SpringApplication会从以下路径加载所有的application.properties文件：
1、file:./config/（当前目录下的config文件夹）
2、file:./（当前目录）
3、classpath:/config/（classpath下的config目录）
4、classpath:/（classpath根目录）
优先级由上至下。
注意：优先级是指属性最后使用的值，而不是说仅仅扫描优先级高的路径，不是发现了application.properties文件就停止。例如classpath:/config/和file:./config/都存在配置文件，那么加载过程会加载classpath:/config/路径下配置文件的所有属性，然后再加载file:./config/路径下配置文件的属性并替换已有的属性。此外，如果你在相同优先级位置同时有application.properties和application.yml，那么application.yml里面的属性就会覆盖application.properties里的属性。
如果你不想使用application.properties的格式命名配置文件，那么可以通过环境变量spring.config.name来设置文件名称，例如：
$ java -jar myproject.jar --spring.config.name=example-sys.properties此时，要加载的配置文件名为example-sys.properties。除了修改名称，还可以使用 spring.config.location 来添加要加载的路径。例如我们以这个命令启动JVM：$ java -jar myapp.jar --spring.config.location=classpath:/myconfig/,file:./myconfig/
那么加载application.properties文件的路径以及优先级会变为：
1、file:./myconfig/
2、classpath:/myconfig/
3、file:./config/
4、file:./
5、classpath:/config/
6、classpath:/
spring.config.location环境变量也可以直接设定到加载文件的名称，例如：--spring.config.location=classpath:/default.properties
通常情况下这样做并没有太大问题，但是结合到Profiles文件特性时，会导致无法根据标记加载对应的Profiles文件。
由于配置文件路径和配置文件名称在容器未启动时就需要声明，所以最好在OS的环境变量、JVM的系统环境变量或命令行参数就设定它。
注：
"file:"文件路径前缀的相对路径根目录是 用户当前目录(即用户运行jar包时的当前目录)
"classpath:"文件路径前缀的相对路径根目录是 jar包内classes文件夹
classpath 优先本项目class路径查找，没有的话依次在其他jar包中class路径查找，找到第一个匹配的为止
classpath* 加载到所有class路径下的配置文件，包括jar包的class路径下，最终加载所有匹配的
file 通过URL加载，来源为文件系统（注意文件读取权限）
http 通过URL加载，来源为网络
(none) 根据 ApplicationContext 进行判断（这个我没试过）
classpath
<context:property-placeholder location="classpath:system.properties" />
举个栗子：A项目中resources中存在system.properties，B项目中resources中也存在system.properties。A项目以jar包形式引入B项目。此时A项目spring配置classpath:system.properties加载到的是A项目自己的system.properties。但是如果A项目resources中没有system.properties则最终结果加载到的是B.jar中的system.properties
classpath*
<context:property-placeholder location="classpath*:system.properties" />
举个栗子：A项目中resources中存在system.properties，B项目中resources中也存在system.properties。A项目以jar包形式引入B项目。此时A项目spring配置classpath*:system.properties加载到的是A和B的system.properties
如下图（我是引入的两个jar都有同名配置文件）：
这里大家可能会有疑问，同时引入了两个同名配置文件，如果两个同名配置文件中有同样的配置，比如:
A项目system.properties
milo=a
milo1=a
B项目system.properties
milo=b
milo1=b
那么最终引用的是哪个？我这边最终实验结果是根据spring加载顺序倒叙加载，直到找到匹配的值。而且值与值之间不影响，每次都按加载顺序倒叙查找。即：如果spring加载顺序为A->B ,那么最终取到的值为：milo=b milo1=b。而且spring在取milo和milo1时都是按照spring加载顺序倒叙取得。大家可以通过三个配置文件情况做下试验。对spring熟悉的同学也可找下源码看一下。
附：
application.properties参数详解
# ----------------------------------------
# CORE PROPERTIES
# ---------------------------------------- # SPRING 相关配置 (ConfigFileApplicationListener)
spring.config.name= # config file name (default to 'application')
spring.config.location= # location of config file # profile相关配置
spring.profiles= # comma list of active profiles # 系统配置相关参数 (SpringApplication)
spring.main.sources=
spring.main.web-environment= # detect by default
spring.main.show-banner=true
spring.main....= # see class for all properties # 日志配置相关参数
logging.path=/var/logs
logging.file=myapp.log
logging.config= # IDENTITY (ContextIdApplicationContextInitializer)
spring.application.name=
spring.application.index= # tomcat相关配置参数 (ServerProperties)
server.port=8080
server.address= # bind to a specific NIC
server.session-timeout= # session timeout in seconds
server.context-path= # the context path, defaults to '/'
server.servlet-path= # the servlet path, defaults to '/'
server.tomcat.access-log-pattern= # log pattern of the access log
server.tomcat.access-log-enabled=false # is access logging enabled
server.tomcat.protocol-header=x-forwarded-proto # ssl forward headers
server.tomcat.remote-ip-header=x-forwarded-for
server.tomcat.basedir=/tmp # base dir (usually not needed, defaults to tmp)
server.tomcat.background-processor-delay=30; # in seconds
server.tomcat.max-threads = 0 # number of threads in protocol handler
server.tomcat.uri-encoding = UTF-8 # character encoding to use for URL decoding # springmvc相关配置参数 (HttpMapperProperties)
http.mappers.json-pretty-print=false # pretty print JSON
http.mappers.json-sort-keys=false # sort keys
spring.mvc.locale= # set fixed locale, e.g. en_UK
spring.mvc.date-format= # set fixed date format, e.g. dd/MM/yyyy
spring.mvc.message-codes-resolver-format= # PREFIX_ERROR_CODE / POSTFIX_ERROR_CODE
spring.view.prefix= # MVC view prefix
spring.view.suffix= # ... and suffix
spring.resources.cache-period= # cache timeouts in headers sent to browser
spring.resources.add-mappings=true # if default mappings should be added # thymeleaf相关配置参数 (ThymeleafAutoConfiguration)
spring.thymeleaf.prefix=classpath:/templates/
spring.thymeleaf.suffix=.html
spring.thymeleaf.mode=HTML5
spring.thymeleaf.encoding=UTF-8
spring.thymeleaf.content-type=text/html # ;charset=<encoding> is added
spring.thymeleaf.cache=true # set to false for hot refresh # freemark相关配置参数 (FreeMarkerAutoConfiguration)
spring.freemarker.allowRequestOverride=false
spring.freemarker.allowSessionOverride=false
spring.freemarker.cache=true
spring.freemarker.checkTemplateLocation=true
spring.freemarker.contentType=text/html
spring.freemarker.exposeRequestAttributes=false
spring.freemarker.exposeSessionAttributes=false
spring.freemarker.exposeSpringMacroHelpers=false
spring.freemarker.prefix=
spring.freemarker.requestContextAttribute=
spring.freemarker.settings.*=
spring.freemarker.suffix=.ftl
spring.freemarker.templateEncoding=UTF-8
spring.freemarker.templateLoaderPath=classpath:/templates/
spring.freemarker.viewNames= # whitelist of view names that can be resolved # groovy模板相关配置参数 (GroovyTemplateAutoConfiguration)
spring.groovy.template.allowRequestOverride=false
spring.groovy.template.allowSessionOverride=false
spring.groovy.template.cache=true
spring.groovy.template.configuration.*= # See Groovy's TemplateConfiguration
spring.groovy.template.contentType=text/html
spring.groovy.template.prefix=classpath:/templates/
spring.groovy.template.suffix=.tpl
spring.groovy.template.templateEncoding=UTF-8
spring.groovy.template.viewNames= # whitelist of view names that can be resolved # velocity模板相关配置参数 (VelocityAutoConfiguration)
spring.velocity.allowRequestOverride=false
spring.velocity.allowSessionOverride=false
spring.velocity.cache=true
spring.velocity.checkTemplateLocation=true
spring.velocity.contentType=text/html
spring.velocity.dateToolAttribute=
spring.velocity.exposeRequestAttributes=false
spring.velocity.exposeSessionAttributes=false
spring.velocity.exposeSpringMacroHelpers=false
spring.velocity.numberToolAttribute=
spring.velocity.prefix=
spring.velocity.properties.*=
spring.velocity.requestContextAttribute=
spring.velocity.resourceLoaderPath=classpath:/templates/
spring.velocity.suffix=.vm
spring.velocity.templateEncoding=UTF-8
spring.velocity.viewNames= # whitelist of view names that can be resolved # INTERNATIONALIZATION (MessageSourceAutoConfiguration)
spring.messages.basename=messages
spring.messages.cacheSeconds=-1
spring.messages.encoding=UTF-8 # 安全相关配置参数 (SecurityProperties)
security.user.name=user # login username
security.user.password= # login password
security.user.role=USER # role assigned to the user
security.require-ssl=false # advanced settings ...
security.enable-csrf=false
security.basic.enabled=true
security.basic.realm=Spring
security.basic.path= # /**
security.headers.xss=false
security.headers.cache=false
security.headers.frame=false
security.headers.contentType=false
security.headers.hsts=all # none / domain / all
security.sessions=stateless # always / never / if_required / stateless
security.ignored=false # 数据源相关配置参数(DataSourceAutoConfiguration & DataSourceProperties)
spring.datasource.name= # name of the data source
spring.datasource.initialize=true # populate using data.sql
spring.datasource.schema= # a schema (DDL) script resource reference
spring.datasource.data= # a data (DML) script resource reference
spring.datasource.platform= # the platform to use in the schema resource (schema-${platform}.sql)
spring.datasource.continueOnError=false # continue even if can't be initialized
spring.datasource.separator=; # statement separator in SQL initialization scripts
spring.datasource.driverClassName= # JDBC Settings...
spring.datasource.url=
spring.datasource.username=
spring.datasource.password=
spring.datasource.max-active=100 # Advanced configuration...
spring.datasource.max-idle=8
spring.datasource.min-idle=8
spring.datasource.initial-size=10
spring.datasource.validation-query=
spring.datasource.test-on-borrow=false
spring.datasource.test-on-return=false
spring.datasource.test-while-idle=
spring.datasource.time-between-eviction-runs-millis=
spring.datasource.min-evictable-idle-time-millis=
spring.datasource.max-wait-millis= # mongdb相关配置参数 (MongoProperties)
spring.data.mongodb.host= # the db host
spring.data.mongodb.port=27017 # the connection port (defaults to 27107)
spring.data.mongodb.uri=mongodb://localhost/test # connection URL
spring.data.mongo.repositories.enabled=true # if spring data repository support is enabled # springDataJPA相关配置参数(JpaBaseConfiguration, HibernateJpaAutoConfiguration)
spring.jpa.properties.*= # properties to set on the JPA connection
spring.jpa.openInView=true
spring.jpa.show-sql=true
spring.jpa.database-platform=
spring.jpa.database=
spring.jpa.generate-ddl=false # ignored by Hibernate, might be useful for other vendors
spring.jpa.hibernate.naming-strategy= # naming classname
spring.jpa.hibernate.ddl-auto= # defaults to create-drop for embedded dbs
spring.data.jpa.repositories.enabled=true # if spring data repository support is enabled # solr相关配置参数(SolrProperties})
spring.data.solr.host=http://127.0.0.1:8983/solr
spring.data.solr.zkHost=
spring.data.solr.repositories.enabled=true # if spring data repository support is enabled # elasticsearch相关配置参数(ElasticsearchProperties})
spring.data.elasticsearch.cluster-name= # The cluster name (defaults to elasticsearch)
spring.data.elasticsearch.cluster-nodes= # The address(es) of the server node (comma-separated; if not specified starts a client node)
spring.data.elasticsearch.local=true # if local mode should be used with client nodes
spring.data.elasticsearch.repositories.enabled=true # if spring data repository support is enabled # flyway相关配置参数(FlywayProperties)
flyway.locations=classpath:db/migrations # locations of migrations scripts
flyway.schemas= # schemas to update
flyway.initVersion= 1 # version to start migration
flyway.prefix=V
flyway.suffix=.sql
flyway.enabled=true
flyway.url= # JDBC url if you want Flyway to create its own DataSource
flyway.user= # JDBC username if you want Flyway to create its own DataSource
flyway.password= # JDBC password if you want Flyway to create its own DataSource # liquibase相关配置参数(LiquibaseProperties)
liquibase.change-log=classpath:/db/changelog/db.changelog-master.yaml
liquibase.contexts= # runtime contexts to use
liquibase.default-schema= # default database schema to use
liquibase.drop-first=false
liquibase.enabled=true # JMX
spring.jmx.enabled=true # Expose MBeans from Spring # rabbitmq相关配置参数(RabbitProperties)
spring.rabbitmq.host= # connection host
spring.rabbitmq.port= # connection port
spring.rabbitmq.addresses= # connection addresses (e.g. myhost:9999,otherhost:1111)
spring.rabbitmq.username= # login user
spring.rabbitmq.password= # login password
spring.rabbitmq.virtualhost=
spring.rabbitmq.dynamic= # redis相关配置参数(RedisProperties)
spring.redis.host=localhost # server host
spring.redis.password= # server password
spring.redis.port=6379 # connection port
spring.redis.pool.max-idle=8 # pool settings ...
spring.redis.pool.min-idle=0
spring.redis.pool.max-active=8
spring.redis.pool.max-wait=-1 # activemq相关配置参数(ActiveMQProperties)
spring.activemq.broker-url=tcp://localhost:61616 # connection URL
spring.activemq.user=
spring.activemq.password=
spring.activemq.in-memory=true # broker kind to create if no broker-url is specified
spring.activemq.pooled=false # hornetq相关配置参数(HornetQProperties)
spring.hornetq.mode= # connection mode (native, embedded)
spring.hornetq.host=localhost # hornetQ host (native mode)
spring.hornetq.port=5445 # hornetQ port (native mode)
spring.hornetq.embedded.enabled=true # if the embedded server is enabled (needs hornetq-jms-server.jar)
spring.hornetq.embedded.serverId= # auto-generated id of the embedded server (integer)
spring.hornetq.embedded.persistent=false # message persistence
spring.hornetq.embedded.data-directory= # location of data content (when persistence is enabled)
spring.hornetq.embedded.queues= # comma separate queues to create on startup
spring.hornetq.embedded.topics= # comma separate topics to create on startup
spring.hornetq.embedded.cluster-password= # customer password (randomly generated by default) # JMS (JmsProperties)
spring.jms.pub-sub-domain= # false for queue (default), true for topic # springbatch相关配置参数(BatchDatabaseInitializer)
spring.batch.job.names=job1,job2
spring.batch.job.enabled=true
spring.batch.initializer.enabled=true
spring.batch.schema= # batch schema to load # aop相关配置参数
spring.aop.auto=
spring.aop.proxy-target-class= # FILE ENCODING (FileEncodingApplicationListener)
spring.mandatory-file-encoding=false # SPRING SOCIAL (SocialWebAutoConfiguration)
spring.social.auto-connection-views=true # Set to true for default connection views or false if you provide your own # SPRING SOCIAL FACEBOOK (FacebookAutoConfiguration)
spring.social.facebook.app-id= # your application's Facebook App ID
spring.social.facebook.app-secret= # your application's Facebook App Secret # SPRING SOCIAL LINKEDIN (LinkedInAutoConfiguration)
spring.social.linkedin.app-id= # your application's LinkedIn App ID
spring.social.linkedin.app-secret= # your application's LinkedIn App Secret # SPRING SOCIAL TWITTER (TwitterAutoConfiguration)
spring.social.twitter.app-id= # your application's Twitter App ID
spring.social.twitter.app-secret= # your application's Twitter App Secret # SPRING MOBILE SITE PREFERENCE (SitePreferenceAutoConfiguration)
spring.mobile.sitepreference.enabled=true # enabled by default # SPRING MOBILE DEVICE VIEWS (DeviceDelegatingViewResolverAutoConfiguration)
spring.mobile.devicedelegatingviewresolver.enabled=true # disabled by default
spring.mobile.devicedelegatingviewresolver.normalPrefix=
spring.mobile.devicedelegatingviewresolver.normalSuffix=
spring.mobile.devicedelegatingviewresolver.mobilePrefix=mobile/
spring.mobile.devicedelegatingviewresolver.mobileSuffix=
spring.mobile.devicedelegatingviewresolver.tabletPrefix=tablet/
spring.mobile.devicedelegatingviewresolver.tabletSuffix= # ----------------------------------------
# ACTUATOR PROPERTIES
# ---------------------------------------- # MANAGEMENT HTTP SERVER (ManagementServerProperties)
management.port= # defaults to 'server.port'
management.address= # bind to a specific NIC
management.contextPath= # default to '/' # ENDPOINTS (AbstractEndpoint subclasses)
endpoints.autoconfig.id=autoconfig
endpoints.autoconfig.sensitive=true
endpoints.autoconfig.enabled=true
endpoints.beans.id=beans
endpoints.beans.sensitive=true
endpoints.beans.enabled=true
endpoints.configprops.id=configprops
endpoints.configprops.sensitive=true
endpoints.configprops.enabled=true
endpoints.configprops.keys-to-sanitize=password,secret
endpoints.dump.id=dump
endpoints.dump.sensitive=true
endpoints.dump.enabled=true
endpoints.env.id=env
endpoints.env.sensitive=true
endpoints.env.enabled=true
endpoints.health.id=health
endpoints.health.sensitive=false
endpoints.health.enabled=true
endpoints.info.id=info
endpoints.info.sensitive=false
endpoints.info.enabled=true
endpoints.metrics.id=metrics
endpoints.metrics.sensitive=true
endpoints.metrics.enabled=true
endpoints.shutdown.id=shutdown
endpoints.shutdown.sensitive=true
endpoints.shutdown.enabled=false
endpoints.trace.id=trace
endpoints.trace.sensitive=true
endpoints.trace.enabled=true # MVC ONLY ENDPOINTS
endpoints.jolokia.path=jolokia
endpoints.jolokia.sensitive=true
endpoints.jolokia.enabled=true # when using Jolokia
endpoints.error.path=/error # JMX ENDPOINT (EndpointMBeanExportProperties)
endpoints.jmx.enabled=true
endpoints.jmx.domain= # the JMX domain, defaults to 'org.springboot'
endpoints.jmx.unique-names=false
endpoints.jmx.enabled=true
endpoints.jmx.staticNames= # JOLOKIA (JolokiaProperties)
jolokia.config.*= # See Jolokia manual # REMOTE SHELL
shell.auth=simple # jaas, key, simple, spring
shell.command-refresh-interval=-1
shell.command-path-pattern= # classpath*:/commands/**, classpath*:/crash/commands/**
shell.config-path-patterns= # classpath*:/crash/*
shell.disabled-plugins=false # don't expose plugins
shell.ssh.enabled= # ssh settings ...
shell.ssh.keyPath=
shell.ssh.port=
shell.telnet.enabled= # telnet settings ...
shell.telnet.port=
shell.auth.jaas.domain= # authentication settings ...
shell.auth.key.path=
shell.auth.simple.user.name=
shell.auth.simple.user.password=
shell.auth.spring.roles= # GIT INFO
spring.git.properties= # resource ref to generated git info properties file
参考文献：
SpringBoot配置文件application.properties参数详解
Spring Boot学习总结（13）——Spring Boot加载application.properties配置文件顺序规则