How to get value from gradle.properties in .class file at the time of build

Question

I would like to get a property value from Gradle.properties in Java class. In Java, the value should be replaced at build time, and in the .jar(.class) file the value will come but not in a .java file. So that we can change the value directly in gradle.properties and no need to change the code. Is it possible to achieve?

Answer 1

It would be easier to answer if you told your specific use case. Also it would help to know your application, for example is it a Spring (Boot) app? In that case it would probably make more sense to use Spring Profiles for that.

Anyway, here is a possible solution:

• Create a properties file and put it in your resources folder. Define a placeholder, that gradle can replace. For example file "myapp.properties"

  greetingText=@greeting@
  

• Add the token (the text between the '@'s) to your gradle.properties:

  greeting=Hello world!
  

• Make the build.gradle replace the token with the value from gradle.properties by configuring the processResources task:

  processResources {
      inputs.file file('gradle.properties')
      filter(
              ReplaceTokens, 
              tokens: [
                      greeting: project.ext.greeting
              ]
      )
  

  }

• At runtime load the value from the properties file:

  public String getGreeting() throws IOException {
      try (
          InputStream inputStream = Thread.currentThread().getContextClassLoader().getResource("myapp.properties").openStream();
      ) {
          Properties appProps = new Properties();
          appProps.load(inputStream);
          return appProps.getProperty("greetingText");
      }
  }