initial commit

.gitignore

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+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
+/.idea/

README.md

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+### Usage example
+```java
+        var compiler = new RuntimeCompiler();
+        var classname = "com.Test.App";
+        var source = """
+                package com.Test;
+                public class App implements Runnable {
+                    public void run() {
+                        System.out.println("It works! ");
+                    }
+                }
+                """;
+        var compiled = compiler.compile(new SourceCode(classname, source));
+        var constructor = compiled.getConstructor();
+        var instance = (Runnable) constructor.newInstance();
+        instance.run();
+```

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+
+    <groupId>org.example</groupId>
+    <artifactId>TestRuntimeCompiler</artifactId>
+    <version>1.0.0.0</version>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <dependencies>
+        <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>5.11.4</version>
+            <scope>test</scope>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-engine -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <version>5.11.4</version>
+            <scope>test</scope>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.easytesting/fest-assert-core -->
+        <dependency>
+            <groupId>org.easytesting</groupId>
+            <artifactId>fest-assert-core</artifactId>
+            <version>2.0M10</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

src/main/java/ru/kirillius/compiler/CompilationException.java

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+package ru.kirillius.compiler;
+
+import javax.tools.DiagnosticCollector;
+import java.util.StringJoiner;
+
+public class CompilationException extends Exception {
+    public CompilationException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+    private CompilationException(String message) {
+        super(message);
+    }
+
+    public static CompilationException build(DiagnosticCollector<?> diagnostics) {
+        var message = new StringJoiner("\n");
+        diagnostics.getDiagnostics().forEach(diagnostic -> message.add(diagnostic.toString()));
+        return new CompilationException(message.toString());
+    }
+}

src/main/java/ru/kirillius/compiler/CompiledFileBytecode.java

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+package ru.kirillius.compiler;
+
+import javax.tools.SimpleJavaFileObject;
+import java.io.ByteArrayOutputStream;
+import java.io.OutputStream;
+import java.net.URI;
+
+public class CompiledFileBytecode extends SimpleJavaFileObject {
+
+    protected ByteArrayOutputStream bos = new ByteArrayOutputStream();
+
+    public CompiledFileBytecode(String name, Kind kind) {
+        super(URI.create("string:///" + name.replace('.', '/') + kind.extension), kind);
+    }
+
+    public byte[] asByteArray() {
+        return bos.toByteArray();
+    }
+
+    @Override
+    public OutputStream openOutputStream() {
+        return bos;
+    }
+}

src/main/java/ru/kirillius/compiler/RuntimeClassLoader.java

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+package ru.kirillius.compiler;
+
+import static java.util.Objects.requireNonNull;
+
+public class RuntimeClassLoader extends ClassLoader {
+
+    private final RuntimeFileManager manager;
+
+    public RuntimeClassLoader(ClassLoader parent, RuntimeFileManager manager) {
+        super(parent);
+        this.manager = requireNonNull(manager, "manager must not be null");
+    }
+    @Override
+    protected Class<?> findClass(String name) throws ClassNotFoundException {
+        var compiledClasses = manager.getClasses();
+        if (compiledClasses.containsKey(name)) {
+            var bytes = compiledClasses.get(name).asByteArray();
+            return defineClass(name, bytes, 0, bytes.length);
+        } else {
+            throw new ClassNotFoundException();
+        }
+    }
+
+
+}

src/main/java/ru/kirillius/compiler/RuntimeCompiler.java

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+package ru.kirillius.compiler;
+
+
+import javax.tools.DiagnosticCollector;
+import javax.tools.JavaCompiler;
+import javax.tools.ToolProvider;
+import java.util.Collections;
+
+public class RuntimeCompiler {
+
+    private final RuntimeFileManager fileManager;
+    private final JavaCompiler compiler;
+
+    public RuntimeCompiler() {
+        compiler = ToolProvider.getSystemJavaCompiler();
+        if (compiler == null) {
+            throw new RuntimeException("System Java compiler is not available");
+        }
+        fileManager = new RuntimeFileManager(compiler.getStandardFileManager(null, null, null));
+    }
+
+    public Class<?> compile(SourceCode sourceCode) throws CompilationException {
+        var diagnostics = new DiagnosticCollector<>();
+        var task = compiler.getTask(null, fileManager, diagnostics, null, null, Collections.singletonList(sourceCode));
+        if (!task.call()) {
+            throw CompilationException.build(diagnostics);
+        }
+        try {
+            return fileManager.getClassLoader(null).loadClass(sourceCode.getClassName());
+        } catch (ClassNotFoundException e) {
+            throw new CompilationException("Unable to load compiled class", e);
+        }
+    }
+}
+

src/main/java/ru/kirillius/compiler/RuntimeFileManager.java

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+package ru.kirillius.compiler;
+
+import javax.tools.*;
+import java.util.Hashtable;
+import java.util.Map;
+
+public class RuntimeFileManager extends ForwardingJavaFileManager<JavaFileManager> {
+    public RuntimeFileManager(StandardJavaFileManager standardManager) {
+        super(standardManager);
+        classes = new Hashtable<>();
+        loader = new RuntimeClassLoader(this.getClass().getClassLoader(), this);
+    }
+
+    private final ClassLoader loader;
+    private final Map<String, CompiledFileBytecode> classes;
+
+    @Override
+    public ClassLoader getClassLoader(Location location) {
+        return loader;
+    }
+
+    @Override
+    public JavaFileObject getJavaFileForOutput(Location location, String className, JavaFileObject.Kind kind, FileObject sibling) {
+        var bytecode = new CompiledFileBytecode(className, kind);
+        classes.put(className, bytecode);
+        return bytecode;
+    }
+
+    public Map<String, CompiledFileBytecode> getClasses() {
+        return classes;
+    }
+}

src/main/java/ru/kirillius/compiler/SourceCode.java

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+package ru.kirillius.compiler;
+
+import javax.tools.SimpleJavaFileObject;
+import java.net.URI;
+
+import static java.util.Objects.requireNonNull;
+
+public class SourceCode extends SimpleJavaFileObject {
+
+    private final String sourceCode;
+    private final String className;
+
+    public SourceCode(String classname, String sourceCode) {
+        super(URI.create("string:///" + classname.replace('.', '/') + Kind.SOURCE.extension), Kind.SOURCE);
+        this.sourceCode = requireNonNull(sourceCode, "sourceCode must not be null");
+        this.className = classname;
+    }
+
+    @Override
+    public CharSequence getCharContent(boolean ignoreEncodingErrors) {
+        return sourceCode;
+    }
+
+    public String getClassName() {
+        return className;
+    }
+}

src/test/java/ru/kirillius/compiler/RuntimeCompilerTest.java

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+package ru.kirillius.compiler;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.function.Function;
+
+import static org.fest.assertions.api.Assertions.assertThat;
+
+class RuntimeCompilerTest {
+
+    private <T> T compile(SourceCode sourceCode, Class<T> type) {
+        var compiler = new RuntimeCompiler();
+        try {
+            var compiled = compiler.compile(sourceCode);
+            assertThat(compiled).isNotNull();
+            var constructor = compiled.getConstructor();
+            return (T) constructor.newInstance();
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Test
+    public void TestBasicCompilation() {
+        var classname = "com.Test.App";
+        var source = """
+                package com.Test;
+                import java.util.function.Function;
+                public class App implements Function<Integer, Integer> {
+                    @Override
+                     public Integer apply(Integer i) {
+                         return i*2;
+                     }
+                }
+                """;
+
+        var function = (Function<Integer, Integer>) compile(new SourceCode(classname, source), Function.class);
+        assertThat(function.apply(1)).isEqualTo(2);
+    }
+
+    @Test
+    public void TestMultipleCompilation() {
+
+        for (var i = 0; i < 30; i++) {
+            var number = (int) (Math.random() * 1000);
+            var source = createNewSource(number);
+            var function = (Function<Integer, Integer>) compile(source, Function.class);
+            assertThat(function.apply(i)).isEqualTo(number + i);
+        }
+
+
+    }
+
+    @Test
+    public void CompileBrokenCode() {
+        var compiler = new RuntimeCompiler();
+        try {
+            compiler.compile(new SourceCode("broken1", "this code is broken"));
+            throw new RuntimeException();
+        } catch (Exception e) {
+            assertThat(e).isInstanceOf(CompilationException.class);
+        }
+    }
+
+    @Test
+    public void CompileInvalidClassname() {
+        var compiler = new RuntimeCompiler();
+        try {
+            compiler.compile(new SourceCode("broken2", "public class NotBroken{ public int x; }"));
+            throw new RuntimeException();
+        } catch (Exception e) {
+            assertThat(e).isInstanceOf(CompilationException.class);
+        }
+    }
+
+    private SourceCode createNewSource(int magicNumber) {
+        var classname = "com.Test.App" + magicNumber;
+        var source = """
+                package com.Test;
+                import java.util.function.Function;
+                public class App""" + magicNumber + """
+                 implements Function<Integer, Integer> {
+                @Override
+                 public Integer apply(Integer i) {
+                     return i + """ + magicNumber + """
+                    ; }
+                }
+                """;
+
+        return new SourceCode(classname, source);
+    }
+}