[BAEL-7257] Monkey-Patching in Java (#15700)

2024-01-22 20:09:24 +02:00
parent 7ff914a1b3
commit f6806580ae
15 changed files with 295 additions and 0 deletions
@@ -0,0 +1,12 @@
+package com.baeldung.monkey.patching;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class Application {
+
+    public static void main(String[] args) {
+        SpringApplication.run(Application.class, args);
+    }
+}
@@ -0,0 +1,15 @@
+package com.baeldung.monkey.patching.aop;
+
+import com.baeldung.monkey.patching.converter.MoneyConverter;
+import com.baeldung.monkey.patching.converter.MoneyConverterImpl;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class BeanConfiguration {
+
+    @Bean
+    public MoneyConverter moneyConverter() {
+        return new MoneyConverterImpl();
+    }
+}
@@ -0,0 +1,22 @@
+package com.baeldung.monkey.patching.aop;
+
+import org.aspectj.lang.JoinPoint;
+import org.aspectj.lang.annotation.After;
+import org.aspectj.lang.annotation.Aspect;
+import org.aspectj.lang.annotation.Before;
+import org.springframework.stereotype.Component;
+
+@Aspect
+@Component
+public class LoggingAspect {
+
+    @Before("execution(* com.baeldung.monkey.patching.converter.MoneyConverter.convertEURtoUSD(..))")
+    public void beforeConvertEURtoUSD(JoinPoint joinPoint) {
+        System.out.println("Before method: " + joinPoint.getSignature().getName());
+    }
+
+    @After("execution(* com.baeldung.monkey.patching.converter.MoneyConverter.convertEURtoUSD(..))")
+    public void afterConvertEURtoUSD(JoinPoint joinPoint) {
+        System.out.println("After method: " + joinPoint.getSignature().getName());
+    }
+}
@@ -0,0 +1,5 @@
+package com.baeldung.monkey.patching.converter;
+
+public interface MoneyConverter {
+    double convertEURtoUSD(double amount);
+}
@@ -0,0 +1,15 @@
+package com.baeldung.monkey.patching.converter;
+
+public class MoneyConverterImpl implements MoneyConverter {
+
+    private final double conversionRate;
+
+    public MoneyConverterImpl() {
+        this.conversionRate = 1.10;
+    }
+
+    @Override
+    public double convertEURtoUSD(double amount) {
+        return amount * conversionRate;
+    }
+}
@@ -0,0 +1,21 @@
+package com.baeldung.monkey.patching.decorator;
+
+import com.baeldung.monkey.patching.converter.MoneyConverter;
+
+public class MoneyConverterDecorator implements MoneyConverter {
+
+    private final MoneyConverter moneyConverter;
+
+    public MoneyConverterDecorator(MoneyConverter moneyConverter) {
+        this.moneyConverter = moneyConverter;
+    }
+
+    @Override
+    public double convertEURtoUSD(double amount) {
+
+        System.out.println("Before method: convertEURtoUSD");
+        double result = moneyConverter.convertEURtoUSD(amount);
+        System.out.println("After method: convertEURtoUSD");
+        return result;
+    }
+}
@@ -0,0 +1,21 @@
+package com.baeldung.monkey.patching.proxy;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+
+public class LoggingInvocationHandler implements InvocationHandler {
+
+    private final Object target;
+
+    public LoggingInvocationHandler(Object target) {
+        this.target = target;
+    }
+
+    @Override
+    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+        System.out.println("Before method: " + method.getName());
+        Object result = method.invoke(target, args);
+        System.out.println("After method: " + method.getName());
+        return result;
+    }
+}
@@ -0,0 +1,35 @@
+package com.baeldung.monkey.patching.aop;
+
+import com.baeldung.monkey.patching.converter.MoneyConverter;
+import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+
+import static org.junit.Assert.assertTrue;
+
+@SpringBootTest
+@RunWith(SpringRunner.class)
+public class LoggingAspectIntegrationTest {
+
+    @Autowired
+    private MoneyConverter moneyConverter;
+
+    @Test
+    public void whenMethodCalled_thenSurroundedByLogs() {
+        ByteArrayOutputStream logOutputStream = new ByteArrayOutputStream();
+        System.setOut(new PrintStream(logOutputStream));
+
+        double result = moneyConverter.convertEURtoUSD(10);
+
+        Assertions.assertEquals(11, result);
+        String logOutput = logOutputStream.toString();
+        assertTrue(logOutput.contains("Before method: convertEURtoUSD"));
+        assertTrue(logOutput.contains("After method: convertEURtoUSD"));
+    }
+}
@@ -0,0 +1,17 @@
+package com.baeldung.monkey.patching.converter;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class MoneyConverterUnitTest {
+
+    @Test
+    void whenMoneyConverter_thenResultIsCorrect() {
+        MoneyConverterImpl moneyConverter = new MoneyConverterImpl();
+
+        double result = moneyConverter.convertEURtoUSD(10);
+
+        assertEquals(11, result);
+    }
+}
@@ -0,0 +1,28 @@
+package com.baeldung.monkey.patching.decorator;
+
+import com.baeldung.monkey.patching.converter.MoneyConverter;
+import com.baeldung.monkey.patching.converter.MoneyConverterImpl;
+import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+
+import static org.junit.Assert.assertTrue;
+
+public class MoneyConverterDecoratorUnitTest {
+
+    @Test
+    public void whenMethodCalled_thenSurroundedByLogs() {
+        ByteArrayOutputStream logOutputStream = new ByteArrayOutputStream();
+        System.setOut(new PrintStream(logOutputStream));
+        MoneyConverter moneyConverter = new MoneyConverterDecorator(new MoneyConverterImpl());
+
+        double result = moneyConverter.convertEURtoUSD(10);
+
+        Assertions.assertEquals(11, result);
+        String logOutput = logOutputStream.toString();
+        assertTrue(logOutput.contains("Before method: convertEURtoUSD"));
+        assertTrue(logOutput.contains("After method: convertEURtoUSD"));
+    }
+}
@@ -0,0 +1,34 @@
+package com.baeldung.monkey.patching.proxy;
+
+import com.baeldung.monkey.patching.converter.MoneyConverter;
+import com.baeldung.monkey.patching.converter.MoneyConverterImpl;
+import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.lang.reflect.Proxy;
+
+import static org.junit.Assert.assertTrue;
+
+public class LoggingInvocationHandlerUnitTest {
+
+    @Test
+    public void whenMethodCalled_thenSurroundedByLogs() {
+        ByteArrayOutputStream logOutputStream = new ByteArrayOutputStream();
+        System.setOut(new PrintStream(logOutputStream));
+        MoneyConverter moneyConverter = new MoneyConverterImpl();
+        MoneyConverter proxy = (MoneyConverter) Proxy.newProxyInstance(
+                MoneyConverter.class.getClassLoader(),
+                new Class[]{MoneyConverter.class},
+                new LoggingInvocationHandler(moneyConverter)
+        );
+
+        double result = proxy.convertEURtoUSD(10);
+
+        Assertions.assertEquals(11, result);
+        String logOutput = logOutputStream.toString();
+        assertTrue(logOutput.contains("Before method: convertEURtoUSD"));
+        assertTrue(logOutput.contains("After method: convertEURtoUSD"));
+    }
+}
@@ -0,0 +1,24 @@
+package com.baeldung.monkey.patching.reflection;
+
+import com.baeldung.monkey.patching.converter.MoneyConverter;
+import com.baeldung.monkey.patching.converter.MoneyConverterImpl;
+import org.junit.Test;
+
+import java.lang.reflect.Field;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ReflectionUnitTest {
+
+@Test
+public void givenPrivateField_whenUsingReflection_thenBehaviorCanBeChanged() throws IllegalAccessException, NoSuchFieldException {
+    MoneyConverter moneyConvertor = new MoneyConverterImpl();
+
+    Field conversionRate = MoneyConverterImpl.class.getDeclaredField("conversionRate");
+    conversionRate.setAccessible(true);
+    conversionRate.set(moneyConvertor, 1.2);
+    double result = moneyConvertor.convertEURtoUSD(10);
+
+    assertEquals(12, result);
+}
+}