Why Manual JAR Deployment Is Outdated and How Dynamic Hot‑Deploy Makes It Easy

Define a Simple Interface

Example of a Calculator interface with calculate and add methods.

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

Simple Implementation

Two implementations: annotation‑based (managed by Spring) and reflection‑based.

@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

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

Reflection‑Based Hot Deployment

Upload JAR path, load with URLClassLoader, instantiate class, invoke add.

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);
}

Annotation‑Based Hot Deployment

Load JAR, scan classes, register beans whose classes carry Spring stereotypes.

public static void hotDeployWithSpring() throws Exception {
    Set<String> 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());
        }
    }
}

Removing Beans When JAR Is Deleted

Iterate classes, if Spring bean, remove its definition from the same BeanFactory.

public static void delete() throws Exception {
    Set<String> 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));
        }
    }
}

DeployUtils Helper Methods

Methods to read all class names from a JAR, check for Spring annotations, and convert class names to bean IDs.

public static Set<String> readJarFile(String jarAddress) throws IOException {
    Set<String> classNameSet = new HashSet<>();
    JarFile jarFile = new JarFile(jarAddress);
    Enumeration<JarEntry> entries = jarFile.entries();
    while (entries.hasMoreElements()) {
        JarEntry jarEntry = entries.nextElement();
        String name = jarEntry.getName();
        if (name.endsWith(".class")) {
            String className = name.replace(".class", "").replaceAll("/", ".");
            classNameSet.add(className);
        }
    }
    return classNameSet;
}

public static boolean isSpringBeanClass(Class<?> cla) {
    if (cla == null || cla.isInterface() || Modifier.isAbstract(cla.getModifiers())) {
        return false;
    }
    return cla.getAnnotation(Component.class) != null ||
           cla.getAnnotation(Repository.class) != null ||
           cla.getAnnotation(Service.class) != null;
}

public static String transformName(String className) {
    String tmpstr = className.substring(className.lastIndexOf(".") + 1);
    return tmpstr.substring(0, 1).toLowerCase() + tmpstr.substring(1);
}

Test Loop

Continuously attempts hot deployment; if the JAR is not found, catches the exception, waits ten seconds, then retries.

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);
    }
}