Chapter 3.  Working with Gradle Build Scripts

A Gradle script is a program. We use a Groovy DSL to express our build logic. Gradle has several useful built-in methods to handle files and directories as we often deal with files and directories in our build logic.

In this chapter, we will discuss how to use Gradle's features to work with files and directories. We will also take a look at how to set properties in a Gradle build and use Gradle's logging framework. Finally, we see will how to use the Gradle Wrapper task to distribute a configurable Gradle with our build scripts.

Working with files

It is very common in a build script that we have to work with files and directories. For example, when we need to copy a file from one directory to another or create a directory to store the output of a task or program.

Locating files

To locate a file or directory relative to the current project, we can use the file() method. This method is actually a method of the Project object that is connected to our build script. In the previous chapter, we discussed how to use an explicit reference to the project variable or simply invoke methods and properties of the Project object implicitly.

The file() method will resolve the location of a file or directory relative to the current project and not the current working directory. This is very useful as we can run a build script from a different directory than the location of the actual build script. File or directory references that are returned by the file() method are then resolved, relative to the project directory.

We can pass any...

Project properties

In a Gradle build file, we can access several properties that are defined by Gradle, but we can also create our own properties. We can set the value of our custom properties directly in the build script and we can also do this by passing values via the command line.

The default properties that we can access in a Gradle build are displayed in the following table:

Using logging

In Chapter 1 , Starting with Gradle, we discussed several command-line options that we can use to show either more or fewer log messages when we run a Gradle build. These messages were from the Gradle internal tasks and classes. We used a println method in our Gradle build scripts to see some output, but we can also use Gradle's logging mechanisms to have a more customizable way to define logging messages.

Gradle supports several logging levels that we can use for our own messages. The level of our messages is important as we can use the command-line options to filter the messages for log levels.

The following table shows the log levels that are supported by Gradle:

Name	Type	Default value
project	Project	The project instance.
name	String	The name of the project directory. The name is read-only.
path	String	The absolute path of the project.
description	String	The description of the project.
projectDir	File	The directory containing the build script. The value is read-only.
buildDir	File	The directory with the build name in the directory, containing the build script.
rootDir	File	The directory of the project at the root of a project structure.
group	Object	Not specified.
version	Object	Not specified.
ant	AntBuilder...

Level	Used for
DEBUG	Debug messages
INFO	Information messages
LIFECYCLE	Progress information messages
WARNING	Warning messages
QUIET	Import information messages
ERROR	Error messages

Every Gradle build file and task has a logger object. The logger object is an instance of a Gradle-specific...

Using the Gradle Wrapper

Normally, if we want to run a Gradle build, we must have Gradle installed on our computer. Also, if we distribute our project to others and they want to build the project, they must have Gradle installed on their computers. The Gradle Wrapper can be used to allow others to build our project even if they don't have Gradle installed on their computers.

The wrapper is a batch script on the Microsoft Windows operating systems or shell script on other operating systems that will download Gradle and run the build using the downloaded Gradle.

By using the wrapper, we can make sure that the correct Gradle version for the project is used. We can define the Gradle version, and if we run the build via the wrapper script file, the version of Gradle that we defined is used.

Creating wrapper scripts

To create the Gradle Wrapper batch and shell scripts, we can invoke the built-in wrapper task. This task is already available if we have installed Gradle on our computer. Let's invoke...

Summary

In this chapter, we discussed the support that Gradle gives when working with files. We saw how to create a file or directory and a collection of files and directories. A file tree represents a hierarchical set of files.

We can add logging messages to our project and tasks and see the output when we run a Gradle build. We discussed how to use different log levels to influence how much information is shown in the output. We also used LoggingManager to capture the standard output and error messages and redirect them to custom log levels.

We discussed how to use the Gradle Wrapper to allow users to build our projects even if they don't have Gradle installed. We discussed how to customize the Wrapper to download a specific version of Gradle and use it to run our build.

In the next chapter, we will create a Java project and use the Java plugin to add a set of default tasks that we can use to compile, test, and package our Java code.

The rest of the chapter is locked

Using logging

In Chapter 1 , Starting with Gradle, we discussed several command-line options that we can use to show either more or fewer log messages when we run a Gradle build. These messages were from the Gradle internal tasks and classes. We used a println method in our Gradle build scripts to see some output, but we can also use Gradle's logging mechanisms to have a more customizable way to define logging messages.

Gradle supports several logging levels that we can use for our own messages. The level of our messages is important as we can use the command-line options to filter the messages for log levels.

The following table shows the log levels that are supported by Gradle:

Using the Gradle Wrapper

Normally, if we want to run a Gradle build, we must have Gradle installed on our computer. Also, if we distribute our project to others and they want to build the project, they must have Gradle installed on their computers. The Gradle Wrapper can be used to allow others to build our project even if they don't have Gradle installed on their computers.

The wrapper is a batch script on the Microsoft Windows operating systems or shell script on other operating systems that will download Gradle and run the build using the downloaded Gradle.

By using the wrapper, we can make sure that the correct Gradle version for the project is used. We can define the Gradle version, and if we run the build via the wrapper script file, the version of Gradle that we defined is used.

Creating wrapper scripts

To create the Gradle Wrapper batch and shell scripts, we can invoke the built-in wrapper task. This task is already available if we have installed Gradle on our computer. Let's invoke...

Summary

In this chapter, we discussed the support that Gradle gives when working with files. We saw how to create a file or directory and a collection of files and directories. A file tree represents a hierarchical set of files.

We can add logging messages to our project and tasks and see the output when we run a Gradle build. We discussed how to use different log levels to influence how much information is shown in the output. We also used LoggingManager to capture the standard output and error messages and redirect them to custom log levels.

We discussed how to use the Gradle Wrapper to allow users to build our projects even if they don't have Gradle installed. We discussed how to customize the Wrapper to download a specific version of Gradle and use it to run our build.

In the next chapter, we will create a Java project and use the Java plugin to add a set of default tasks that we can use to compile, test, and package our Java code.