Hot Deployment of Custom Interface Implementations in Java Using Reflection and Spring

Define Simple Interface

First, a Calculator interface with calculate and add methods is defined.

public interface Calculator {
    int calculate(int a, int b);
    int add(int a, int b);
}

Implementation Class

The implementation provides two ways: annotation‑based ( calculate ) and reflection‑based ( add ). It injects CalculatorCore to demonstrate bean dependency construction.

@Service
public class CalculatorImpl implements Calculator {
    @Autowired
    CalculatorCore calculatorCore;

    // annotation way
    @Override
    public int calculate(int a, int b) {
        int c = calculatorCore.add(a, b);
        return c;
    }

    // reflection way
    @Override
    public int add(int a, int b) {
        return new CalculatorCore().add(a, b);
    }
}

CalculatorCore

Simple component providing the add operation.

@Service
public class CalculatorCore {
    public int add(int a, int b) {
        return a + b;
    }
}

Reflection‑Based Hot Deployment

Upload a JAR to a predefined directory, load it with URLClassLoader , obtain the implementation class by name, instantiate it via reflection, and invoke the method.

private static String jarAddress = "E:/zzq/IDEA_WS/CalculatorTest/lib/Calculator.jar";
private static String jarPath = "file:/" + jarAddress;

public static void hotDeployWithReflect() throws Exception {
    URLClassLoader urlClassLoader = new URLClassLoader(
        new URL[]{new URL(jarPath)},
        Thread.currentThread().getContextClassLoader());
    Class clazz = urlClassLoader.loadClass("com.nci.cetc15.calculator.impl.CalculatorImpl");
    Calculator calculator = (Calculator) clazz.newInstance();
    int result = calculator.add(1, 2);
    System.out.println(result);
}

Spring‑Based Hot Deployment

If the uploaded JAR contains Spring components, scan all classes, register beans whose classes carry @Component , @Service , or @Repository annotations into the current Spring container.

public static void hotDeployWithSpring() throws Exception {
    Set
classNameSet = DeployUtils.readJarFile(jarAddress);
    URLClassLoader urlClassLoader = new URLClassLoader(
        new URL[]{new URL(jarPath)},
        Thread.currentThread().getContextClassLoader());
    for (String className : classNameSet) {
        Class clazz = urlClassLoader.loadClass(className);
        if (DeployUtils.isSpringBeanClass(clazz)) {
            BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition(clazz);
            defaultListableBeanFactory.registerBeanDefinition(
                DeployUtils.transformName(className), beanDefinitionBuilder.getBeanDefinition());
        }
    }
}

Utility Methods

DeployUtils provides methods to read all class entries from a JAR, determine whether a class is a Spring bean, and transform class names to bean IDs.

public static Set
readJarFile(String jarAddress) throws IOException { /* ... */ }
public static boolean isSpringBeanClass(Class
cla) { /* ... */ }
public static String transformName(String className) { /* ... */ }

Bean Removal on JAR Deletion

When a JAR is removed, the previously registered beans are also deregistered from the Spring container.

public static void delete() throws Exception {
    Set
classNameSet = DeployUtils.readJarFile(jarAddress);
    URLClassLoader urlClassLoader = new URLClassLoader(
        new URL[]{new URL(jarPath)},
        Thread.currentThread().getContextClassLoader());
    for (String className : classNameSet) {
        Class clazz = urlClassLoader.loadClass(className);
        if (DeployUtils.isSpringBeanClass(clazz)) {
            defaultListableBeanFactory.removeBeanDefinition(DeployUtils.transformName(className));
        }
    }
}

Test Harness

A simple loop repeatedly attempts hot deployment, sleeping when the JAR is not yet present.

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
DefaultListableBeanFactory defaultListableBeanFactory = (DefaultListableBeanFactory) applicationContext.getAutowireCapableBeanFactory();
while (true) {
    try {
        hotDeployWithReflect();
        // hotDeployWithSpring();
        // delete();
    } catch (Exception e) {
        e.printStackTrace();
        Thread.sleep(1000 * 10);
    }
}