifactId>spring-boot-starters</artifactId>
        	<version>2.0.1.RELEASE</version>
      	</parent>
      	<groupId>org.springframework.boot</groupId>
      	<artifactId>spring-boot-starter-web</artifactId>
      	<version>2.0.1.RELEASE</version>
      	<name>Spring Boot Web Starter</name>
      
      	<dependencies>
        	<dependency>
          		<groupId>org.springframework.boot</groupId>
          		<artifactId>spring-boot-starter</artifactId>
          		<version>2.0.1.RELEASE</version>
          		<scope>compile</scope>
        	</dependency>
        	<dependency>
          		<groupId>org.springframework.boot</groupId>
          		<artifactId>spring-boot-starter-json</artifactId>
          		<version>2.0.1.RELEASE</version>
          		<scope>compile</scope>
        	</dependency>
        	<dependency>
          		<groupId>org.springframework.boot</groupId>
          		<artifactId>spring-boot-starter-tomcat</artifactId>
          		<version>2.0.1.RELEASE</version>
          		<scope>compile</scope>
        	</dependency>
        	<dependency>
          		<groupId>org.hibernate.validator</groupId>
          		<artifactId>hibernate-validator</artifactId>
          		<version>6.0.9.Final</version>
          		<scope>compile</scope>
        	</dependency>
        	<dependency>
          		<groupId>org.springframework</groupId>
          		<artifactId>spring-web</artifactId>
          		<version>5.0.5.RELEASE</version>
          		<scope>compile</scope>
        	</dependency>
        	<dependency>
          		<groupId>org.springframework</groupId>
          		<artifactId>spring-webmvc</artifactId>
          		<version>5.0.5.RELEASE</version>
          		<scope>compile</scope>
        	</dependency>
      	</dependencies>
    </project>
    
    

    从上面的spring-boot-starter-web的pom.xml中我们可以发现,spring-boot-starter-web就是将web开发要使用的spring-web、spring-webmvc等坐标进行了“打包”,这样我们的工程只要引入spring-boot-starter-web起步依赖的坐标就可以进行web开发了,同样体现了依赖传递的作用。

    1.2 自动配置原理解析

    按住Ctrl点击查看启动类MySpringBootApplication上的注解@SpringBootApplication

    @SpringBootApplication
    public class MySpringBootApplication {
        public static void main(String[] args) {
            SpringApplication.run(MySpringBootApplication.class);
        }
    }
    

    注解@SpringBootApplication的源码

    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @SpringBootConfiguration
    @EnableAutoConfiguration
    @ComponentScan(excludeFilters = {
    		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
    		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
    public @interface SpringBootApplication {
    
    	/**
    	 * Exclude specific auto-configuration classes such that they will never be applied.
    	 * @return the classes to exclude
    	 */
    	@AliasFor(annotation = EnableAutoConfiguration.class)
    	Class<?>[] exclude() default {};
    
    	... ... ...
    
    }
    

    其中,

    @SpringBootConfiguration:等同与@Configuration,既标注该类是Spring的一个配置类

    @EnableAutoConfiguration:SpringBoot自动配置功能开启

    按住Ctrl点击查看注解@EnableAutoConfiguration

    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @AutoConfigurationPackage
    @Import(AutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration {
    	... ... ...
    }
    

    其中,@Import(AutoConfigurationImportSelector.class) 导入了AutoConfigurationImportSelector类

    按住Ctrl点击查看AutoConfigurationImportSelector源码

    public String[] selectImports(AnnotationMetadata annotationMetadata) {
            ... ... ...
            List<String> configurations = getCandidateConfigurations(annotationMetadata,
                                                                       attributes);
            configurations = removeDuplicates(configurations);
            Set<String> exclusions = getExclusions(annotationMetadata, attributes);
            checkExcludedClasses(configurations, exclusions);
            configurations.removeAll(exclusions);
            configurations = filter(configurations, autoConfigurationMetadata);
            fireAutoConfigurationImportEvents(configurations, exclusions);
            return StringUtils.toStringArray(configurations);
    }
    
    
    protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
    			AnnotationAttributes attributes) {
    		List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
    				getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
    		
    		return configurations;
    }
    
    

    其中,SpringFactoriesLoader.loadFactoryNames 方法的作用就是从META-INF/spring.factories文件中读取指定类对应的类名称列表

    spring.factories 文件中有关自动配置的配置信息如下:

    ... ... ...
    
    org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,
    org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,
    org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,
    org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,
    org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,
    org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,
    
    ... ... ...
    

    上面配置文件存在大量的以Configuration为结尾的类名称,这些类就是存有自动配置信息的类,而SpringApplication在获取这些类名后再加载

    我们以ServletWebServerFactoryAutoConfiguration为例来分析源码:

    @Configuration
    @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
    @ConditionalOnClass(ServletRequest.class)
    @ConditionalOnWebApplication(type = Type.SERVLET)
    @EnableConfigurationProperties(ServerProperties.class)
    @Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
    		ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
    		ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
    		ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
    public class ServletWebServerFactoryAutoConfiguration {
    	... ... ...
    }
    
    

    其中,

    @EnableConfigurationProperties(ServerProperties.class) 代表加载ServerProperties服务器配置属性类

    进入ServerProperties.class源码如下:

    @ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
    public class ServerProperties {
    
    	/**
    	 * Server HTTP port.
    	 */
    	private Integer port;
    
    	/**
    	 * Network address to which the server should bind.
    	 */
    	private InetAddress address;
      
      	... ... ...
      
    }
    

    其中,

    prefix = "server" 表示SpringBoot配置文件中的前缀,SpringBoot会将配置文件中以server开始的属性映射到该类的字段中。映射关系如下:

    二、SpringBoot的配置文件

    2.1 SpringBoot配置文件类型

    2.1.1 SpringBoot配置文件类型和作用

    SpringBoot是基于约定的,所以很多配置都有默认值,但如果想使用自己的配置替换默认配置的话,就可以使用application.properties或者application.yml(application.yaml)进行配置。

    SpringBoot默认会从Resources目录下加载application.properties或application.yml(application.yaml)文件

    其中,application.properties文件是键值对类型的文件,之前一直在使用,所以此处不在对properties文件的格式进行阐述。除了properties文件外,SpringBoot还可以使用yml文件进行配置,下面对yml文件进行讲解。

    2.1.2 application.yml配置文件

    2.1.2.1 yml配置文件简介

    YML文件格式是YAML (YAML Aint Markup Language)编写的文件格式,YAML是一种直观的能够被电脑识别的的数据数据序列化格式,并且容易被人类阅读,容易和脚本语言交互的,可以被支持YAML库的不同的编程语言程序导入,比如: C/C++, Ruby, Python, Java, Perl, C#, PHP等。YML文件是以数据为核心的,比传统的xml方式更加简洁。

    YML文件的扩展名可以使用.yml或者.yaml。

    2.1.2.2 yml配置文件的语法

    2.1.2.2.1 配置普通数据
    • 语法: key: value

    • 示例代码:

    • name: haohao
      
    • 注意:value之前有一个空格

    2.1.2.2.2 配置对象数据
    • 语法:

      ​ key:

      ​ key1: value1

      ​ key2: value2

      ​ 或者:

      ​ key: {key1: value1,key2: value2}

    • 示例代码:

    • person:
        name: haohao
        age: 31
        addr: beijing
      
      #或者
      
      person: {name: haohao,age: 31,addr: beijing}
      
    • 注意:key1前面的空格个数不限定,在yml语法中,相同缩进代表同一个级别

    2.1.2.2.2 配置Map数据

    同上面的对象写法

    2.1.2.2.3 配置数组(List、Set)数据
    • 语法:

      ​ key:

      ​ - value1

      ​ - value2

      或者:

      ​ key: [value1,value2]

    • 示例代码:

    • city:
        - beijing
        - tianjin
        - shanghai
        - chongqing
        
      #或者
      
      city: [beijing,tianjin,shanghai,chongqing]
      
      #集合中的元素是对象形式
      student:
        - name: zhangsan
          age: 18
          score: 100
        - name: lisi
          age: 28
          score: 88
        - name: wangwu
          age: 38
          score: 90
      
    • 注意:value1与之间的 - 之间存在一个空格

    2.1.3 SpringBoot配置信息的查询

    上面提及过,SpringBoot的配置文件,主要的目的就是对配置信息进行修改的,但在配置时的key从哪里去查询呢?我们可以查阅SpringBoot的官方文档

    文档URL:https://docs.spring.io/spring-boot/docs/2.0.1.RELEASE/reference/htmlsingle/#common-application-properties

    常用的配置摘抄如下:

    # QUARTZ SCHEDULER (QuartzProperties)
    spring.quartz.jdbc.initialize-schema=embedded # Database schema initialization mode.
    spring.quartz.jdbc.schema=classpath:org/quartz/impl/jdbcjobstore/tables_@@platform@@.sql # Path to the SQL file to use to initialize the database schema.
    spring.quartz.job-store-type=memory # Quartz job store type.
    spring.quartz.properties.*= # Additional Quartz Scheduler properties.
    
    # ----------------------------------------
    # WEB PROPERTIES
    # ----------------------------------------
    
    # EMBEDDED SERVER CONFIGURATION (ServerProperties)
    server.port=8080 # Server HTTP port.
    server.servlet.context-path= # Context path of the application.
    server.servlet.path=/ # Path of the main dispatcher servlet.
    
    # HTTP encoding (HttpEncodingProperties)
    spring.http.encoding.charset=UTF-8 # Charset of HTTP requests and responses. Added to the "Content-Type" header if not set explicitly.
    
    # JACKSON (JacksonProperties)
    spring.jackson.date-format= # Date format string or a fully-qualified date format class name. For instance, `yyyy-MM-dd HH:mm:ss`.
    
    # SPRING MVC (WebMvcProperties)
    spring.mvc.servlet.load-on-startup=-1 # Load on startup priority of the dispatcher servlet.
    spring.mvc.static-path-pattern=/** # Path pattern used for static resources.
    spring.mvc.view.prefix= # Spring MVC view prefix.
    spring.mvc.view.suffix= # Spring MVC view suffix.
    
    # DATASOURCE (DataSourceAutoConfiguration & DataSourceProperties)
    spring.datasource.driver-class-name= # Fully qualified name of the JDBC driver. Auto-detected based on the URL by default.
    spring.datasource.password= # Login password of the database.
    spring.datasource.url= # JDBC URL of the database.
    spring.datasource.username= # Login username of the database.
    
    # JEST (Elasticsearch HTTP client) (JestProperties)
    spring.elasticsearch.jest.password= # Login password.
    spring.elasticsearch.jest.proxy.host= # Proxy host the HTTP client should use.
    spring.elasticsearch.jest.proxy.port= # Proxy port the HTTP client should use.
    spring.elasticsearch.jest.read-timeout=3s # Read timeout.
    spring.elasticsearch.jest.username= # Login username.
    
    

    我们可以通过配置application.poperties 或者 application.yml 来修改SpringBoot的默认配置

    例如:

    application.properties文件

    server.port=8888
    server.servlet.context-path=demo
    

    application.yml文件

    server:
      port: 8888
      servlet:
        context-path: /demo
    

    2.2 配置文件与配置类的属性映射方式

    2.2.1 使用注解@Value映射

    我们可以通过@Value注解将配置文件中的值映射到一个Spring管理的Bean的字段上

    例如:

    application.properties配置如下:

    person:
      name: zhangsan
      age: 18
    

    或者,application.yml配置如下:

    person:
      name: zhangsan
      age: 18
    

    实体Bean代码如下:

    @Controller
    public class QuickStartController {
    
        @Value("${person.name}")
        private String name;
        @Value("${person.age}")
        private Integer age;
    
    
        @RequestMapping("/quick")
        @ResponseBody
        public String quick(){
            return "springboot 访问成功! name="+name+",age="+age;
        }
    
    }
    

    浏览器访问地址:http://localhost:8080/quick 结果如下:

    2.2.2 使用注解@ConfigurationProperties映射

    通过注解@ConfigurationProperties(prefix="配置文件中的key的前缀")可以将配置文件中的配置自动与实体进行映射

    application.properties配置如下:

    person:
      name: zhangsan
      age: 18
    

    或者,application.yml配置如下:

    person:
      name: zhangsan
      age: 18
    

    实体Bean代码如下:

    @Controller
    @ConfigurationProperties(prefix = "person")
    public class QuickStartController {
    
        private String name;
        private Integer age;
    
        @RequestMapping("/quick")
        @ResponseBody
        public String quick(){
            return "springboot 访问成功! name="+name+",age="+age;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    }
    

    浏览器访问地址:http://localhost:8080/quick

    注意:使用@ConfigurationProperties方式可以进行配置文件与实体字段的自动映射,但需要字段必须提供set方法才可以,而使用@Value注解修饰的字段不需要提供set方法

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  • 原文地址:https://www.cnblogs.com/whgk/p/12148728.html
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