Apache Thrift - Generating Code

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Generating Code in Apache Thrift

Generating code from Apache Thrift IDL files is an important step in creating a cross-language service.

The Thrift compiler (thrift) takes the IDL file and produces source code in the target programming languages, which can then be used to implement and interact with the defined services.

This tutorial provides a detailed guide on how to generate code using Apache Thrift, including setting up the environment, running the compiler, and handling generated code.

Setting Up the Environment

Before generating code, ensure that you have the Thrift compiler installed and that your development environment is configured properly.

  • Install the Thrift Compiler: In "Linux/macOS", follow the installation instructions for your operating system, such as using "apt" for Ubuntu or "brew" for macOS. In "Windows", download and install pre-compiled binaries or build from source using CMake.
  • Verify Installation: Confirm that the "thrift" command is available in your system's PATH.
thrift --version
  • Prepare Your IDL File: Ensure you have a Thrift IDL file (e.g., service.thrift) that defines the data types and services you want to use.

    • Running the Thrift Compiler

    The Thrift compiler is used to generate source code in various programming languages from the IDL file. Here is how to run the compiler :

    • Basic Command Structure: The basic command to generate code is given below. Replace "<language>" with the target programming language and "<path-to-idl-file>" with the path to your Thrift IDL file −
    thrift --gen <language> <path-to-idl-file>
  • Example for Java: To generate Java code from "service.thrift", execute the following command, this will create a directory named "gen-java" with the generated Java source files −
    • thrift --gen java service.thrift

  • Example for Python: To generate Python code from "service.thrift", execute the following command, this will create a directory named "gen-py" with the generated Python source files −
    • thrift --gen py service.thrift
  • Handling Multiple Languages: You can generate code for multiple languages in a single command −
    • thrift --gen java --gen py service.thrift

    Understanding Generated Code

    The generated code will include various files depending on the target language and the contents of the IDL file. Here is an overview of what you can expect :

    Java Generated Code

    When you generate Java code from a Thrift IDL file, the output consists of several key components that are organized to facilitate the implementation and use of the defined services. Here is a detailed explanation of each component and the directory structure −

    • Data Types: Java classes for structs, enums, and exceptions.
    • Service Interfaces: Java interfaces for the services defined in the IDL.
    • Client and Server Stubs: Classes for client and server-side communication.

    Following is the example directory structure −

    gen-java/
 example/
    Color.java
    Person.java
    Greeter.java
 TBinaryProtocol.java

    Where,

    • gen-java/: The root directory where all generated Java code is stored.
    • example/: A subdirectory containing the generated Java files organized by the namespace defined in the IDL file.
    • Color.java: Contains the Java enum class for the Color enum defined in the IDL.
    • Person.java: Contains the Java class for the Person struct.
    • Greeter.java: Contains the Java interface for the Greeter service.
    • TBinaryProtocol.java: A utility class for handling Thrifts binary protocol, which is used for encoding and decoding data in Thrift.

    Python Generated Code

    When you generate Python code from a Thrift IDL file, the output includes various Python modules that correspond to the data types, service interfaces, and communication stubs defined in the IDL.

    These modules are structured in a way that supports easy integration into your Python projects. Here is a detailed explanation of each component and the directory structure :

    • Data Types: Python classes for structs and enums.
    • Service Interfaces: Python classes for service methods.
    • Client and Server Stubs: Python modules for client and server-side communication.

    The following generated Python code is organized in a directory structure that mirrors the namespace defined in the IDL file :

    gen-py/
 example/
    __init__.py
    color.py
    person.py
    greeter.py
 __init__.py
    • gen-py/: The root directory where all generated Python code is stored.
    • example/: A subdirectory corresponding to the namespace defined in the IDL file. This directory contains the Python modules generated from the IDL.
    • \_\_init\_\_.py: An empty file that makes the example directory a Python package, allowing you to import the generated modules as a package.
    • color.py: Contains the Color enum class, which defines the enumerated values for the Color type.
    • person.py: Contains the Person class, which defines the structure and attributes of the Person struct.
    • greeter.py: Contains the Greeter service class, including methods like greet and getAge.
    • \_\_init\_\_.py: Another \_\_init\_\_.py file at the root level, which may be used if the entire gen-py directory is treated as a Python package.

    Integrating Generated Code

    Once the code is generated, integrate it into your project as follows :

    For Java Integration :

    • Include the Generated Code: Add the "gen-java" directory to your Java projects build path.
    • Compile and Use: Compile the generated code along with your project code and use the generated classes and interfaces to implement and interact with the services.

    For Python Integration :

    • Include the Generated Code: Add the "gen-py" directory to your Python path.
    • Import and Use: Import the generated modules in your Python code and use the classes and methods to implement and interact with the services.

    Compiling and Running Code

    Once you have generated the code from your Thrift IDL file, the next step is to compile (if necessary) and run your application.

    Java Compilation and Execution

    In Java, after generating the code, you need to compile the generated classes along with any additional Java code youve written. Here is how you can do it :

    Compile the Java Code:

    • Use the "javac" command to compile the generated Java files and any custom Java code you have written.
    • Include the path to the generated code and any required Thrift runtime libraries in the classpath.
    • For example, if you have a "src" directory containing your Java files and a "gen-java" directory containing the generated code, you would compile it like this −
    javac -d bin -cp path/to/thrift/lib/* src/**/*.java gen-java/**/*.java
  • "-d bin" specifies the output directory for compiled classes.
  • "-cp" specifies the classpath, including the Thrift runtime library and any other dependencies.

    • Run the Java Application:

    • After compiling, you can run your Java application using the "java" command.
    • Make sure to include the compiled classes and necessary libraries in the classpath.
    • For example, if your main class is "com.example.Main", you would run it like this −
    java -cp bin:path/to/thrift/lib/* com.example.Main
  • This command runs your Java application, allowing it to start the Thrift server or client depending on your implementation.

    • Python Execution

    Python does not require a compilation step, as it is an interpreted language. Once the Thrift code is generated, you can directly execute your Python scripts. Here is how you can do it :

    Running the Python Code:

    • Ensure the generated code is accessible by your Python script, typically by adding the "gen-py" directory to the Python path.
    • You can do this by either running the script from the root directory where "gen-py" is located or modifying the "PYTHONPATH" environment variable.
    • For example, if your script is named "client.py" and located in the same directory as "gen-py", you would run it like this −
    python client.py
  • This command will execute your script, which should include imports from the generated code and interact with the Thrift service (either as a client or a server).

    • Python Path Setup:

    • If you need to manually set the Python path, you can do so by exporting the "PYTHONPATH" environment variable −
    export PYTHONPATH=$PYTHONPATH:/path/to/gen-py
  • Alternatively, in your Python script, you can programmatically add the path −
    • import sys
sys.path.append('/path/to/gen-py')

    Verifying the Execution

    Yo can verify the execution for Java as shown below :

    • Check the console output to verify that your Java application is running as expected, whether it's starting a Thrift server or making client requests.
    • Handle any exceptions or errors that arise, often related to networking issues or incorrect classpath settings.

    Verify the execution for Python as shown below :

    • Check the console output to confirm that your Python script is executing the Thrift service operations as expected.
    • Ensure that all necessary modules are imported correctly and that the Thrift service is reachable.
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