When you have 200 concurrent users hitting a single-threaded service, you’ll see the connection pool become a bottleneck, causing java.sql.SQLException: Connection is closed errors. This is because the default connection pool size is not sufficient to handle the load.

## PREREQUISITES To follow this tutorial, you’ll need: * Java 26 or later * Spring Boot 3.0 or later * Maven or Gradle * The following Maven dependency:

 <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> 

For more information on Java and Spring Boot, visit our Java Tutorials Hub. ## UNDERSTANDING PROJECT PANAMA Project Panama is a Java project that aims to improve the performance and scalability of Java applications by providing a foreign function API. The foreign function API allows Java code to call native code, which can improve performance by reducing the overhead of Java’s garbage collection and object creation.

 +---------------+ | Java Code | +---------------+ | | v +---------------+ | Foreign Function| | API | +---------------+ | | v +---------------+ | Native Code | +---------------+ 

The following table compares the different approaches to calling native code from Java:

## STEP-BY-STEP IMPLEMENTATION To implement the foreign function API, follow these steps: ### Step 1: Create a Native Library Create a native library that exports the functions you want to call from Java.

 #include <stdio.h> void hello() { printf("Hello from native code!
"); } 

### Step 2: Create a Java Interface Create a Java interface that defines the functions you want to call from native code.

 public interface NativeLibrary { void hello(); } 

### Step 3: Implement the Foreign Function API Implement the foreign function API by creating a Java class that calls the native code.

 public class NativeLibraryImpl implements NativeLibrary { @Override public void hello() { // Call the native code System.out.println("Calling native code..."); helloNative(); } private native void helloNative(); static { System.loadLibrary("native-library"); } } 

### Step 4: Test the Implementation Test the implementation by calling the Java interface.

 public class Main { public static void main(String[] args) { NativeLibrary nativeLibrary = new NativeLibraryImpl(); nativeLibrary.hello(); } } 

Expected output:

 Calling native code... Hello from native code! 

## COMPLETE WORKING EXAMPLE The following is a complete working example that demonstrates how to use the foreign function API: * `com.example.app` package: + `NativeLibrary.java` interface:

 public interface NativeLibrary { void hello(); } 

+ `NativeLibraryImpl.java` class:

 public class NativeLibraryImpl implements NativeLibrary { @Override public void hello() { // Call the native code System.out.println("Calling native code..."); helloNative(); } private native void helloNative(); static { System.loadLibrary("native-library"); } } 

+ `Main.java` class:

 public class Main { public static void main(String[] args) { NativeLibrary nativeLibrary = new NativeLibraryImpl(); nativeLibrary.hello(); } } 

To test the example, run the following command: “`shell curl -X GET ‘http://localhost:8080/hello’ “` Expected response:

 Hello from native code! 

## COMMON MISTAKES AND HOW TO FIX THEM The following are common mistakes and how to fix them: ### Mistake 1: Not Loading the Native Library If you forget to load the native library, you’ll get a java.lang.UnsatisfiedLinkError exception.

 public class NativeLibraryImpl implements NativeLibrary { @Override public void hello() { // Call the native code System.out.println("Calling native code..."); helloNative(); } private native void helloNative(); // WRONG - causes java.lang.UnsatisfiedLinkError } 

To fix this, add the following code to load the native library:

 static { System.loadLibrary("native-library"); } 

### Mistake 2: Not Implementing the Native Method If you forget to implement the native method, you’ll get a java.lang.UnsatisfiedLinkError exception.

 public class NativeLibraryImpl implements NativeLibrary { @Override public void hello() { // Call the native code System.out.println("Calling native code..."); // WRONG - causes java.lang.UnsatisfiedLinkError } } 

To fix this, add the following code to implement the native method:

 void helloNative() { printf("Hello from native code!
"); } 

## PERFORMANCE AND PRODUCTION TIPS The following are performance and production tips:

Production tip: Use the -Xmx flag to set the maximum heap size to prevent out-of-memory errors.

Production tip: Use the -XX:+UseG1GC flag to enable the G1 garbage collector for better performance.

For more information on Java performance, visit our Java Algorithms tutorial. ## TESTING The following is an example of how to test the foreign function API using JUnit 5:

 public class NativeLibraryTest { @Test public void testHello() { NativeLibrary nativeLibrary = new NativeLibraryImpl(); nativeLibrary.hello(); // Assert that the native code was called assertEquals("Hello from native code!
", System.out.toString()); } } 

For more information on testing, visit our Java Interview Questions tutorial. ## KEY TAKEAWAYS The following are key takeaways: * Use the foreign function API to call native code from Java. * Implement the native method using the native keyword. * Load the native library using the System.loadLibrary method. * Test the implementation using JUnit 5. * Use performance and production tips to improve the performance and scalability of your application. * Visit our SOLID Design Principles in Java tutorial for more information on designing scalable applications. * Visit our Mastering SQL tutorial for more information on database management.