Py4J: Python to Java Bridge

import os
from py4j.java_gateway import JavaGateway, GatewayParameters
import subprocess
import time

# --- Java Gateway Server Setup (for demonstration) ---
# In a real application, the Java Gateway Server would be started separately.
# For this example, we'll try to start a minimal one programmatically.
# This assumes 'py4j<version>.jar' is in the classpath. For simplicity, 
# we'll use a placeholder for py4j.jar path. Users need to replace it.
# Usually, py4j.jar is found in your Python environment's site-packages/py4j/ directory.

# NOTE: Replace '/path/to/py4j<version>.jar' with the actual path to your Py4J JAR file.
# You can find it by running: `python -c "import py4j; import os; print(os.path.join(os.path.dirname(py4j.__file__), 'py4j0.10.9.9.jar'))"`
PY4J_JAR_PATH = os.environ.get('PY4J_JAR_PATH', '/path/to/py4j0.10.9.9.jar') # Update this path!

java_code = """
import py4j.GatewayServer;

public class AdditionApplication {
    public int addition(int first, int second) {
        return first + second;
    }

    public static void main(String[] args) {
        AdditionApplication app = new AdditionApplication();
        GatewayServer server = new GatewayServer(app, 25333);
        server.start();
        System.out.println("Gateway Server Started on port 25333");
    }
}
"""

# Attempt to compile and run the Java code for quickstart demo
# This is a simplification and might require manual setup for complex environments.
# In a production setting, the Java server would be a separate, long-running process.

# Create temporary files for Java code and compiled class
java_file_name = "AdditionApplication.java"
class_file_name = "AdditionApplication.class"

with open(java_file_name, "w") as f:
    f.write(java_code)

try:
    # Compile Java code (requires javac in PATH)
    compile_process = subprocess.run(
        ["javac", "-cp", PY4J_JAR_PATH, java_file_name],
        capture_output=True, text=True
    )
    if compile_process.returncode != 0:
        print("Java compilation failed:", compile_process.stderr)
        print("Please ensure javac is in your PATH and PY4J_JAR_PATH is correct.")
        # Fallback for systems without javac or if compilation fails: manual start instruction
        print("Alternatively, you can manually compile and run the Java server:")
        print(f"1. Save the Java code above as {java_file_name}")
        print(f"2. Compile: javac -cp {PY4J_JAR_PATH} {java_file_name}")
        print(f"3. Run: java -cp {PY4J_JAR_PATH}:. AdditionApplication")
        # If on Windows, use ';' instead of ':' for classpath separator in commands
        raise RuntimeError("Java compilation failed, cannot run quickstart.")

    # Run Java Gateway Server in a separate process
    # Using 'nohup' and '&' for background on *NIX, or 'start' on Windows
    if os.name == 'nt': # Windows
        java_server_command = ["java", "-cp", f".;{PY4J_JAR_PATH}", "AdditionApplication"]
        java_process = subprocess.Popen(java_server_command, creationflags=subprocess.CREATE_NEW_PROCESS_GROUP)
    else: # Unix-like
        java_server_command = ["java", "-cp", f":{PY4J_JAR_PATH}", "AdditionApplication"]
        java_process = subprocess.Popen(java_server_command, preexec_fn=os.setsid)

    print("Starting Java Gateway Server...")
    time.sleep(5) # Give Java server time to start

    # --- Python Client --- 
    gateway = JavaGateway(gateway_parameters=GatewayParameters(port=25333))

    # Access the Java entry point (AdditionApplication instance)
    addition_app = gateway.entry_point

    # Call a Java method
    number1 = 5
    number2 = 3
    result = addition_app.addition(number1, number2)
    print(f"Python calling Java: {number1} + {number2} = {result}")

    # Access JVM directly for standard Java objects
    java_list = gateway.jvm.java.util.ArrayList()
    java_list.add("Hello from Python!")
    print(f"Java list created and modified from Python: {java_list}")

except Exception as e:
    print(f"An error occurred during quickstart: {e}")
finally:
    # Clean up Java process if it was started
    if 'java_process' in locals() and java_process.poll() is None:
        print("Shutting down Java Gateway Server...")
        if os.name == 'nt':
            subprocess.run(["taskkill", "/F", "/T", "/PID", str(java_process.pid)], capture_output=True)
        else:
            os.killpg(os.getpgid(java_process.pid), 15) # Send SIGTERM
        java_process.wait(timeout=5)
    
    # Clean up temporary files
    os.remove(java_file_name) if os.path.exists(java_file_name) else None
    os.remove(class_file_name) if os.path.exists(class_file_name) else None
    # Also remove AdditionApplication$*.class files if they exist
    for f in os.listdir('.'):
        if f.startswith('AdditionApplication$') and f.endswith('.class'):
            os.remove(f)