Java-SpringBoot学习 (三)--SpringBoot配置文件、自动配置原理

SpringBoot配置文件

概述

SpringBoot的配置文件是全局的，当我们创建一个SpringBoot项目时，默认会在resources目录下生成一个application.properties文件。

配置文件的名称是默认是[application]的，也可以为其他名字,但是这样你就要让spring知道这是你的配置文件

• application.properties
• application.yml

虽然默认生成properties文件，但是两种文件格式都支持。

可以有多个配置文件，配置文件可以放置的地方有四个，优先级降低依次

• 当前项目根目录 下的 config 目录下【1】

• 当前项目的根目录下【2】

• resources 目录下的 config 目录下【3】

• resources 目录下【4】
  

【注意】：

• 创建SpringBoot项目时，自动生成的配置文件，默认在resources目录下

• 默认同一目录下，先读取application.properties

• 如果多个配置文件配置了同一个属性，默认使用第一个读取到的

  一般情况下，我们用配置文件来修改SpringBoot自动配置好的一些属性值

编写配置文件

个人觉得YAML比properties更好用一些，看起来也比较明了。所以下面就只说YAML如何编写。

YAML概述

YAML是YAML Ain’t Markup Language【YAML不是一种标记语言】的缩写，但为了强调这种语言以数据做为中心，而不是以置标语言为重点，而用返璞词重新命名。它是一种直观的能够被电脑识别的数据序列化格式，是一个可读性高并且容易被人类阅读，容易和脚本语言交互，用来表达资料序列的编程语言。

它是类似于标准通用标记语言的子集XML的数据描述语言语法比XML简单很多。

​ --------百度百科

对比一下yaml和xml：

//yaml  注意空格
server:
  port: 8087

//xml
<server>
    <port>8087<port>
server>

YAML基础语法

【注意】

• YAML大小写敏感
• yaml以空格的缩进来控制层级关系。
• 只能用空格，不能用 Tab,不要求空格个数，但同一级要左对齐在一列上
• “#” 表示注释
• 字符串 可以不用加引号

<1.常量值：

key:(我是空格)value

number: 1.777
isReal: true
name1: 巴西龟

name2: '巴西龟\n可爱'
#单引号会转义换行符---取出来是：巴西龟\n可爱

name3："巴西龟\n可爱"
#双引号，换行符会换行

<2.对象

user:
  name: a
  age: 27
  sex: 女

流式语法(行内写法)：

user: {name: a,age: 27,sex: 女}

< 3.数组

短横线+空格

hobby:
  - draw
  - song
  - book
 
float：
  - 3.14
  - 5.77
 

流式语法(行内写法)：

hobby: [draw,song,book]

float: [3.14,5.77]

代码实例

<1.pom.xml导入所需依赖

<dependency>
    <groupId>org.springframework.bootgroupId>
    <artifactId>spring-boot-configuration-processorartifactId>
    <optional>trueoptional>
dependency>

<2.编写yml配置文件

server:
  port: 8083

person:
  name: 夏风
  gender: girl
  hobby:
    - sing
    - draw
    - read
  birth: 2019/07/07
  pet:
    type: dog
    name: summer

< 3.编写实体类（记得pojo包放在主程序的 同级目录下）

package com.sehun.springboot.pojo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;
import java.util.Arrays;
import java.util.Date;

/*
@ConfigurationProperties：
将配置文件中配置的每一个属性的值，映射到这个组件中；
告诉SpringBoot将本类中的所有属性和配置文件中相关的配置进行绑定
*/

//注册bean
@Component

@ConfigurationProperties(prefix = "person")
public class Person {
    
    private String name;
    private String gender;
    private String[] hobby;
    private Date birth;
    private Pet pet;

    //此处省略了get/set以及toString（）方法，记得写
}

    



/*
除了使用@ConfigurationProperties，还可以使用@Value来关联配置文件

@Component //注册bean
public class User {
    @Value("${person.name}")
    private String name;
    @Value("girl")
    private String gender;
    ......

}
*/

package com.sehun.springboot.pojo;

public class Pet {
    private String type;
    private String name;

    //此处省略了get/set以及toString（）方法，记得写
}

<4.编写测试类

package com.sehun.springboot;

import com.sehun.springboot.pojo.Person;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringbootPropertiesApplicationTests {

    @Autowired
    Person person = new Person();

    @Test
    public void contextLoads() {
        System.out.println(person);
    }

}

<5.运行结果

扩展

1.加载指定配置文件

@configurationProperties默认从全局配置文件中获取值

@PropertySource可以用来加载指定配置文件

假设你在resources目录下又写了一个配置文件，another.properties,你要在你的实体类上加载它：

@Component 
@PropertySource(value = "classpath:another.properties")
public class Person {
    @Value{"${}"}
    private A a；
        ......
}

2.配置文件占位符

${***}

${random.int}---随机生成一个int型的随机数
${random.value}---随机生成一个32位的字符串
${random.int(10)}---随机生一个[0,10]之间的int型随机数
${person.name}---获取配置文件中已经配置好的属性值
${person.name：apple}---获取配置文件中已经配置好的属性值，name不存在时返回“apple”

例

#将application.yml  改成下面这样，再运行
person:
  gender: ${person.name:apple}

结果：

3.多环境切换

• 多配置文件

  文件名：application-{profile}.properties/yml
  例：
         application-test.properties
         application-run.properties
  激活：
  spring.profiles.active=run
  

• yml的多文档块

  server:
    port: 8081
  spring:
  #选择要激活的文档块
    profiles:
      active: test
  
  ---
  server:
    port: 8082
  #配置环境的名称
  spring:
    profiles: test
  
  ---
  server:
    port: 8083
  #配置环境的名称
  spring:
    profiles: run
  

自动配置原理

看我的上一篇博客就知道，在启动类加载的时候，注解@EnableAutoConfiguration开启自动配置功能

• 点进去看它的源码，有一个AutoConfigurationImportSelector,通过它给容器中导入一些组件，那到底导入了那些组件，继续点进去看这个选择器的源码
• 会发现源码里有一个方法：

public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        } else {
            AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
            AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(autoConfigurationMetadata, annotationMetadata);
            return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
        }
    }

这个方法最后返回一个autoConfigurationEntry

• 继续看autoConfigurationEntry的源码，会发现，这个autoConfigurationEntry来自this.getAutoConfigurationEntry(autoConfigurationMetadata, annotationMetadata)

• 继续追踪getAutoConfigurationEntry的源码，会找到一个值： 【List configurations = this.getCandidateConfigurations(annotationMetadata, attributes);】 意思是，获取候选的位置

• 继续追踪getCandidateConfigurations,会得到一个方法，

  protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
          List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
          Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.");
          return configurations;
      }
  
  protected Class<?> getSpringFactoriesLoaderFactoryClass() {
          return EnableAutoConfiguration.class;
      }
  

• 发现有一个SpringFactoriesLoader.loadFactoryNames（）继续追踪

   public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
          String factoryClassName = factoryClass.getName();
          return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
      }
  

  发现它又调用了loadSpringFactories()方法，继续看这个方法的源码：

  private static Map> loadSpringFactories(@Nullable ClassLoader classLoader) {
          MultiValueMap result = (MultiValueMap)cache.get(classLoader);
          if (result != null) {
              return result;
          } else {
              try {
                  Enumeration urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
                  LinkedMultiValueMap result = new LinkedMultiValueMap();
  
                  while(urls.hasMoreElements()) {
                      URL url = (URL)urls.nextElement();
                      UrlResource resource = new UrlResource(url);
                      Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                      Iterator var6 = properties.entrySet().iterator();
  
                      while(var6.hasNext()) {
                          Entry entry = (Entry)var6.next();
                          String factoryClassName = ((String)entry.getKey()).trim();
                          String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                          int var10 = var9.length;
  
                          for(int var11 = 0; var11 < var10; ++var11) {
                              String factoryName = var9[var11];
                              result.add(factoryClassName, factoryName.trim());
                          }
                      }
                  }
  
                  cache.put(classLoader, result);
                  return result;
              } catch (IOException var13) {
                  throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
              }
          }
      }
  

​ 它去获得了一个资源文件：“META-INF/spring.factories”， 将读取到的资源封装在url中，然后遍历url ， 将这些url文件封装在Properties文件中；最后返回封装好的结果。

我们再往前去看，会发现它的那个ClassLoader参数，就是EnableAutoConfiguration

protected Class<?> getSpringFactoriesLoaderFactoryClass() {
        return EnableAutoConfiguration.class;
    }

• 即从properties中获取到EnableAutoConfiguration.class类（类名）对应的值，然后把他们添加在容器中

总结一下就是：将类路径下 META-INF/spring.factories 里面配置的所有EnableAutoConfiguration的值加入到了容器中；

我们从META-INF/spring.factories把它拿过来：

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityRequestMatcherProviderAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
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,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\
org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer

# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider

• 我们找一个我们熟悉的点进去看看源码，比如org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,

  @Configuration 
  @EnableConfigurationProperties({HttpProperties.class}) 
  
  /*
  **根据不同的条件判断，如果满足指定的条件，整个配置类里面的配置就会生效；
  **这里判断当前应用是否是web应用，如果是，当前配置类生效
  */
  @ConditionalOnWebApplication(
      type = Type.SERVLET
  )
  
  @ConditionalOnClass({CharacterEncodingFilter.class})
  @ConditionalOnProperty(
      prefix = "spring.http.encoding",
      value = {"enabled"},
      matchIfMissing = true
  )
  public class HttpEncodingAutoConfiguration {
      private final Encoding properties;
      public HttpEncodingAutoConfiguration(HttpProperties properties) {
          this.properties = properties.getEncoding();
      }
  
      @Bean
      @ConditionalOnMissingBean 
      public CharacterEncodingFilter characterEncodingFilter() {
          CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
          filter.setEncoding(this.properties.getCharset().name());
          filter.setForceRequestEncoding(this.properties.shouldForce(org.springframework.boot.autoconfigure.http.HttpProperties.Encoding.Type.REQUEST));
          filter.setForceResponseEncoding(this.properties.shouldForce(org.springframework.boot.autoconfigure.http.HttpProperties.Encoding.Type.RESPONSE));
          return filter;
      }
      。。。。。。
  }  
  

  倘若判断配置类生效；这个配置类就会给容器中添加各种组件；这些组件的属性是从对应的properties类中获取的，这些类里面的每一个属性又是和配置文件绑定的；配置文件中能配置的属性都是在xxxxProperties类中封装的。

  我们可以看一下HttpProperties.class的源码

重点拿到：【 prefix = “spring.http”】

然后就可以去配置文件里修改默认属性了，如下图

小提示：

我们加载了很多的配置类，但不是所有的都生效了，那如何知道哪些生效了呢？

在配置文件中启用 debug=true属性；可以让控制台打印自动配置报告，这样我们就可以知道哪些自动配置类生效；