An issue that does not take effect when a MAVEN project introduces a spring boot dependency

Create a MAVEN project with the following structure:

Among them, the contents of Pom.xml are as follows:

<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.pp.test</groupId>
	<artifactId>properties-test</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>properties-test</name>
	<url>http://maven.apache.org</url>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.5.9.RELEASE</version>
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>

	<build>
		<filters>
			<filter>src/main/profiles/profile-${profiles.active}.properties</filter>
		</filters>
		<resources>
			<resource>
				<filtering>true</filtering>
				<directory>src/main/resources</directory>
			</resource>
		</resources>
	</build>


	<profiles>
		<profile>
			<id>dev</id>
			<properties>
				<profiles.active>dev</profiles.active>
			</properties>
			<activation>
				<activeByDefault>true</activeByDefault>
			</activation>
		</profile>
		<profile>
			<id>test</id>
			<properties>
				<profiles.active>test</profiles.active>
			</properties>
		</profile>
		<profile>
			<id>prod</id>
			<properties>
				<profiles.active>prod</profiles.active>
			</properties>
		</profile>
	</profiles>
</project>

Application.properties File Contents:

Jdbc.driverclassname=${jdbc.driverclassname}
Jdbc.url=${jdbc.url}
Jdbc.username=${jdbc.username}
Jdbc.password=${jdbc.password}

Profile-dev.properties File Contents:

Jdbc.driverclassname=com.mysql.jdbc.driver
jdbc.url=jdbc:mysql:///db_users
jdbc.username=root
Jdbc.password=root

Start the application, error, errors are as follows:

Caused by: java.lang.IllegalArgumentException: Circular placeholder reference 'jdbc.url' in property definitions
	at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:141) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:162) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:126) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:236) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:210) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver.resolveNestedPlaceholders(AbstractPropertyResolver.java:227) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(PropertySourcesPropertyResolver.java:84) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(PropertySourcesPropertyResolver.java:61) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.AbstractEnvironment.getProperty(AbstractEnvironment.java:527) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.context.support.PropertySourcesPlaceholderConfigurer$1.getProperty(PropertySourcesPlaceholderConfigurer.java:132) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.context.support.PropertySourcesPlaceholderConfigurer$1.getProperty(PropertySourcesPlaceholderConfigurer.java:129) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(PropertySourcesPropertyResolver.java:81) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.PropertySourcesPropertyResolver.getPropertyAsRawString(PropertySourcesPropertyResolver.java:71) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver$1.resolvePlaceholder(AbstractPropertyResolver.java:239) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:147) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:126) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:236) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:210) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.context.support.PropertySourcesPlaceholderConfigurer$2.resolveStringValue(PropertySourcesPlaceholderConfigurer.java:172) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.resolveEmbeddedValue(AbstractBeanFactory.java:831) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1086) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	... 17 common frames omitted

The reason for this error is that MAVEN's filtering didn't work, and the placeholder was not replaced. (You can execute the MVN clean package to see if the Application.properties file in the packaged jar has a replacement placeholder)

The reason filtering is invalid is that pom.xml inherits the spring boot dependency

<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId> spring-boot-starter-parent</artifactid>
	<version>1.5.9.RELEASE</version>
</parent >

By opening this dependent pom.xml, we found

Spring boot changes the default placeholder symbol ${} to @

Find out why, then how to solve it is very simple.

Method One:

Add the following content to the Pom.xml

<properties>
	<resource.delimiter>${}</resource.delimiter>
</properties>

Method Two:

Application.properties inside Not ${}, change to @

Jdbc.driverclassname= @jdbc. driverclassname@
jdbc.url= @jdbc. url@
jdbc.username= @jdbc. username@
jdbc.password= @jdbc. password@

Method Three:

Pom.xml does not inherit spring-boot-starter-parent,dependency inside configuration all dependencies and version numbers (after inheriting, a lot of dependencies do not have to write version)

Method Four:

Put

<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId> spring-boot-starter-parent</artifactid>
	<version>1.5.9.RELEASE</version>
</parent >

Change into

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId> org.springframework.boot</groupid>
			<artifactId>spring-boot-starter-web</artifactId>
			<version>1.5.9.RELEASE</version>
			<type>pom</type>
			<scope>import</ scope>
		</dependency>
	</dependencies>
</dependencyManagement>