Dynamic Proxy (#1702)

core-java/src/main/java/com/baeldung/dynamicproxy/DynamicInvocationHandler.java

@@ -0,0 +1,19 @@
+package com.baeldung.dynamicproxy;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+
+public class DynamicInvocationHandler implements InvocationHandler {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(DynamicInvocationHandler.class);
+
+    @Override
+    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+        LOGGER.info("Invoked method: {}", method.getName());
+
+        return 42;
+    }
+}

core-java/src/main/java/com/baeldung/dynamicproxy/TimingDynamicInvocationHandler.java

@@ -0,0 +1,36 @@
+package com.baeldung.dynamicproxy;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class TimingDynamicInvocationHandler implements InvocationHandler {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(TimingDynamicInvocationHandler.class);
+    private final Map<String, Method> methods = new HashMap<>();
+
+    private Object target;
+
+    public TimingDynamicInvocationHandler(Object target) {
+        this.target = target;
+
+        for(Method method: target.getClass().getDeclaredMethods()) {
+            this.methods.put(method.getName(), method);
+        }
+    }
+
+    @Override
+    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+        long start = System.nanoTime();
+        Object result = methods.get(method.getName()).invoke(target, args);
+        long elapsed = System.nanoTime() - start;
+
+        LOGGER.info("Executing {} finished in {} ns", method.getName(), elapsed);
+
+        return result;
+    }
+}

core-java/src/test/java/com/baeldung/dynamicproxy/DynamicProxyTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.dynamicproxy;
+
+import org.junit.Test;
+
+import java.lang.reflect.Proxy;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+import static org.testng.Assert.fail;
+
+public class DynamicProxyTest {
+
+    @Test
+    public void givenDynamicProxy_thenPutWorks() {
+        Map proxyInstance = (Map) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { Map.class }, new DynamicInvocationHandler());
+
+        proxyInstance.put("hello", "world");
+    }
+
+    @Test
+    public void givenInlineDynamicProxy_thenGetWorksOtherMethodsDoNot() {
+        Map proxyInstance = (Map) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { Map.class }, (proxy, method, methodArgs) -> {
+
+            if (method.getName().equals("get")) {
+                return 42;
+            } else {
+                throw new UnsupportedOperationException("Unsupported method: " + method.getName());
+            }
+        });
+
+        int result = (int) proxyInstance.get("hello");
+
+        assertEquals(42, result);
+
+        try {
+            proxyInstance.put("hello", "world");
+            fail();
+        } catch(UnsupportedOperationException e) {
+            // expected
+        }
+    }
+
+    @Test
+    public void givenTimingDynamicProxy_thenMethodInvokationsProduceTiming() {
+        Map mapProxyInstance = (Map) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { Map.class }, new TimingDynamicInvocationHandler(new HashMap<>()));
+
+        mapProxyInstance.put("hello", "world");
+        assertEquals("world", mapProxyInstance.get("hello"));
+
+        CharSequence csProxyInstance = (CharSequence) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { CharSequence.class }, new TimingDynamicInvocationHandler("Hello World"));
+
+        assertEquals('l', csProxyInstance.charAt(2));
+        assertEquals(11, csProxyInstance.length());
+    }
+
+}