Merge pull request #8125 from eugenp/revert-8119-BAEL-3275-2

Revert "BAEL-3275: Using blocking queue for pub-sub"

core-java-modules/core-java-jvm/README.md

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+## Core Java JVM Cookbooks and Examples
+
+This module contains articles about working with the Java Virtual Machine (JVM).
+
+### Relevant Articles: 
+
+- [Method Inlining in the JVM](https://www.baeldung.com/jvm-method-inlining)
+- [JVM Log Forging](https://www.baeldung.com/jvm-log-forging)
+- [Guide to Java Instrumentation](https://www.baeldung.com/java-instrumentation)
+- [Class Loaders in Java](https://www.baeldung.com/java-classloaders)
+- [A Guide to System.exit()](https://www.baeldung.com/java-system-exit)
+- [Guide to System.gc()](https://www.baeldung.com/java-system-gc)

core-java-modules/core-java-jvm/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-jvm</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>core-java-jvm</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../../</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.javassist</groupId>
+            <artifactId>javassist</artifactId>
+            <version>${javaassist.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.owasp.esapi</groupId>
+            <artifactId>esapi</artifactId>
+            <version>${esapi.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.sun</groupId>
+            <artifactId>tools</artifactId>
+            <version>${sun.tools.version}</version>
+            <scope>system</scope>
+            <systemPath>${java.home}/../lib/tools.jar</systemPath>
+        </dependency>
+
+    </dependencies>
+
+    <properties>
+        <assertj.version>3.6.1</assertj.version>
+        <!-- instrumentation -->
+        <javaassist.version>3.21.0-GA</javaassist.version>
+        <esapi.version>2.1.0.1</esapi.version>
+        <sun.tools.version>1.8.0</sun.tools.version>
+    </properties>
+</project>

core-java-modules/core-java-jvm/src/main/java/com/baeldung/classloader/CustomClassLoader.java

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+package com.baeldung.classloader;
+
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+
+public class CustomClassLoader extends ClassLoader {
+
+    @Override
+    public Class findClass(String name) throws ClassNotFoundException {
+        byte[] b = loadClassFromFile(name);
+        return defineClass(name, b, 0, b.length);
+    }
+
+    private byte[] loadClassFromFile(String fileName)  {
+        InputStream inputStream = getClass().getClassLoader().getResourceAsStream(
+                fileName.replace('.', File.separatorChar) + ".class");
+        byte[] buffer;
+        ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
+        int nextValue = 0;
+        try {
+            while ( (nextValue = inputStream.read()) != -1 ) {
+                byteStream.write(nextValue);
+            }
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        buffer = byteStream.toByteArray();
+        return buffer;
+    }
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/classloader/PrintClassLoader.java

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+package com.baeldung.classloader;
+
+import com.sun.javafx.util.Logging;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLConnection;
+import java.util.ArrayList;
+
+public class PrintClassLoader {
+
+    public void printClassLoaders() throws ClassNotFoundException {
+
+        System.out.println("Classloader of this class:" + PrintClassLoader.class.getClassLoader());
+        System.out.println("Classloader of Logging:" + Logging.class.getClassLoader());
+        System.out.println("Classloader of ArrayList:" + ArrayList.class.getClassLoader());
+
+    }
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/inlining/ConsecutiveNumbersSum.java

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+package com.baeldung.inlining;
+
+public class ConsecutiveNumbersSum {
+
+    private long totalSum;
+    private int totalNumbers;
+
+    public ConsecutiveNumbersSum(int totalNumbers) {
+        this.totalNumbers = totalNumbers;
+    }
+
+    public long getTotalSum() {
+        totalSum = 0;
+        for (int i = 1; i <= totalNumbers; i++) {
+            totalSum += i;
+        }
+        return totalSum;
+    }
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/inlining/InliningExample.java

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+package com.baeldung.inlining;
+
+public class InliningExample {
+
+    public static final int NUMBERS_OF_ITERATIONS = 15000;
+
+    public static void main(String[] args) {
+        for (int i = 1; i < NUMBERS_OF_ITERATIONS; i++) {
+            calculateSum(i);
+        }
+    }
+
+    private static long calculateSum(int n) {
+        return new ConsecutiveNumbersSum(n).getTotalSum();
+    }
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/instrumentation/agent/AtmTransformer.java

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+package com.baeldung.instrumentation.agent;
+
+import javassist.CannotCompileException;
+import javassist.ClassPool;
+import javassist.CtClass;
+import javassist.CtMethod;
+import javassist.NotFoundException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.security.ProtectionDomain;
+
+public class AtmTransformer implements ClassFileTransformer {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(AtmTransformer.class);
+
+    private static final String WITHDRAW_MONEY_METHOD = "withdrawMoney";
+
+    /** The internal form class name of the class to transform */
+    private String targetClassName;
+    /** The class loader of the class we want to transform */
+    private ClassLoader targetClassLoader;
+
+    public AtmTransformer(String targetClassName, ClassLoader targetClassLoader) {
+        this.targetClassName = targetClassName;
+        this.targetClassLoader = targetClassLoader;
+    }
+
+    @Override
+    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
+            ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
+        byte[] byteCode = classfileBuffer;
+
+        String finalTargetClassName = this.targetClassName.replaceAll("\\.", "/"); //replace . with /
+        if (!className.equals(finalTargetClassName)) {
+            return byteCode;
+        }
+
+        if (className.equals(finalTargetClassName) && loader.equals(targetClassLoader)) {
+            LOGGER.info("[Agent] Transforming class MyAtm");
+            try {
+                ClassPool cp = ClassPool.getDefault();
+                CtClass cc = cp.get(targetClassName);
+                CtMethod m = cc.getDeclaredMethod(WITHDRAW_MONEY_METHOD);
+                m.addLocalVariable("startTime", CtClass.longType);
+                m.insertBefore("startTime = System.currentTimeMillis();");
+
+                StringBuilder endBlock = new StringBuilder();
+
+                m.addLocalVariable("endTime", CtClass.longType);
+                m.addLocalVariable("opTime", CtClass.longType);
+                endBlock.append("endTime = System.currentTimeMillis();");
+                endBlock.append("opTime = (endTime-startTime)/1000;");
+
+                endBlock.append("LOGGER.info(\"[Application] Withdrawal operation completed in:\" + opTime + \" seconds!\");");
+
+                m.insertAfter(endBlock.toString());
+
+                byteCode = cc.toBytecode();
+                cc.detach();
+            } catch (NotFoundException | CannotCompileException | IOException e) {
+                LOGGER.error("Exception", e);
+            }
+        }
+        return byteCode;
+    }
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/instrumentation/agent/MyInstrumentationAgent.java

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+package com.baeldung.instrumentation.agent;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.lang.instrument.Instrumentation;
+
+public class MyInstrumentationAgent {
+    private static Logger LOGGER = LoggerFactory.getLogger(MyInstrumentationAgent.class);
+
+    public static void premain(String agentArgs, Instrumentation inst) {
+        LOGGER.info("[Agent] In premain method");
+
+        String className = "com.baeldung.instrumentation.application.MyAtm";
+        transformClass(className,inst);
+    }
+
+    public static void agentmain(String agentArgs, Instrumentation inst) {
+        LOGGER.info("[Agent] In agentmain method");
+
+        String className = "com.baeldung.instrumentation.application.MyAtm";
+        transformClass(className,inst);
+    }
+
+    private static void transformClass(String className, Instrumentation instrumentation) {
+        Class<?> targetCls = null;
+        ClassLoader targetClassLoader = null;
+        // see if we can get the class using forName
+        try {
+            targetCls = Class.forName(className);
+            targetClassLoader = targetCls.getClassLoader();
+            transform(targetCls, targetClassLoader, instrumentation);
+            return;
+        } catch (Exception ex) {
+            LOGGER.error("Class [{}] not found with Class.forName");
+        }
+        // otherwise iterate all loaded classes and find what we want
+        for(Class<?> clazz: instrumentation.getAllLoadedClasses()) {
+            if(clazz.getName().equals(className)) {
+                targetCls = clazz;
+                targetClassLoader = targetCls.getClassLoader();
+                transform(targetCls, targetClassLoader, instrumentation);
+                return;
+            }
+        }
+        throw new RuntimeException("Failed to find class [" + className + "]");
+    }
+
+    private static void transform(Class<?> clazz, ClassLoader classLoader, Instrumentation instrumentation) {
+        AtmTransformer dt = new AtmTransformer(clazz.getName(), classLoader);
+        instrumentation.addTransformer(dt, true);
+        try {
+            instrumentation.retransformClasses(clazz);
+        } catch (Exception ex) {
+            throw new RuntimeException("Transform failed for class: [" + clazz.getName() + "]", ex);
+        }
+    }
+
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/instrumentation/application/AgentLoader.java

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+package com.baeldung.instrumentation.application;
+
+import com.sun.tools.attach.VirtualMachine;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
+import java.util.Optional;
+
+/**
+ * Created by adi on 6/10/18.
+ */
+public class AgentLoader {
+    private static Logger LOGGER = LoggerFactory.getLogger(AgentLoader.class);
+
+    public static void run(String[] args) {
+        String agentFilePath = "/home/adi/Desktop/agent-1.0.0-jar-with-dependencies.jar";
+        String applicationName = "MyAtmApplication";
+
+        //iterate all jvms and get the first one that matches our application name
+        Optional<String> jvmProcessOpt = Optional.ofNullable(VirtualMachine.list()
+          .stream()
+          .filter(jvm -> {
+              LOGGER.info("jvm:{}", jvm.displayName());
+              return jvm.displayName().contains(applicationName);
+          })
+          .findFirst().get().id());
+
+        if(!jvmProcessOpt.isPresent()) {
+            LOGGER.error("Target Application not found");
+            return;
+        }
+        File agentFile = new File(agentFilePath);
+        try {
+            String jvmPid = jvmProcessOpt.get();
+            LOGGER.info("Attaching to target JVM with PID: " + jvmPid);
+            VirtualMachine jvm = VirtualMachine.attach(jvmPid);
+            jvm.loadAgent(agentFile.getAbsolutePath());
+            jvm.detach();
+            LOGGER.info("Attached to target JVM and loaded Java agent successfully");
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/instrumentation/application/Launcher.java

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+package com.baeldung.instrumentation.application;
+
+/**
+ * Created by adi on 6/14/18.
+ */
+public class Launcher {
+    public static void main(String[] args) throws Exception {
+        if(args[0].equals("StartMyAtmApplication")) {
+            new MyAtmApplication().run(args);
+        } else if(args[0].equals("LoadAgent")) {
+            new AgentLoader().run(args);
+        }
+    }
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/instrumentation/application/MyAtm.java

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+package com.baeldung.instrumentation.application;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Created by adi on 6/11/18.
+ */
+public class MyAtm {
+    private static Logger LOGGER = LoggerFactory.getLogger(MyAtm.class);
+
+    private static final int account = 10;
+
+    public static void withdrawMoney(int amount) throws InterruptedException {
+        Thread.sleep(2000l); //processing going on here
+        LOGGER.info("[Application] Successful Withdrawal of [{}] units!", amount);
+
+    }
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/instrumentation/application/MyAtmApplication.java

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+package com.baeldung.instrumentation.application;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MyAtmApplication {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(MyAtmApplication.class);
+
+    public static void run(String[] args) throws Exception {
+        LOGGER.info("[Application] Starting ATM application");
+        MyAtm.withdrawMoney(Integer.parseInt(args[2]));
+
+        Thread.sleep(Long.valueOf(args[1]));
+
+        MyAtm.withdrawMoney(Integer.parseInt(args[3]));
+    }
+
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/logforging/LogForgingDemo.java

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+package com.baeldung.logforging;
+
+import org.owasp.esapi.ESAPI;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class LogForgingDemo {
+
+	private final Logger logger = LoggerFactory.getLogger(LogForgingDemo.class);
+
+	public void addLog(String amount) {
+		logger.info("Amount credited = {}", amount);
+	}
+
+	public static void main(String[] args) {
+		LogForgingDemo demo = new LogForgingDemo();
+		demo.addLog("300");
+		demo.addLog("300 \n\nweb - 2017-04-12 17:47:08,957 [main] INFO Amount reversed successfully");
+		demo.addLog(encode("300 \n\nweb - 2017-04-12 17:47:08,957 [main] INFO Amount reversed successfully"));
+	}
+
+	public static String encode(String message) {
+		message = message.replace('\n', '_').replace('\r', '_').replace('\t', '_');
+		message = ESAPI.encoder().encodeForHTML(message);
+		return message;
+	}
+
+}

core-java-modules/core-java-jvm/src/main/java/com/baeldung/systemgc/DemoApplication.java

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+package com.baeldung.systemgc;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Scanner;
+
+import static java.util.UUID.randomUUID;
+
+public class DemoApplication {
+
+    private static final Map<String, String> cache = new HashMap<String, String>();
+
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+
+        while (scanner.hasNext()) {
+            final String next = scanner.next();
+            if ("fill".equals(next)) {
+                for (int i = 0; i < 1000000; i++) {
+                    cache.put(randomUUID().toString(), randomUUID().toString());
+                }
+            } else if ("invalidate".equals(next)) {
+                cache.clear();
+            } else if ("gc".equals(next)) {
+                System.gc();
+            } else if ("exit".equals(next)) {
+                System.exit(0);
+            } else {
+                System.out.println("unknown");
+            }
+        }
+    }
+}

core-java-modules/core-java-jvm/src/test/java/com/baeldung/classloader/CustomClassLoaderUnitTest.java

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+package com.baeldung.classloader;
+
+import org.junit.Test;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+public class CustomClassLoaderUnitTest {
+
+    @Test
+    public void customLoader() throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
+
+        CustomClassLoader customClassLoader = new CustomClassLoader();
+        Class<?> c = customClassLoader.findClass(PrintClassLoader.class.getName());
+
+        Object ob = c.newInstance();
+
+        Method md = c.getMethod("printClassLoaders");
+        md.invoke(ob);
+
+    }
+
+}

core-java-modules/core-java-jvm/src/test/java/com/baeldung/classloader/PrintClassLoaderUnitTest.java

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+package com.baeldung.classloader;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class PrintClassLoaderUnitTest {
+    @Test(expected = ClassNotFoundException.class)
+    public void givenAppClassLoader_whenParentClassLoader_thenClassNotFoundException() throws Exception {
+        PrintClassLoader sampleClassLoader = (PrintClassLoader) Class.forName(PrintClassLoader.class.getName()).newInstance();
+        sampleClassLoader.printClassLoaders();
+        Class.forName(PrintClassLoader.class.getName(), true, PrintClassLoader.class.getClassLoader().getParent());
+    }
+}

core-java-modules/core-java-jvm/src/test/java/com/baeldung/inlining/ConsecutiveNumbersSumUnitTest.java

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+package com.baeldung.inlining;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class ConsecutiveNumbersSumUnitTest {
+
+    private static final int TOTAL_NUMBERS = 10;
+
+    @Test
+    public void givenTotalIntegersNumber_whenSumCalculated_thenEquals() {
+        ConsecutiveNumbersSum consecutiveNumbersSum = new ConsecutiveNumbersSum(TOTAL_NUMBERS);
+        long expectedSum = calculateExpectedSum(TOTAL_NUMBERS);
+
+        assertEquals(expectedSum, consecutiveNumbersSum.getTotalSum());
+    }
+
+    private long calculateExpectedSum(int totalNumbers) {
+        return totalNumbers * (totalNumbers + 1) / 2;
+    }
+}