1. Introduction
Reading external properties in a maven project is useful when accessing secure credential configuration, or logging settings, etc. In this article, I will demonstrate how to read an external properties file in a Maven project.
2. Setup
In this step, I will create a maven project in an Eclipse IDE.
2.1. Maven Project Folder Structure
This generated project follows the Maven project folder structure.
- The external properties file is stored in the “
external-config” folder in the project root directory. - The
maven-resources-pluginfilters files in thesrc/main/resourcesdirectory and places the result under${project.build.outputDirectory}/filtered-result.
2.2 External Properties
The “external-config” folder in the project root is added to store the external properties. There are four properties defined: “my.custom.property“, “server.log“, “database.login“, and “apikey“.
external.properties
my.custom.property=This is a custom value under external-config/external.properties server.log=server log location different at environment database.login=database credentials should not in source code apikey=apikey should not in source repository
2.3 Result.txt
The “src/main/resource/result.txt” file contains the properties defined in the external.properties file. The property’s value will be replaced when the “process-resources” task is executed.
result.txt
Properties from pom.xml: ${greeting}
-----------------------------
External Properties: ${my.custom.property}
server log location: ${server.log}
database credentials: ${database.login}
apikey: ${apikey}
3. POM.XML File
In this step, I will update the generated pom.xml by adding two build plugins: maven-resource-plugin and properties-maven-plugin to read the “my.custom.property“, “server.log“, “database.login“, and “apikey” properties from the external file and the result.txt is updated with their values.
pom.xml
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.zheng.demo</groupId>
<artifactId>maven-external-properties</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>maven-external-properties</name>
<description>demo for maven external properties</description>
<packaging>jar</packaging>
<properties>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
<greeting>Hi there, how are you</greeting>
<user.properties.file>external-config/external.properties</user.properties.file>
</properties>
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<filtering>true</filtering>
</resource>
</resources>
<plugins>
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.3.1</version>
<configuration>
<outputDirectory>
${project.build.outputDirectory}/filtered-result</outputDirectory>
</configuration>
</plugin>
<!-- Properties Maven Plugin to load external properties -->
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>properties-maven-plugin</artifactId>
<version>1.2.1</version>
<executions>
<execution>
<phase>initialize</phase> <!-- This phase reads
properties -->
<goals>
<goal>read-project-properties</goal>
</goals>
<configuration>
<files>
<file>${user.properties.file}</file> <!--
Path to
external properties file -->
</files>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
- Line 16: defines the
greetingproperty with the"Hi there, how are you"value. - Line 17: defines the
user.propertiesfile with theexternal-config/external.propertiesvalue. - Line 24: enable the resource filtering.
- Line 29: configure
maven-resources-pluginfor the build process. - Line 40: configure
properties-maven-pluginfor the build process. - Line 51: access the external file location via
user.properties.file.
4. Read External Properties Demo
In this step, I will execute the mvn clean install command and capture the output.
mvn clean install output
C:\MaryTools\workspace\maven-external-properties>mvn clean install [INFO] Scanning for projects... [INFO] [INFO] --------------< org.zheng.demo:maven-external-properties >-------------- [INFO] Building maven-external-properties 0.0.1-SNAPSHOT [INFO] from pom.xml [INFO] --------------------------------[ jar ]--------------------------------- [INFO] [INFO] --- clean:3.2.0:clean (default-clean) @ maven-external-properties --- [INFO] Deleting C:\MaryTools\workspace\maven-external-properties\target [INFO] [INFO] --- properties:1.2.1:read-project-properties (default) @ maven-external-properties --- [INFO] Loading 4 properties from File: C:\MaryTools\workspace\maven-external-properties\external-config\external.properties [INFO] [INFO] --- resources:3.3.1:resources (default-resources) @ maven-external-properties --- [WARNING] File encoding has not been set, using platform encoding Cp1252. Build is platform dependent! [WARNING] See https://maven.apache.org/general.html#encoding-warning [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent! [INFO] Copying 1 resource from src\main\resources to target\classes\filtered-result [INFO] [INFO] --- compiler:3.11.0:compile (default-compile) @ maven-external-properties --- [INFO] Nothing to compile - all classes are up to date [INFO] [INFO] --- resources:3.3.1:testResources (default-testResources) @ maven-external-properties --- [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent! [INFO] Copying 0 resource from src\test\resources to target\classes\filtered-result [INFO] [INFO] --- compiler:3.11.0:testCompile (default-testCompile) @ maven-external-properties --- [INFO] Nothing to compile - all classes are up to date [INFO] [INFO] --- surefire:3.2.2:test (default-test) @ maven-external-properties --- [INFO] No tests to run. [INFO] [INFO] --- jar:3.3.0:jar (default-jar) @ maven-external-properties --- [INFO] Building jar: C:\MaryTools\workspace\maven-external-properties\target\maven-external-properties-0.0.1-SNAPSHOT.jar [INFO] [INFO] --- install:3.1.1:install (default-install) @ maven-external-properties --- [INFO] Installing C:\MaryTools\workspace\maven-external-properties\pom.xml to C:\Users\azpm0\.m2\repository\org\zheng\demo\maven-external-properties\0.0.1-SNAPSHOT\maven-external-properties-0.0.1-SNAPSHOT.pom [INFO] Installing C:\MaryTools\workspace\maven-external-properties\target\maven-external-properties-0.0.1-SNAPSHOT.jar to C:\Users\azpm0\.m2\repository\org\zheng\demo\maven-external-properties\0.0.1-SNAPSHOT\maven-external-properties-0.0.1-SNAPSHOT.jar [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESS [INFO] ------------------------------------------------------------------------ [INFO] Total time: 9.652 s [INFO] Finished at: 2025-03-22T12:46:38-05:00 [INFO] ------------------------------------------------------------------------ C:\MaryTools\workspace\maven-external-properties>
- Line 12:
read-project-propertiesreads the properties from the external file. - Line 15:
default-resourcesreplaces the property value and copies it to thefilter-resultfolder. - Line 19: outline the details when copying resources.
4.1 Verify the Result.txt is Updated
In this step, I will verify that property values in the result.txt file are replaced.
repalced result.txt
Properties from pom.xml: Hi there, how are you ----------------------------- External Properties: This is a custom value under external-config/external.properties server log location: server log location different at environment database credentials: database credentials should not in source code apikey: apikey should not in source repository
As expected, the properties are replaced with the value in the external.properties file.
5. Read External Properties via Argument
In this step, I will prepare user.properties in a different location:
user.properteies
my.custom.property=This is a custom value under user.properties server.log=server.log database.login=unknown apikey=guess
I will execute the mvn clean install and overwrite the external property file.
mvn clean install -Dgreeting=Mary -Duser.properties.file=C:\MaryTools\workspace\config\props\user.properties
C:\MaryTools\workspace\maven-external-properties>mvn clean install -Dgreeting=Mary -Duser.properties.file=C:\MaryTools\workspace\config\props\user.properties [INFO] Scanning for projects... [INFO] [INFO] --------------< org.zheng.demo:maven-external-properties >-------------- [INFO] Building maven-external-properties 0.0.1-SNAPSHOT [INFO] from pom.xml [INFO] --------------------------------[ jar ]--------------------------------- [INFO] [INFO] --- clean:3.2.0:clean (default-clean) @ maven-external-properties --- [INFO] Deleting C:\MaryTools\workspace\maven-external-properties\target [INFO] [INFO] --- properties:1.2.1:read-project-properties (default) @ maven-external-properties --- [INFO] Loading 4 properties from File: C:\MaryTools\workspace\config\props\user.properties [INFO] [INFO] --- resources:3.3.1:resources (default-resources) @ maven-external-properties --- [WARNING] File encoding has not been set, using platform encoding Cp1252. Build is platform dependent! [WARNING] See https://maven.apache.org/general.html#encoding-warning [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent! [INFO] Copying 1 resource from src\main\resources to target\classes\filtered-result [INFO] [INFO] --- compiler:3.11.0:compile (default-compile) @ maven-external-properties --- [INFO] Nothing to compile - all classes are up to date [INFO] [INFO] --- resources:3.3.1:testResources (default-testResources) @ maven-external-properties --- [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent! [INFO] Copying 0 resource from src\test\resources to target\classes\filtered-result [INFO] [INFO] --- compiler:3.11.0:testCompile (default-testCompile) @ maven-external-properties --- [INFO] Nothing to compile - all classes are up to date [INFO] [INFO] --- surefire:3.2.2:test (default-test) @ maven-external-properties --- [INFO] No tests to run. [INFO] [INFO] --- jar:3.3.0:jar (default-jar) @ maven-external-properties --- [INFO] Building jar: C:\MaryTools\workspace\maven-external-properties\target\maven-external-properties-0.0.1-SNAPSHOT.jar [INFO] [INFO] --- install:3.1.1:install (default-install) @ maven-external-properties --- [INFO] Installing C:\MaryTools\workspace\maven-external-properties\pom.xml to C:\Users\azpm0\.m2\repository\org\zheng\demo\maven-external-properties\0.0.1-SNAPSHOT\maven-external-properties-0.0.1-SNAPSHOT.pom [INFO] Installing C:\MaryTools\workspace\maven-external-properties\target\maven-external-properties-0.0.1-SNAPSHOT.jar to C:\Users\azpm0\.m2\repository\org\zheng\demo\maven-external-properties\0.0.1-SNAPSHOT\maven-external-properties-0.0.1-SNAPSHOT.jar [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESS [INFO] ------------------------------------------------------------------------ [INFO] Total time: 1.348 s [INFO] Finished at: 2025-03-22T12:54:22-05:00 [INFO] ------------------------------------------------------------------------ C:\MaryTools\workspace\maven-external-properties>
- Line 1: the “
-Dgreeting=Mary” overwrites thegreetingproperty value defined in thepom.xml - Line 1: the “
-Duser.properties.file=C:\MaryTools\workspace\config\props\user.properties” overwrites the external properties with a different external file.
5.1 Verify the Result.txt is Updated
In this step, I will verify that property values in the result.txt are replaced.
replaced result.txt
Properties from pom.xml: Mary ----------------------------- External Properties: This is a custom value under user.properties server log location: server.log database credentials: unknown apikey: guess
As expected, the properties are replaced with the values in the user.properties file.
6. Conclusion
In this article, I demonstrated how to read external properties by leveraging the properties Maven plugin. It helps manage environment-specific builds, ensuring projects remain clean, maintainable, and adaptable.
7. Download
This was an example of a maven project that used properties-maven-plugin to read external properties.
Download
You can download the full source code of this example here: Read an External Properties File in Maven
You can download the full source code of this example here: Read an External Properties File in Maven
