Spring boot application.properties reuse values

Question

My question seems pretty simple but I could not find a way to implement it.

Consider the following case:

prop1 = value1
prop2 = value2
prop3 = value3

prop4 = value2     (Value same as prop2)
prop5 = value3     (Value same as prop3)

How to reuse value 2 and 3 (these are actually database specific properties) as I want the user to provide it only once and not repeat it.

Thanks.

Case 1: I would elaborate my case as below: I have two properties file - application.properties and quartz.properties.

application.properties:

prop1 = value1
prop2 = value2
prop3 = value3

quartz.properties

prop4 = value2     (Value same as prop2)
prop5 = value3     (Value same as prop3)

Please note: I cannot merge the contents of the two properties files and they are put separately for a reason.

In normal scenario I expected ${} to work but it doesn't work when the properties are in two different files I guess.

Case 2: [Simple scenario] I tried using just one application.properties. But even then I am not able to reuse the property values in same property file.

My pom.xml

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

    <groupId>com.abc</groupId>
    <artifactId>abc</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>xyz</name>
    <description>xyz</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc6</artifactId>
            <version>11.2.0.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-dbcp2</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jersey</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>


        <!-- Quartz dependencies start -->
        <dependency>
            <groupId>org.quartz-scheduler</groupId>
            <artifactId>quartz</artifactId>
            <version>2.2.1</version>
        </dependency>

        <!-- Includes spring's support classes for quartz -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context-support</artifactId>
        </dependency>

        <!-- Quartz dependencies End -->
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

Answer 1

You can use placeholder for it like this:

prop1 = value1
prop2 = value2
prop3 = value3

prop4 = ${prop2}     (Value same as prop2)
prop5 = ${prop3}     (Value same as prop3)

But note, that this should be in the application.properties so spring is aware of it. In case you want your custom file with properties it would make sense to config PropertyPlaceholderConfigurer, as shown below:

@Configuration
public class PropertyPlaceholderConfigurerConfig {

    @Bean
    public static PropertyPlaceholderConfigurer ppc() throws IOException {
        PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer();
        ppc.setLocations(new ClassPathResource("custom.properties"));
        ppc.setIgnoreUnresolvablePlaceholders(true);
        return ppc;
    }
}

Now you should be abe to:

@Value("${prop4}")
private String someValue;

And it should inject you the right value in your bean.