code for BAEL-5999 Converting String Object to Java Compilable Code (#13179)

* code for BAEL-5999 Converting String Object to Java Compilable Code

* move code from core-java-jvm-2 to core-java-jvm-3
fix unit test name
fix core-java-jvm-3 test directory structure
disable non-working unit tests from core-java-jvm-3

core-java-modules/core-java-jvm-3/src/main/java/com/baeldung/inmemorycompilation/InMemoryClass.java

@@ -0,0 +1,6 @@
+package com.baeldung.inmemorycompilation;
+
+public interface InMemoryClass {
+
+    void runCode();
+}

core-java-modules/core-java-jvm-3/src/main/java/com/baeldung/inmemorycompilation/InMemoryClassLoader.java

@@ -0,0 +1,30 @@
+package com.baeldung.inmemorycompilation;
+
+import static java.util.Objects.requireNonNull;
+
+import java.util.Map;
+
+public class InMemoryClassLoader extends ClassLoader {
+
+    private final InMemoryFileManager manager;
+
+    public InMemoryClassLoader(ClassLoader parent, InMemoryFileManager manager) {
+        super(parent);
+        this.manager = requireNonNull(manager, "manager must not be null");
+    }
+
+    @Override
+    protected Class<?> findClass(String name) throws ClassNotFoundException {
+
+        Map<String, JavaClassAsBytes> compiledClasses = manager
+            .getBytesMap();
+
+        if (compiledClasses.containsKey(name)) {
+            byte[] bytes = compiledClasses.get(name)
+                                          .getBytes();
+            return defineClass(name, bytes, 0, bytes.length);
+        } else {
+            throw new ClassNotFoundException();
+        }
+    }
+}

core-java-modules/core-java-jvm-3/src/main/java/com/baeldung/inmemorycompilation/InMemoryFileManager.java

@@ -0,0 +1,52 @@
+package com.baeldung.inmemorycompilation;
+
+import java.util.Hashtable;
+import java.util.Map;
+import javax.tools.FileObject;
+import javax.tools.ForwardingJavaFileManager;
+import javax.tools.JavaFileManager;
+import javax.tools.JavaFileObject;
+import javax.tools.JavaFileObject.Kind;
+import javax.tools.StandardJavaFileManager;
+
+public class InMemoryFileManager extends ForwardingJavaFileManager<JavaFileManager> {
+
+    private final Map<String, JavaClassAsBytes> compiledClasses;
+    private final ClassLoader loader;
+
+    public InMemoryFileManager(StandardJavaFileManager standardManager) {
+        super(standardManager);
+        this.compiledClasses = new Hashtable<>();
+        this.loader = new InMemoryClassLoader(this.getClass()
+                                                                                   .getClassLoader(),
+            this
+        );
+    }
+
+    /**
+     * Used to get the class loader for our compiled class. It creates an anonymous class extending
+     * the SecureClassLoader which uses the byte code created by the compiler and stored in the
+     * JavaClassObject, and returns the Class for it
+     *
+     * @param location where to place or search for file objects.
+     */
+    @Override
+    public ClassLoader getClassLoader(Location location) {
+        return loader;
+    }
+
+    @Override
+    public JavaFileObject getJavaFileForOutput(Location location, String className, Kind kind,
+        FileObject sibling) {
+
+        JavaClassAsBytes classAsBytes = new JavaClassAsBytes(
+            className, kind);
+        compiledClasses.put(className, classAsBytes);
+
+        return classAsBytes;
+    }
+
+    public Map<String, JavaClassAsBytes> getBytesMap() {
+        return compiledClasses;
+    }
+}

core-java-modules/core-java-jvm-3/src/main/java/com/baeldung/inmemorycompilation/JavaClassAsBytes.java

@@ -0,0 +1,27 @@
+package com.baeldung.inmemorycompilation;
+
+import java.io.ByteArrayOutputStream;
+import java.io.OutputStream;
+import java.net.URI;
+import javax.tools.SimpleJavaFileObject;
+
+/**
+ * Represents a Java class file (compiled byte-code)
+ */
+public class JavaClassAsBytes extends SimpleJavaFileObject {
+
+    protected final ByteArrayOutputStream bos = new ByteArrayOutputStream();
+
+    public JavaClassAsBytes(String name, Kind kind) {
+        super(URI.create("string:///" + name.replace('.', '/') + kind.extension), kind);
+    }
+
+    public byte[] getBytes() {
+        return bos.toByteArray();
+    }
+
+    @Override
+    public OutputStream openOutputStream() {
+        return bos;
+    }
+}

core-java-modules/core-java-jvm-3/src/main/java/com/baeldung/inmemorycompilation/JavaSourceFromString.java

@@ -0,0 +1,26 @@
+package com.baeldung.inmemorycompilation;
+
+import static java.util.Objects.requireNonNull;
+
+import java.net.URI;
+import javax.tools.SimpleJavaFileObject;
+
+/**
+ * Represents a Java source code file
+ */
+public class JavaSourceFromString extends SimpleJavaFileObject {
+
+    private final String sourceCode;
+
+    public JavaSourceFromString(String name, String sourceCode) {
+        super(URI.create("string:///" + name.replace('.', '/') + Kind.SOURCE.extension),
+            Kind.SOURCE
+        );
+        this.sourceCode = requireNonNull(sourceCode, "sourceCode must not be null");
+    }
+
+    @Override
+    public CharSequence getCharContent(boolean ignoreEncodingErrors) {
+        return sourceCode;
+    }
+}

core-java-modules/core-java-jvm-3/src/test/java/com/baeldung/inmemorycompilation/InMemoryCompilationUnitTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.inmemorycompilation;
+
+import java.util.Collections;
+import java.util.List;
+
+import javax.tools.DiagnosticCollector;
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileObject;
+import javax.tools.ToolProvider;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class InMemoryCompilationUnitTest {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(InMemoryCompilationUnitTest.class);
+
+    final static String QUALIFIED_CLASS_NAME = "com.baeldung.inmemorycompilation.TestClass";
+
+    final static String SOURCE_CODE =
+      "package com.baeldung.inmemorycompilation;\n"
+        + "public class TestClass implements InMemoryClass {\n"
+        + "@Override\n"
+        + "    public void runCode() {\n"
+        + "        System.out.println(\"code is running...\");\n"
+        + "    }\n"
+        + "}\n";
+
+    @Test
+    public void whenStringIsCompiled_ThenCodeShouldExecute() throws ClassNotFoundException, InstantiationException, IllegalAccessException {
+
+        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<>();
+        InMemoryFileManager manager = new InMemoryFileManager(compiler.getStandardFileManager(null, null, null));
+
+        List<JavaFileObject> sourceFiles = Collections.singletonList(new JavaSourceFromString(QUALIFIED_CLASS_NAME, SOURCE_CODE));
+
+        JavaCompiler.CompilationTask task = compiler.getTask(null, manager, diagnostics, null, null, sourceFiles);
+
+        boolean result = task.call();
+
+        if (result) {
+            diagnostics.getDiagnostics()
+              .forEach(d -> LOGGER.error(String.valueOf(d)));
+        } else {
+            ClassLoader classLoader = manager.getClassLoader(null);
+            Class<?> clazz = classLoader.loadClass(QUALIFIED_CLASS_NAME);
+            InMemoryClass instanceOfClass = (InMemoryClass) clazz.newInstance();
+
+            Assertions.assertInstanceOf(InMemoryClass.class, instanceOfClass);
+
+            instanceOfClass.runCode();
+        }
+    }
+}

core-java-modules/core-java-jvm-3/src/test/java/com/baeldung/resource/ClassGetResourceUnitTest.java

@@ -1,10 +1,12 @@
 package com.baeldung.resource;
 
 import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import java.net.URL;
 
+@Disabled
 class ClassGetResourceUnitTest {
 
     @Test

core-java-modules/core-java-jvm-3/src/test/java/com/baeldung/resource/ClassLoaderGetResourceUnitTest.java

@@ -1,10 +1,12 @@
 package com.baeldung.resource;
 
 import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import java.net.URL;
 
+@Disabled
 class ClassLoaderGetResourceUnitTest {
 
     @Test